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American Water Works Association

Fiberglass Pipe Design

AWWA MANUAL M45

First Edition

FOUNDED

Copyright (C) 1999 American Water Works Association All Rights Reserved

MANUAL OF WATER SUPPLY PRACTICES ---- M45, First Edition

Fiberglass Pipe Design Copyright © 1996 American Water Works Association

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by anymeans, electronic or mechanical, including photocopy, recording, or any information or retrieval system,except in the form of brief excerpts or quotations for review purposes, without the written permission ofthe publisher.

Project Manager and Technical Editor: Sharon PelloweCopy Editor: Martha BallProduction Editor: Alan LivingstonProduction Artist: Karen Staab

Library of Congress Cataloging-in-Publication Data "Fiberglass pipe design manual." xviii, 159p. 17×25 cm.--(Manual of water supply operations: M45) Includes bibliographical (p. ) references and index. ISBN 0-89867-889-7 1. water-pipes. 2. Pipe, glass. I. Series. II. Series: /AWWA manual: M45TD491.A49 no. M45628.1′ 5----dc21 97-4036

CIP

Printed in the United States of America

American Water Works Association6666 West Quincy AvenueDenver, CO 80235

ISBN 0-89867-889-7 Printed on recycled paper


Contents

List of Figures, vii

List of Tables, xi

Preface, xiii

Foreword, xv

Acknowledgments, xvii

Chapter 1 History and Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Introduction, 11.2 History, 11.3 Applications, 21.4 Standards, Specifications, and Reference Documents, 21.5 Terminology, 6

Chapter 2 Materials, Properties, and Characteristics . . . . . . . . . . . . . 7

2.1 General, 72.2 Characteristics, 72.3 The Material System, 82.4 Glass Fiber Reinforcements, 82.5 Resins, 92.6 Other Components, 102.7 Physical Properties, 112.8 Mechanical Properties, 12

Chapter 3 Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1 Introduction, 153.2 Filament Winding, 153.3 Centrifugal Casting, 18References, 20

Chapter 4 Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.1 Hydraulic Characteristics, 214.2 Preliminary Pipe Sizing, 214.3 Typical Pipe Diameters, 224.4 Pressure Loss Calculations, 234.5 Head Loss in Fittings, 274.6 Energy Consumption Calculation Procedure, 294.7 Transient Pressures, 31References, 34

Chapter 5 Buried Pipe Design . . . . . . . . . . . . . . . . . . . . . . . . . . 35

5.1 Introduction, 355.2 Design Terminology, 35

iii


Chapter 5 Buried Pipe Design—continued

5.3 Design Conditions, 365.4 Pipe Properties, 385.5 Installation Parameters, 385.6 Design Procedure, 395.7 Design Calculations and Requirements, 395.8 Axial Loads, 545.9 Special Design Considerations, 545.10 Design Examples, 54References, 71

Chapter 6 Guidelines for Underground Installation of Fiberglass Pipe . . 73

6.1 Introduction, 736.2 Related Documents, 746.3 Terminology, 756.4 In Situ Soils, 776.5 Embedment Materials, 776.6 Trench Excavation, 806.7 Pipe Installation, 826.8 Field Monitoring, 876.9 Contract Document Recommendations, 88References, 88

Chapter 7 Buried Pipe Thrust Restraints . . . . . . . . . . . . . . . . . . . 91

7.1 Unbalanced Thrust Forces, 917.2 Thrust Resistance, 927.3 Thrust Blocks, 937.4 Joints With Small Deflections, 957.5 Restrained (Tied) Joints, 99

Chapter 8 Aboveground Pipe Design and Installation . . . . . . . . . . 103

8.1 Introduction, 1038.2 Test Methods and Physical Properties, 1038.3 Internal Pressure Rating, 1058.4 Thermal Expansion and Contraction, 1078.5 Thermal Expansion Design, 1078.6 Supports, Anchors, and Guides, 1148.7 Bending, 1208.8 Thermal Conductivity, 1208.9 Heat Tracing, 1218.10 Characteristics and Properties, 122References, 124

Chapter 9 Joining Systems, Fittings, and Specials . . . . . . . . . . . . 125

9.1 Introduction, 1259.2 Fiberglass Pipe Joining Systems Classification, 1259.3 Gasket Requirements, 1269.4 Joining Systems Description, 1269.5 Assembly of Bonded, Threaded, and Flanged Joints, 131

iv


9.6 Fittings and Specials, 1349.7 Service Line Connections, 138References, 138

Chapter 10 Shipping, Handling, Storage, and Repair . . . . . . . . . . . 139

10.1 Introduction, 13910.2 Shipping, 13910.3 Handling, 14010.4 Storage, 14210.5 Repair, 143

Glossary, 145

Index, 153

List of AWWA Manuals, 159

v


Figures

3-1 Filament winding process, 16

3-2 Application of impregnated glass reinforcement of a filament wound pipe, 16

3-3 Continuous advancing mandrel method, 17

3-4 Finished pipe emerging from curing oven, 18

3-5 Preformed glass reinforcement sleeve method, 19

3-6 Chopped glass reinforcement method, 19

3-7 Application of glass, resin, and sand, 20

4-1 Friction loss characterisitics of water flow through fiberglass pipe, 23

4-2 Moody diagram for determination of friction factor for turbulent flow, 26

5-1 Definition of common variables used in chapter 5, 37

5-2 Distribution of HS-20 live load through fill for H <2.48 ft, 45

6-1 Trench cross-section terminology, 75

6-2 Examples of bedding support, 82

6-3 Accommodating differential settlement, 84

6-4 Adjacent piping systems, 85

6-5 Proper compaction under haunches, 85

7-1 Thrust force definitions, 92

7-2 Typical thrust blocking of a horizontal bend, 93

7-3 Typical profile of vertical bend thrust blocking, 95

7-4 Restraint of thrust at deflected joints on long-radius horizontal curves, 96

7-5 Computation diagram for earth loads on trench conduits, 97

7-6 Restraint of uplift thrust at deflected joints on long-radius vertical curves, 98

7-7 Thrust restraint with tied joints at bends, 99

7-8 Length of tied pipe on each leg of vertical (uplift) bend, 101

8-1 Fatigue resistance (cyclic internal pressure), 105

8-2 Fatigue resistance (static internal pressure), 106

8-3 Typical expansion joint installation, 111

8-4 Expansion loop dimensions, 112

8-5 Directional change, 114

8-6 Fiberglass wear protection cradle, 116

8-7 Steel wear protection cradle, 116

vii


8-8 Vertical support, 116

8-9 Guide support, 117

8-10 Anchor support, 117

8-11 Typical support, 118

9-1 Tapered bell and spigot joint, 126

9-2 Straight bell and spigot joint, 127

9-3 Tapered bell and straight spigot joint, 127

9-4 Overlay joint construction, 128

9-5 Overlay joint, 128

9-6 Tapered ends overlay joint, 128

9-7 Bell and spigot overlay joint, 128

9-8 Single gasket bell and spigot joint, 129

9-9 Single gasket spigot, 129

9-10 Double gasket bell and spigot joint, 129

9-11 Double gasket spigot, 129

9-12 Gasketed coupling joint, 130

9-13 Gasketed coupling joint, 130

9-14 Restrained gasketed bell and spigot joint, 130

9-15 Restrained gasket coupling joint, 130

9-16 Restrained gasketed threaded bell and spigot O-ring joint, 130

9-17 Fiberglass flange to fiberglass and steel flange joint, 130

9-18 Fiberglass flanges to flanged steel valve connection, 131

9-19 Fiberglass flange with grooved face for O-ring seal, 131

9-20 Mechanical coupling joint, 131

9-21 Compression molding fittings, 134

9-22 Flanged compression molded fittings, 134

9-23 Mitered fitting configurations, 135

9-24 Mitered fitting, 136

9-25 Mitered fitting fabrication, 136

9-26 Mitered fittings, 136

9-27 Mitered fitting field fabrication, 137

9-28 Fittings field assembly, 137

10-1 Pipe shipment by truck, 140

10-2 Single sling handling, 141

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ix

10-3 Double sling handling, 141

10-4 Unitized small-diameter bundle, 141

10-5 Unitized load handling, 141

10-6 Handling nested pipes, 142

10-7 Nesting pipes, 142

10-8 Pipe stacking, 142

10-9 Patch, 143

10-10 Cut out and replace, 143

10-11 Steel coupling, 144


Tables

2-1 Mechanical properties range, 13

4-1 Typical K factors for fiberglass fittings, 28

5-1 Shape factors, 42

5-2 HS-20 and Cooper’s E-80 live loads (psi), 46

5-3 Soil classification chart, 47

5-4 Values for the soil support combining factor Sc, 48

5-5 Values for the modulus of soil reaction E′b for the pipe zone embedment,

psi (MPa), 49

5-6 Values for the modulus of soil reaction E′n for the native soil at pipe zone

elevation, 51

5-7 Conditions and parameters for design examples, 55

6-1 Soil stiffness categories, 78

6-2 Recommendations for installation and use of soils and aggregates for foundation and pipe zone embedment, 79

7-1 Horizontal soil-bearing strengths, 94

8-1 Standard test methods and design properties, 104

8-2 Minimum support width for 120° contact supports, 115

xi


Preface

This is the first edition of AWWA M45, Fiberglass Pipe Design. This manualprovides the user with both technical and general information to aid in the design,specification, procurement, installation, and understanding of fiberglass pipe andfittings. It is a discussion of recommended practice, not an AWWA standard callingfor compliance with certain specifications. It is intended for use by utilities andmunicipalities of all sizes, whether as a reference book or textbook for those notfully familiar with fiberglass pipe and fitting products. Design engineers and con-sultants may use this manual in preparing plans and specifications for new fiber-glass pipe design projects.

The manual covers fiberglass pipe and fitting products and certain appurte-nances, and their application to practical installations, whether of a standard orspecial nature. For adequate knowledge of these products, the entire manual shouldbe studied. Readers will also find the manual a useful source of information whenassistance is needed with specific or unusual conditions. The manual contains a listof applicable national standards, which may be purchased from the respective standardsorganizations (e.g., American Water Works Association, American Society for Testingand Materials, etc.).

xiii


Foreword

AWWA prepares documents, including manuals, for water supply service appli-cations. Chapters 1 and 2 of this manual contain general information about applica-tions other than water supply service for fiberglass pipe for informational andhistorical purposes. The use of this manual is intended for water supply serviceapplications.

xv


Acknowledgments

The American Water Works Association (AWWA) Fiberglass Pipe Design Manualsubcommittee, which developed this manual, had the following personnel at the time:

Richard C. Turkopp, Chair

R.J. Bailey A.M. MayL.L. Cagle T.J. McGrathR.E. Chambers L.E. PearsonM.E. Greenwood B.J. SchrockR.A. Johnson Ron SparksL.A. Kinney Jr. J.J. SwihartM.F. Luckenbill

This manual was also reviewed and approved by the AWWA Standards Committeeand the Standards Council on Thermosetting Fiberglass Reinforced Plastic Pipe. TheStandards Committee on Thermosetting Fiberglass Reinforced Plastic Pipe had the fol-lowing personnel at the time of approval:

Timothy J. McGrath, ChairWilliam F. Guillaume, Vice-Chair

Leo A. Kinney Jr., Secretary

Consumer Members

P.A. Fragassi, Lake County Public Water District, Zion, Ill.W.F. Guillaume, Connecticut Water Company, Clinton, Conn.K.W. Kells,* Connecticut Water Company, Clinton, Conn.L.A. Kinney Jr., US Bureau of Reclamation, Denver, Colo.T.C. Pope Jr., Ted Pope Enterprises, Orlando, Fla.J.J. Swihart,* US Bureau of Reclamation, Denver, Colo.

General Interest Members

S.J. Abrera Jr., Montgomery Watson, Pasadena, Calif.C.H. Angell, C.H. Angell & Associates Inc., Glencoe, Ill.T.E. Arizumi,† Council Liaison, Hawaii Department of Health, Honolulu, HawaiiP.W. Bailey, Alberta Transportation & Utilities, Edmonton, Alta.R.J. Bailey, Centerville, OhioK.M. Bell, Underwriters Laboratories Inc., Northbrook, Ill.J.P. Biro, Houston, Texas

xvii

*Alternate

†Liaison, nonvoting


R.D. Brady, C.C. & E., Bellevue, Wash.R.E. Chambers, Chambers Engineering, P.C., Canton, Mass.J.E. Collins Jr., Gee & Jenson, Jacksonville, Fla.G.S. George, Metcalf & Eddy Inc., Wakefield, Mass.W.W. Graham Jr., W. William Graham Jr. Inc., Little Rock, Ark.J.G. Hendrickson Jr., Olympia Fields, Ill.K.E. Hofer, L.J. Broutman & Associates, Chicago, Ill.J.K. Jeyapalan, American Ventures Inc., Bellevue, Wash.R.A. Johnson, Beetle Engineering Associates Inc., Brandon, Fla.R.J. Kachinsky, Camp, Dresser, & McKee Inc., Cambridge, Mass.T.J. McGrath, Simpson, Gumpertz & Heger Inc., Arlington, Mass.E.W. Misichko,* Underwriters Laboratories, Northbrook, Ill.R.H. Peterson, Municipal Research & Service Center, Kirkland, Wash.E.S. Ralph,† Staff Engineer Liaison, AWWA, Denver, Colo.B.J. Schrock, JSC International Engineering, Carmichael, Calif.

Producer Members

M. Boitz, J-M Manufacturing Company Inc., Livingston, N.J.L.L. Cagle,* Smith Fiberglass Products Inc., Little Rock, Ark.Joe Chen,* J-M Manufacturing Company Inc., Livingston, N.J.B.R. Darrah, The Society of the Plastics Industry of Canada, Don Mills, Ont.M.F. Luckenbill, Ameron, Burkburnett, TexasA.M. May, Smith Fiberglass Products Inc., Little Rock, Ark.L.E. Pearson, Owens Corning Fiberglass Corporation, Brussels, BelgiumRon Sparks, Fibercast, Sand Springs, Okla.R.C. Turkopp, Hobas Pipe USA, Houston, Texas

xviii

*Alternate

†Liaison, nonvoting


History and UseHISTORY AND U SE

1.1 INTRODUCTION ______________________________________Fiberglass pipe is made from glass fiber reinforcements embedded in, or surroundedby, cured thermosetting resin. This composite structure may also contain aggregate,granular, or platelet fillers, thixotropic agents, and pigments or dyes. By selecting theproper combination of resin, glass fibers, fillers, and design, the fabricator can createa product that offers a broad range of properties and performance characteristics.Over the years, the diversity and versatility of materials used to manufacturefiberglass pipe has led to a variety of names for fiberglass pipe. Among these arereinforced thermosetting resin pipe (RTRP), reinforced plastic mortar pipe (RPMP),fiberglass reinforced epoxy (FRE), glass reinforced plastic (GRP), and fiberglassreinforced plastic (FRP). Fiberglass pipes have also been categorized by the particularmanufacturing process—filament winding or centrifugal casting. Frequently, theparticular resin used to manufacture the fiberglass pipe—epoxy, polyester, or vinylester—has been used to classify or grade fiberglass pipes.

Regardless of the many possible combinations, the most common and usefuldesignation is simply “fiberglass pipe.” This name encompasses all of the variousavailable products and allows consideration as a unique and general class ofengineering materials.

1.2 HISTORY ____________________________________________Fiberglass pipe was introduced in 1948. The earliest applications for fiberglasspiping, and still one of the most widely used areas, is in the oil industry. Fiberglasspipe was selected as a cost-effective, corrosion-resistant alternative to protected steel,stainless steel, and other more exotic metals. Product lines expanded to includeincreasingly high-pressure applications and down-hole tubing with threaded connec-tions. In the late 1950s, larger diameters became available and fiberglass pipe wasincreasingly used in the chemical process industry because of the pipe’s inherentcorrosion-resistant characteristics.

AWWA MANUAL M45

Chapter 1

1


From the 1960s through the 1990s fiberglass pipe products have been acceptedin the municipal water and sewage markets. The performance of fiberglass pipe isrecognized as combining the benefits of durability, strength, and corrosion resistance,thus eliminating the need for interior linings, exterior coatings, and/or cathodicprotection. Fiberglass pipe systems offer great design flexibility with a wide range ofstandard pipe diameters and fittings available, as well as an inherent ability forcustom fabrication to meet special needs. Fiberglass pipe is available in diametersranging from 1 in. through 144 in. (25 mm through 3,600 mm). Pressures run fromgravity applications through several thousand psi (kPa). There are few countries inthe world where fiberglass pipe has not been used.

1.3 APPLICATIONS _______________________________________Fiberglass pipe is used in many industries and for a myriad of applications, including:

• chemical process• desalination• down-hole tubing and casing• ducting and vent piping• geothermal• industrial effluents• irrigation• oil fields• potable water• power plant cooling and raw water• sanitary sewers• seawater intake and outfalls• slurry piping• storm sewers• water distribution• water transmission

1.4 STANDARDS, SPECIFICATIONS, AND REFERENCE DOCUMENTS ________________________________________

Many organizations have published nationally recognized standards, test methods,specifications, and recommended practices on fiberglass piping systems and products.These organizations include the American Society for Testing and Materials (ASTM),the American Petroleum Institute (API), the American Society of MechanicalEngineers (ASME), the NSF International (NSF), Underwriters Laboratories (UL),Factory Mutual Research (FM), and the American National Standards Institute(ANSI).

Following is a listing of fiberglass pipe standards and specifications that arecommonly used in specifying, testing, and using fiberglass piping systems.

1.4.1 Product Specifications and ClassificationsASTM D2310 Standard Classification for Machine-Made ‘Fiberglass’

(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe.ASTM D2517 Standard Specification for Reinforced Epoxy Resin Gas Pressure

Pipe and Fittings.

2 FIBERGLASS PIPE DESIGN


ASTM D2996 Standard Specification for Filament-Wound ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe. Applicableto epoxy, polyester, and furan resins in sizes from 1 in. to16 in. (25 mm to 400 mm).

ASTM D2997 Standard Specification for Centrifugally Cast ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe. Applica-ble for 1 in. through 14 in. (25 mm through 350 mm) pipe ofpolyester or epoxy resins.

ASTM D3262 Standard Specification for ‘Fiberglass’ (Glass-Fiber-ReinforcedThermosetting-Resin) Sewer Pipe. Applicable for pipes 8 in.through 144 in. (200 mm through 3,600 mm) diameter, withor without siliceous sand, and polyester or epoxy resin.

ASTM D3517 Standard Specification for ‘Fiberglass’ (Glass-Fiber-ReinforcedThermosetting-Resin) Pressure Pipe. Applicable for pipes 8 in.through 144 in. (200 mm through 3,600 mm) diameter, withor without siliceous sand, and polyester or epoxy resin.

ASTM D3754 Standard Specification for ‘Fiberglass’ (Glass-Fiber-ReinforcedThermosetting-Resin) Sewer and Industrial Pressure Pipe.Applicable for 8 in. through 144 in. (200 mm through3,600 mm) diameter, with or without siliceous sand, andpolyester or epoxy resin.

ASTM D4024 Standard Specification for Machine Made ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Flanges. Appli-cable from 1⁄2 in. through 24 in. (13 mm through 600 mm)ANSI B16.5 150 lb (70 kg) bolt circle flanges.

ASTM D4161 Standard Specification for ‘Fiberglass’ (Glass-Fiber-Rein-forced Thermosetting-Resin) Pipe Joints Using Flexible Elas-tomeric Seals.

ASTM F1173 Standard Specification for Thermosetting Resin FiberglassPipe and Fittings to Be Used for Marine Applications.

API 15LR Specification for Low Pressure Fiberglass Line Pipe. Applicableto 2 in. through 12 in. (50 mm through 300 mm) diameterpipe of epoxy or polyester resin for use at cyclic pressures to1,000 psi (6,895 kPa).

API 15HR Specification for High Pressure Fiberglass Line Pipe. Applicableto 1 in. through 8 in. (25 mm through 200 mm) pipe andfittings for operating pressures over 1,000 psi (6,895 kPa).

API 15AR Specification for Fiberglass Tubing. Applicable to tubingthrough 41⁄2 in. (115 mm) diameters.

AWWA C950 AWWA Standard for Fiberglass Pressure Pipe.

US military specifications.

MIL P24608 Specification for epoxy resin pipe from 1⁄2 in. through 12 in.(13 mm through 300 mm) diameters for 200 psig (1,379 kPa)service at 150°F (66°C) for US Navy shipboard applications.

MIL P28584A Specification for epoxy resin pipe and fittings from 2 in.through 12 in. (50 mm through 300 mm) diameter for use asSteam Condensate Return Lines in continuous service at125 psig (862 kPa) and 250°F (121°C).

MIL P29206A Specification for epoxy or polyester pipe and fittings 2 in.through 12 in. (50 mm through 300 mm) in diameter for POL

HISTORY AND USE 3


services to 150°F (66°C) and 150 psig (1,034 kPa) with surgesto 250 psig (1,724 kPa).

1.4.2 Recommended PracticesDimensions.

ASTM D3567 Standard Practice for Determining Dimensions of ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe and Fittings.

Installation.

ASTM D3839 Standard Practice for Underground Installation of ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe.

API RP15L4 Care and Use of Reinforced Thermosetting Resin Line Pipe(RTRP), Recm. Practice for (Withdrawn).

API RP15A4 Recommended Practice for Care and Use of ReinforcedThermosetting Resin Casing and Tubing (Withdrawn).

API RP1615 Installation of Underground Petroleum Storage Systems.

1.4.3 Standard Test MethodsTensile properties.

ASTM D638 Standard Test Method for Tensile Properties of Plastics.ASTM D1599 Standard Test Method for Short-Time Hydraulic Failure

Pressure of Plastic Pipe, Tubing and Fittings.ASTM D2105 Standard Test Method for Longitudinal Tensile Properties of

‘Fiberglass’ (Glass-Fiber-Reinforced Thermosetting-Resin) Pipeand Tube.

ASTM D2290 Standard Test Method for Apparent Tensile Strength of Ringor Tubular Plastics and Reinforced Plastics by Split DiskMethod.

Compressive properties.

ASTM D695 Standard Test Method for Compressive Properties of RigidPlastics.

Bending properties.

ASTM D790 Standard Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materials.

ASTM D2925 Standard Test Method for Beam Deflection of ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe UnderFull-Bore Flow.

Long-term internal pressure strength.

ASTM D1598 Standard Test Method for Time-to-Failure of Plastic PipeUnder Constant Internal Pressure.

ASTM D2143 Standard Test Method for Cyclic Pressure Strength of Rein-forced Thermosetting Plastic Pipe.

ASTM D2992 Standard Practice for Obtaining Hydrostatic or PressureDesign Basis for ‘Fiberglass’ (Glass-Fiber-Reinforced Thermo-setting-Resin) Pipe and Fittings.



Pipe stiffness.

ASTM D2412 Standard Test Method for Determination of External LoadingCharacteristics of Plastic Pipe by Parallel-Plate Loading.

External pressure.

ASTM D2924 Standard Test Method for External Pressure Resistance of‘Fiberglass’ (Glass-Fiber-Reinforced Thermosetting-Resin)Pipe.

Chemical resistance.

ASTM C581 Standard Practice for Determining Chemical Resistance ofThermosetting Resins Used in Glass-Fiber-Reinforced Struc-tures Intended for Liquid Service.

ASTM D3615 Standard Test Method for Chemical Resistance of ThermosetMolding Compounds Used in the Manufacture of MoldedFittings (Withdrawn–1994).

ASTM D3681 Standard Test Method for Chemical Resistance of ‘Fiberglass’(Glass-Fiber-Reinforced Thermosetting-Resin) Pipe in a De-flected Condition.

1.4.4 Product Listings, Approvals, and Piping CodesNSF International—Standard Nos. 14 and 61. Tests and lists fiberglass

pipe, fittings, and adhesives for use in conveying potable water. Additionally tests andcertifies products as to their classification to an applicable national standard or forspecial properties (Standard 14 only).

Underwriters Laboratories, Inc. Provides established standards for testingand listing fiberglass pipe for use as underground fire water mains and undergroundtransport of petroleum products.

Factory Mutual Research. Has established an approval standard for plasticpipe and fittings for underground fire protection service.

ANSI/ASME B31.1—Power Piping Code.ANSI/ASME B31.3—Chemical Plant and Petroleum Refinery Piping

Code. These codes list some ASTM, AWWA, and API fiberglass pipe specifications asacceptable for use within the code and establishes criteria for their installation anduse. These codes, in addition to other ASME codes, establish rules regarding theapplication of fiberglass piping and provide engineering guidance for the use offiberglass materials.

ANSI/ASME B31.8—Gas Transmission and Distribution Piping SystemsCode. This code lists fiberglass pipe manufactured in compliance with ASTM D2517as acceptable for use within the code.

Department of Transportation, Title 49, Part 192. This is a code of federalregulations that covers the transportation of natural and other gases by pipeline.Minimum federal standards are included.

ASME Boiler and Pressure Vessel Code Case N155. This code provides therules for the construction of fiberglass piping systems for use in Section III,Division I, Class 3 applications in nuclear power plants.

HISTORY AND USE 5


1.5 TERMINOLOGY ______________________________________Fiberglass pipe users may encounter some unique or unfamiliar terminology.

A glossary of terms used in this manual and by the fiberglass pipe industry isprovided at the end of this manual.



Materials, Properties, and Characteristics

MATERIALS, PROPERTIES, AND CHARACTERISTICS

2.1 GENERAL ____________________________________________Fiberglass pipe is a composite material system produced from glass fiber reinforce-ments, thermosetting plastic resins, and additives. By selecting the right combinationand amount of materials and the manufacturing process, the designer can create aproduct to meet the most demanding requirements. The result is a material with abroad range of characteristics and performance advantages.

2.2 CHARACTERISTICS ___________________________________The following is a list of general characteristics of fiberglass composite pipe.

Corrosion resistance. Fiberglass pipe systems are resistant to corrosion, bothinside and out, in a wide range of fluid handling applications. As a result, additionallinings and exterior coatings are not required.

Strength to weight ratio. Fiberglass composite piping systems have excellentstrength to weight properties. When the ratio of strength per unit of weight isconsidered, fiberglass composites surpass iron, carbon, and stainless steels.

Lightweight. Fiberglass composites are lightweight. Fiberglass piping is onlyone-sixth the weight of similar steel products and 10 percent the weight of similarconcrete products.

Electrical properties. Standard fiberglass pipes are nonconductive. Somemanufacturers offer conductive fiberglass piping systems where it is necessary todissipate static electricity buildup when transporting certain fluids, such as jet fuel.

Dimensional stability. Fiberglass composites can maintain the critical toler-ances required of the most demanding structural and piping applications. The

AWWA MANUAL M45

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7


material meets the most stringent material stiffness, dimensional tolerance, weight,and cost criteria.

Low maintenance cost. Fiberglass piping is easy to maintain because it doesnot rust, is easily cleaned, and requires minimal protection from the environment.

2.3 THE MATERIAL SYSTEM ______________________________Fiberglass composites consist of glass fiber reinforcements, thermosetting resins, andadditives, which are designed and processed to meet specific functional performancecriteria. To aid understanding of the performance characteristics of a finishedfiberglass pipe, the interrelationship of the system components is outlined in thischapter.

Fiberglass reinforcement. The amount, type, location, and orientation ofglass fibers in the pipe that will provide the required mechanical strength.

Resin system. Resin selection will provide the physical and chemical properties(e.g., the glass transition temperature, a measurement of resistance to heat, andsoftening or plasticization by solvents and gases).

Fiberglass pipe design optimizes the cost and performance characteristics of thefinished pipe. The design is based on a thorough understanding of the properties andcharacteristics of the materials and processes and the intended application (i.e.,design based on end use).

Following is a brief review of the constituents of fiberglass pipe and how theyinfluence the finished pipe product.

2.4 GLASS FIBER REINFORCEMENTS ______________________The mechanical strength of fiberglass pipe depends on the amount, type, andarrangement of glass fiber reinforcement. Strength increases proportionally with theamount of glass fiber reinforcement. The quantity of the glass fibers (and thedirection the individual strands are placed) determines the strength.

2.4.1 Fiberglass TypesFiberglass materials are available with a variety of different compositions. Thisallows for additional design flexibility to meet performance criteria. All fiberglassreinforcement begins as individual filaments of glass drawn from a furnace of moltenglass. Many filaments are formed simultaneously and are gathered into a “strand.” Asurface treatment (sizing) is added to maintain fiber integrity, establish compatibilitywith resin, and ease further processing by improving consolidation and wet strength.Sizing can also affect resin chemistry and laminate properties.

The most common glass fiber composition used in pipe is “E” type. Other typesof glass may also be used, depending on the pipe application and location within thepipe wall laminate. These glass types include “ECR” and “C” for improved acid andchemical resistance.

2.4.2 Fiberglass Reinforcement FormsThe following is a brief description of the various forms of fiberglass reinforcements.

Continuous roving. These consist of bundled, untwisted strands of glass fiberreinforcement and come as cylindrical packages for further processing. Continuousroving typically is used in filament winding, unidirectional/bidirectional reinforce-ments, and may be processed into chopped strand mat used to provide multidirec-tional reinforcement in pipe and fittings.



Woven roving. This is a heavy, drapable fabric, woven from continuous roving.It is available in various widths, thicknesses, and weights. Woven roving provideshigh strength to large molded parts and is lower in cost than conventional wovenfabrics.

Reinforcing mats. These are chopped strands held together with resinousbinders. There are two kinds of reinforcing mats used in pipe and fittings (i.e.,chopped strand mat and woven roving combination mat). Chopped strand mats areused in medium strength applications for pipe fittings and reinforcing where auniform cross section is desired. Use of the combination mat saves time in handlay-up operations.

Surface veils. These lightweight fiberglass reinforcement mats allow highresin content layers with minimal reinforcement. The surface veil provides extraenvironmental resistance for pipe and fittings, plus a smooth appearance. (Somesurface veils from polyester fibers are also used.)

2.4.3 Reinforcement ArrangementThe three general types of fiber orientation include:

Unidirectional. The greatest strength is in the direction of the fibers. Up to80 percent reinforcement content by weight is possible.

Bidirectional. Some of the fibers are positioned at an angle to the rest of thefibers as with helical filament winding and woven fabrics. This provides differentstrength levels governed by the fiber quantity in each direction of fiber orientation. Acombination of continuous and chopped fibers is also used to provide designeddirectional strength.

Multidirectional (isotropic). This arrangement provides nearly equal, althoughgenerally lower, strength and modulus in all directions. From 10 percent to50 percent reinforcement content, by weight, can be obtained with multidirectionalmaterials such as chopped roving or chopped strand mat.

2.5 RESINS ______________________________________________The second major component of fiberglass pipe is the resin system. Manufacturerschoose a resin system for chemical, mechanical, and thermal properties andprocessability.

The two basic groups of resin systems are thermosetting and thermoplastic.Fiberglass pipe, by definition, uses only the thermosetting resin systems. Thermosetsare polymeric resin systems cured by heat or chemical additives. Once cured, athermoset is essentially infusible (cannot be remelted) and insoluble.

The thermosetting resins used in fiberglass pipe fall into two generalcategories—polyesters and epoxies.

2.5.1 Polyester ResinsPolyester resins are commonly used to produce large-diameter water and sewagepiping. The polyesters have excellent general water and chemical resistance and arenoted for resistance to acids. Although a distinct type of resin, vinyl ester resins arecured and processed like polyesters and can be grouped with the polyesters forgeneral discussion.

The base polyester resin is a solid. It is typically dissolved in styrene monomer,which cross links to provide the final thermoset structure. Polyester resins are curedby organic peroxide catalysts. The type and amount of catalyst will influence gel time,

MATERIALS, PROPERTIES, AND CHARACTERISTICS 9


cure time, curing temperature, and degree of cure. Typical catalysts include methyl ethylketone peroxide (MEKP) and benzoyl peroxide (BPO).

There are several different types of polyester resins that provide a wide range ofperformance characteristics, including:

• orthophthalic polyester• terephthalic polyester• chlorendic acid polyester• novolac epoxy vinyl ester• isophthalic polyester• bisphenol-A fumarate polyester• bisphenol-A vinyl ester

2.5.2 Epoxy ResinsEpoxy resins are commonly used in the manufacture of smaller diameter piping(<30 in. [800 mm] diameter) conveying water, condensates, hydrocarbons, caustics,and dilute acids. Fiberglass epoxy piping is used in the oil fields at pressures up toseveral thousand psi (kPa). Epoxy resins typically allow higher service temperaturesthan polyester.

Epoxy resins cannot be categorized by resin type as easily as polyesters. Thetype of curing agent, or hardener, is critical with epoxy resins because it influencesthe composite properties and performance. The two basic types are amine andanhydride cured bisphenol-A epoxies.

Bisphenol-A epoxy resins are commonly cured with multifunctional primaryamines. For optimum chemical resistance, these mixtures usually require a heat cureand/or post cure. The cured resin has good chemical resistance, particularly inalkaline environments, and can have good temperature resistance. Bisphenol-A epoxyresins may also be cross linked with various anhydrides by using a tertiary amineaccelerator and heat. These cured polymers generally have good chemical resistance,especially to acids.

2.6 OTHER COMPONENTS _______________________________Glass fiber reinforcements and thermosetting resins are the major constituents infiberglass pipe. There are, however, other materials used that influence processingand/or product performance, including fillers, promoters, accelerators, inhibitors, andpigments.

Fillers. Inorganic materials, such as hydrated alumina, glass microspheres,clay, talc, calcium carbonate, sand and calcium silicate, may yield economic,appearance, or performance advantages in fiberglass pipe.

Promoters, accelerators, and inhibitors. Promoters and accelerators ad-vance the action of the catalyst to reduce the processing time. Inhibitors providecontrol over the cure cycle and increase the shelf life of the resin mix.

Pigments. The pigment choice affects the difference in reflected and transmit-ted color, clarity of the resin mix, reaction between dyes and other additives, such ascatalysts, and the end product color fastness and heat resistance.



2.7 PHYSICAL PROPERTIES _______________________________

2.7.1 Chemical ResistanceAll fiberglass pipes provide excellent resistance to water and native ground conditions.They are not subject to general corrosion attack, galvanic corrosion, aerobic corrosion,pitting, dezincification, and graphitic and intergranular corrosion, which may harmmetallic pipes. Fiberglass pipes are subject to some environmental stress and agingeffects, the determination of which is part of the fiberglass pipe design procedure.

Resistance to corrosion in aggressive environments is one of the primary reasonsfor specifying fiberglass pipe. Fiberglass pipe resists a wide range of chemicals. Thechemical resistance of fiberglass pipe depends primarily on the particular resinmatrix material used. Although other factors, such as liner construction, cure, andfabrication method may influence the chemical resistance of fiberglass pipe, theprimary factor is the resin. The resins can be selected to provide chemical resistanceto a broad range of materials. The fiberglass pipe manufacturer should be consultedfor performance information for a particular chemical application.

2.7.2 Temperature ResistanceThe temperature resistance of fiberglass pipe also depends largely upon the resinmatrix. The allowable upper limit of service temperature will also be influenced bythe chemical environment and the stress condition of the piping system. In general,the effect of chemical agents is more aggressive at higher concentrations and elevatedtemperatures. However, for the typical use temperatures encountered in water supplysystems (33°F to 90°F [1°C to 32°C]), fiberglass pipe is unaffected by servicetemperature, and there is no need to rerate or derate fiberglass pipe pressureperformance. Fiberglass pipe is virtually unaffected by colder temperatures.Therefore, normal shipping, handling, and storage procedures, as discussed inchapter 10, may be used in sub-zero weather. Users and installers of fiberglass pipeshould be aware, however, that the coefficient of thermal expansion for fiberglass pipeis generally higher than for most metal pipes. This must be recognized and provisionsmade in design and installation to accommodate expansion and contraction, particularlyin aboveground applications.

2.7.3 Abrasion ResistanceFiberglass pipe provides generally good abrasion resistance and can be custom madefor extremely abrasive service by lining the pipe with sand, silica flour, carborundum,or ceramic beads or tiles, or by incorporating resilient liner materials such aspolyurethanes. Special lining materials should match or exceed the hardness andabrasiveness of the contents being transported through the pipe or provide a highlevel of toughness and resilience.

2.7.4 Flame RetardantsThe thermosetting resin systems used to fabricate fiberglass pipes are organicmaterials. Therefore, under the proper combination of heat and oxygen, athermosetting resin, like any organic matter, will burn. If required, the fireperformance of fiberglass pipe can be enhanced by using resin systems that containhalogens or phosphorous. Use of hydrated fillers also enhances flame resistance.Other additives, primarily antimony oxides, can also increase the effectiveness ofhalogenated resins.



Fire performance testing requires small samples and specialized test methodsand may not indicate how a material will perform in a full-scale field or fire situation.The fiberglass pipe manufacturer should be consulted for specific information on thecombustion performance of fiberglass pipe.

2.7.5 Weathering ResistanceMost of the thermosetting resin systems used in the fabrication of fiberglass pipe aresubject to some degradation from ultraviolet (UV) light. This degradation, however, isalmost entirely a surface phenomenon. Weathering studies have shown that thestructural integrity of fiberglass pipe is not affected by exposure to UV. The use ofpigments, dyes, fillers, or UV stabilizers in the resin system, or painting of exposedsurfaces, can help reduce significantly any UV surface degradation. Surfaces exposedto UV will generally be fabricated with a resin rich layer. Other weathering effects,such as rain or saltwater, are resisted fully by the inherent corrosion resistance offiberglass pipe.

2.7.6 Resistance to Biological AttackFiberglass pipe will not deteriorate or break down under attack from bacteria or othermicroorganisms, nor will it serve as nutrient to microorganisms, macroorganisms, orfungi. No cases are known where fiberglass pipe products have suffered degradationor deterioration due to biological action. No special engineering or installationprocedures are required to protect fiberglass pipe from biological attack. Someelastomers may be susceptible to biological attack. Any biological attack precautionsthat might be required for elastomeric gaskets should be followed with fiberglass pipeas with any other piping material.

2.7.7 TuberculationSoluble encrustants, such as calcium carbonate, in some water supplies do not tend toprecipitate onto the smooth walls of fiberglass pipe. Because fiberglass pipe isinherently corrosion resistant, there is no tuberculation of the fiberglass pipe causedby corrosion by-products.

2.8 MECHANICAL PROPERTIES ___________________________The design flexibility inherent with glass fiber reinforced plastic materials and therange of manufacturing processes used precludes the simple listing of fiberglass pipemechanical properties. For this reason, fiberglass piping product standards areperformance based and detail the required product performance requirement ratherthan thickness-property tables. Table 2-1 gives a range of mechanical propertiesavailable with fiberglass pipe. The pipe manufacturer must be consulted for themechanical properties of a particular product.



Table 2-1 Mechanical properties range

Tensile Strength (psi) 7,000 – 80,000 (50 – 550 MPa)Tensile Modulus (psi) 0.5 × 106 – 5 × 106 (3.5 × 103 – 34.5 × 103 MPa)Flexural Strength (psi) 10,000 – 70,000 (70 – 480 MPa)Flexural Modulus (psi) 1 × 106 – 5 × 106 (6.9 × 103 – 34.5 × 103 MPa)Coefficient of Thermal Expansion(in./in./°F) 8 × 10–6 – 30 × 10–6 (14 × 10–6 – 54 × 10–6 mm/mm/°C)Specific Gravity 1.2 – 2.3Compressive Strength (psi) 10,000 – 40,000 (70 – 280 MPa)



ManufacturingMANUFACTURIN G

3.1 INTRODUCTION ______________________________________Machine-made fiberglass pipe is produced using two basic processes: filamentwinding and centrifugal casting. Each of the processes produces a pipe withcharacteristics that while unique, and which may be advantageous for someapplications, will meet the performance requirements of AWWA Standard C950.

3.2 FILAMENT WINDING _________________________________Filament winding is the process of impregnating glass fiber reinforcement with resin,then applying the wetted fibers onto a mandrel in a prescribed pattern. Fillers, ifused, are added during the winding process. Chopped glass rovings may be used assupplemental reinforcement. Repeated application of wetted fibers, with or withoutfiller, results in a multilayered structural wall construction of the required thickness.After curing, the pipe may undergo one or more auxiliary operations such as jointpreparation. The inside diameter (ID) of the finished pipe is fixed by the mandreloutside diameter (OD). The OD of the finished pipe is variable and is determined bythe pipe wall thickness.

The concepts of the filament winding process are illustrated in Figure 3-1.Within the broad definition of filament winding there are several methods usedincluding reciprocal, continuous, multiple mandrel, and ring and oscillating mandrel,each of which is described briefly. Figure 3-2 shows the application of impregnatedglass reinforcement onto a mandrel during production of a filament wound pipe.

3.2.1 Reciprocal MethodThis is the most widely used filament winding production method. In this method thefiber placement head with the associated resin bath drives back and forth past arotating mandrel (see Figure 3-1). The angle of fiber placement relative to themandrel axis is controlled by the synchronized translational speed of the bath and therotational speed of the mandrel.

AWWA MANUAL M45

Chapter 3

15


Rotation

Translates

Resin Bath

90° Wrap Angle

0° Axis

0° Wrap Angle

Mandrel

90° Axis

Fiber PlacementHead

Fibers (Continuous)

Reprinted with permission from Fiberglass Pipe Handbook, Fiberglass Pipe Institute, New York, N.Y.

Figure 3-1 Filament winding process

Figure 3-2 Application of impregnated glass reinforcement of a filament wound pipe



3.2.2 Continuous MethodsIn one type of continuous process, pipe is made on one or more mandrels, which movepast stations that apply fiberglass tapes preimpregnated with resin or glass fiber andresin. The winding angles are controlled through a combination of longitudinalmandrel speed, mandrel rotation (if used), or the rotation of planetary glassapplication stations. Once started, these methods produce pipe continuously, stoppingonly to replenish or change material components.

A second type of continuous process is the continuous advancing mandrel, whichis composed of a continuous steel band supported by beams, which forms acylindrically shaped mandrel. The beams rotate, friction pulls the band around, androller bearings allow the band to move longitudinally so that the entire mandrelcontinuously moves in a spiral path toward the end of the machine. Raw materials(continuous fibers, chopped fibers, resin, and aggregate fillers) are fed to the mandrelfrom overhead. Release films and surfacing materials are applied from rolls adjacentto the mandrel. After curing, a synchronized saw unit cuts the pipe to proper length.This method is illustrated in Figure 3-3. Finished pipe emerging from the curing ovenis shown in Figure 3-4.

3.2.3 Multiple Mandrel MethodIn this method, a single materials application system applies wetted glassreinforcement simultaneously to two or more mandrels. When the winding operationfinishes, the mandrels are indexed to a new position for curing while another set ofmandrels is wound.

Saw

Roving Rack

Finished Pipe

Curing Oven With Exhaust Fan

Surface Mat

Metering Pumps

Mixing Tanks

Drive Unit

Release Film

Panel

Top View Winding Equipment

Source: Owens Corning Engineered Pipe Systems, Brussels, Belgium.

Figure 3-3 Continuous advancing mandrel method

MANUFACTURING 17


3.2.4 Ring and Oscillating Mandrel MethodThe use of 360˚ glass delivery systems, sometimes in combination with an oscillatingmandrel, allows production with both high- and low-winding angles as single circuitpatterns (without interlayer crossovers).

3.3 CENTRIFUGAL CASTING Centrifugal casting is a process used to manufacture tubular goods by applying resinand reinforcement to the inside of a mold that is rotated and heated, subsequentlypolymerizing (curing) the resin system. The OD of the finished pipe is determined bythe ID of the mold tube. The ID of the finished pipe is variable and is determined bythe amount of material introduced into the mold. Other materials, such as sand orfillers, may be introduced in the process during manufacture of the pipe.

Two different methods of centrifugal casting are used and are described briefly.Preformed glass reinforcement sleeve method. A preformed glass rein-

forcement sleeve is placed inside a steel mold. As the steel mold rotates, resin and afiller, if used, are placed within the mold by means of a feed tube that moves in andout of the mold, thus wetting out the preformed sleeve. This method is illustrated inFigure 3-5.

Chopped glass reinforcement method. Varying proportions of chopped glassreinforcement, resin, and aggregate are introduced simultaneously, by layer, from afeeder arm that moves in and out of the mold. This method is illustrated inFigure 3-6. Application of glass, resin, and sand within a rotating mold is shown inFigure 3-7.


Figure 3-4 Finished pipe emerging from curing oven



Air Blower to Remove Heat Generatedby Exothermic Reaction of the Resin and Catalyst

Inject Catalyzed Resin in RotatingMold Tube

Insert Fiberglass, Remove Mandrel

Figure 3-5 Preformed glass reinforcement sleeve method

Source: Hobas Pipe USA Inc., Houston, Texas.

Figure 3-6 Chopped glass reinforcement method

MANUFACTURING 19


REFERENCES


Figure 3-7 Application of glass, resin, and sand

Standard for Fiberglass Pressure Pipe. 1995.ANSI/AWWA C950. Denver, Colo.: Ameri-can Water Works Association.



HydraulicsHYDRAULICS

4.1 HYDRAULIC CHARACTERISTICS _______________________The hydraulic characteristics of fiberglass pipe include:

• The smooth interior results in low fluid resistance, which could lowerhorsepower requirements for pumped systems. This characteristic couldcontribute to a substantial cost savings over the life of a typical pipingsystem.

• The interior pipe surface typically remains smooth over time in most fluidservices. Therefore, fluid resistance does not increase with age.

• The smooth interior allows the pipe diameter to be reduced while maintainingthe desired flow.

• Inside diameter (ID) is typically larger than IDs of many other pipematerials of the same nominal size and provide a larger pathway for fluidflow.

This chapter provides a basis for analysis of the flow capacity, economics, andfluid transient characteristics of fiberglass pipe.

4.2 PRELIMINARY PIPE SIZING ___________________________The first step in designing a piping system is to determine the pipe size needed totransport a specific amount of fluid. Many engineers have adopted rules that areindependent of pipe length but rely on typical or limiting fluid velocities or allowablepressure drop per 100 ft (30 m) of pipe. After the fluid velocity or the pressure drop isknown, it is easy to size a pump to provide the proper flow rate at the requiredpressure. The following equations are guidelines for the initial sizing of pipe.

AWWA MANUAL M45

Chapter 4

21


4.2.1 Maximum Velocity for Water

v = 48/ρ 0.33 (4-1)

Where:

v = fluid velocity, ft/s

ρ = fluid density, lb/ft3

= 62.4 lb/ft3 for water

4.2.2 Maximum Velocity for Corrosive or Erosive Fluids

v = 24/ρ 0.33 (4-2)

4.2.3 Minimum Pipe Diameter for Water

d = 0.73[(Q)/(SG)]0.5/ρ 0.33 (4-3)

Where:

d = internal pipe diameter, in.

Q = flow rate, gpm

SG = fluid specific gravity, dimensionless (1 for water)

4.2.4 Minimum Pipe Diameter for Corrosive or Erosive Fluids

d = 1.03 [(Q)/(SG)]0.5/ρ0.33 (4-4)

4.3 TYPICAL PIPE DIAMETERS ____________________________The equations in Sec. 4.2 represent the minimum pipe diameters or maximum fluidvelocities for water and corrosive (or erosive) liquid flow. Typical diameters for fiberglasspressure pipe and suction pipe can be calculated using the following equations.

4.3.1 Typical Diameters for Pressure Pipe Service

d = 0.321 [Q/(SG)2]0.434 (4-5)

4.3.2 Typical Diameters for Suction Pipe Service

d = 0.434 [(Q)/(SG)2]0.434 (4-6)

4.3.3 Conversion of Flow Rate to Fluid Velocity

v = 0.409 (Q/d2) (4-7)



4.4 PRESSURE LOSS CALCULATIONSHead loss, or pressure drop, occurs in all piping systems because of elevation changes,turbulence caused by abrupt changes of direction, and friction within the pipe and fittings.

A number of different computational methods can be used to determine the headloss in fiberglass pipe. The most common methods are the Hazen-Williams, Manning,and the Darcy-Weisbach equations. The suitability of each method depends on thetype of flow (gravity or pumped) and the level of accuracy required. The relativelysmooth interior surface of fiberglass pipe should be considered when selecting theroughness coefficient or friction factor in these methods.

4.4.1 Hazen-Williams EquationThe Hazen-Williams equation is applicable to water pipes under conditions of fullturbulent flow. Although not as technically correct for all velocities as other methods,the Hazen-Williams equation has gained wide acceptance in the water andwastewater industries because of its simplicity.


Figure 4-1 Friction loss characteristics of water flow through fiberglass pipe

1

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Velocity(ft/s)

Pipe

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.

HYDRAULICS 23


The Hazen-Williams equation is frequently presented in nomograph form asshown in Figure 4-1. Note, however, that graphical solutions usually are valid forwater only. When fluids other than water are encountered, a more universal solutionsuch as the Darcy-Weisbach equation should be used. The Hazen-Williams equation isvalid for turbulent flow and will usually provide a conservative solution fordetermining the head loss in fiberglass pipe.

hf = 0.2083 (100/C)1.85 (Q1.85/d4.87) (4-8)

Where:

hf = friction, ft H2O / 100 ft

C = Hazen−Williams roughness coefficient = 150 (typical value for fiberglass pipe)

d = inside diameter (ID), in.

NOTE: Graphs and examples use nominal pipe size for simplicity. The actual IDshould be used in hydraulic calculations.

4.4.2 Simplified Hazen-WilliamsMany engineers prefer a simplified version of the Hazen-Williams equation:

hf = [42.7 Q/(C) d2.63)]1.852 (4-9)

4.4.3 Head Loss Converted to Pressure DropHead loss for any liquid is converted into pressure drop using the following equation:

p = (Hf) (SG)/ 2.31 (4-10)

Where:

p = pressure drop, psi

Hf = hf L/100

SG = fluid specific gravity, dimensionless

L = line length, ft

New fiberglass pipe has a Hazen-Williams roughness coefficient C value of150–165. A design value of 150 is frequently used with fiberglass pipe.

These values compare favorably to many other pipe materials that have a lowerinitial value than fiberglass and degrade over time due to internal corrosion and scalebuild-up. The amount of internal corrosion or scale formation is a function of waterquality and varies with location and water source.

Example 4-1: Use of the Hazen-Williams equation. Compute the frictionalpressure loss in a 1,500-ft long, 10-in. diameter fiberglass pipe transporting 2,000 gpm ofwater.

Step 1. Compute the head loss using Eq 4-9:

hf = [(42.7) (2,000) / (150) (102.63)]1.852

hf = 1.70 ft H2O / 100 ft



Then:

Total head loss Hf = (1.70) (1,500/100) = 25.5 ft

Step 2. Convert head loss to pressure drop using Eq 4-10:

p = (25.5) (1.0) / 2.31 = 11 psi

4.4.4 Manning EquationThe Manning equation typically solves gravity flow problems where the pipe is onlypartially full and is under the influence of an elevation head only.

Qm = (1.486/n) (S)0.5 (A) (R)0.667 (4-11)

Where:

Qm = flow rate, ft3/s

S = hydraulic slope ft/ft = (H1 − H2) /L

H1 = upstream elevation, ft

H2 = downstream elevation, ft

L = length of pipe section, ft

n = Manning roughness coefficient

= 0.009 for typical fiberglass pipe

R = hydraulic radius (A/Wp), ft

A = cross-sectional area of pipe, ft2

Wp = wetted perimeter of pipe, ft

4.4.5 Darcy-Weisbach EquationThe Darcy-Weisbach equation states that pressure drop is proportional to the squareof the velocity and the length of the pipe. It is inversely proportional to the diameterof the pipe. The primary advantage of this equation is that it is valid for all fluids inboth laminar and turbulent flow. The disadvantage is that the Darcy-Weisbachfriction factor is a variable. Once preliminary sizing of the pipe diameter has beencompleted, the next step is to determine whether the flow pattern within the pipe islaminar or turbulent. This characterization of the flow is necessary in the selection ofthe appropriate friction factor to be used with the Darcy-Weisbach equation. The well-known Reynolds number equation is used to characterize the fluid flow:

Re = (ID) (v)/µ (4-12)

Where:

Re = Reynolds number, dimensionless

µ = fluid kinematic viscosity, ft3/s

ID = inside diameter, ft

HYDRAULICS 25


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Reprinted with permission from L. F. Moody, Friction Factors for Pipe Flow, ASME, 345 E. 47th St.,New York, NY 10017.

Figure 4-2 Moody diagram for determination of friction factor for turbulent flow



This guideline determines the type of flow from the Reynolds number:

Flow Type Reynolds Number

Laminar flow Re ≤ 2,000Transition flow zone 2,000 < Re < 4,000Turbulent flow Re ≥ 4,000

Simply stated, the Darcy-Weisbach equation is as follows:

Hf = f L (v2)/2 (ID) g (4-13)

If flow in the pipe is laminar (i.e., Re ≤ 2,000), the friction factor f1 reduces to

f1 = 64/Re (4-14)

NOTE: Friction factor for laminar flow is denoted as f1 and ft denotes friction factor forturbulent flow.

When the flow regime is turbulent (i.e., Re ≥ 4,000), the friction factor can bedetermined from the Moody diagram found in most fluid mechanics texts (seeFigure 4-2). Fiberglass pipe has a surface roughness parameter e equal to 1.7 ×10–5 ft. When divided by the pipe diameter (e/ID), the friction factor ft for turbulentflow can be extracted from the smooth pipe segment of the diagram. The frictionfactor for turbulent flow can also be calculated from the Colebrook equation:

1/ft0.5 = −2 log [(e/ID) /3.7] + 2.51/(Re) (ft

0.5 ) (4-15)

Where:

ft = Moody friction factor

e = surface roughness parameter

= 1.7 × 10−5 for fiberglass pipe

This equation is difficult to solve because it is implicit in ft and requires a trial anderror iterative solution. The following simplified equation relates the friction factor to theReynolds number and is accurate to within 1 percent of the Colebrook equation:

ft = [1.8 log (Re/7)]−2 (4-16)

4.5 HEAD LOSS IN FITTINGS _____________________________Head loss in fittings is frequently expressed as the equivalent length of pipe that isadded to the straight run of pipe. This approach has sufficient accuracy for manyapplications and is used most often with the Hazen-Williams or Manning equations.The approach does not consider turbulence and subsequent losses created by differentfluid velocities. When tabular data are not available, or when additional accuracy isnecessary, head loss in fittings (or valves) can be determined using loss coefficients (Kfactors) for each type of fitting. Table 4-1 provides the typical K factors. In thisapproach the K factor for each fitting is multiplied by the velocity head of the fluidflow. Eq 4-17 illustrates the loss coefficient approach.

HYDRAULICS 27


Hf = K (v2/2g) (4-17)

Where:

K = K factor for each fitting type from Table 4-1.

Many hydraulic handbooks provide K factors for various types of fittings andvalves not included in this manual.

The total head loss in a system includes, but is not limited to, losses fromfittings, the head loss from the straight run pipe, and head losses due to changes inelevation.

Example 4-2: Determine the pipe diameter, working pressure, andpressure class on a pipeline. The pipeline requires 5,000 ft of pipe, four each 90°elbows (double miter), and three each 45° elbows (single miter) with an elevationchange of 25 ft. Assume kinematic viscosity µ = 0.00001. The flow rate is 8,000 gpm.

Step 1. Determine minimum diameter (Eq 4-3):

d = 0.73 [Q/(SG)]0.5 / ρ0.33 = 0.73 [8,000 /(1)]0.5 /62.40.33

= 16.7 in.

Use next larger commercial size, which is 18 in. nominal diameter for thisexample, (ID = 18.19 in. = 1.516 ft)

Step 2. Compute average fluid velocity (Eq 4-7):

v = 0.409 (Q/d2) = 0.409 (8,000/(18.19)2) = 9.89 ft/s

Step 3. Compute Reynolds number (Eq 4-12):

Re = (ID) (v) / µ = (1.516) (9.89) / 0.00001 = 1,499,324

Since Re is greater than 4,000, the flow is in the turbulent range.

Step 4. Compute the friction factor (Eq 4-16):

ft = [1.8 log (Re/7)]−2 = [1.8 log (1,499,324/7)]−2 = 0.0109

Table 4-1 Typical K factors for fiberglass fittings

Type of Fitting K Factor

90° elbow, standard 0.590° elbow single miter 1.490° elbow double miter 0.890° elbow triple miter 0.6

180° return bend 1.3Tee, straight flow 0.4

Tee, flow to branch 1.4Tee, flow from branch 1.7

Reducer, single size reduction 0.7Reducer, double size reduction 3.3



Step 5. Compute system friction losses by combining Eq 4-13 and Eq 4-17:

Hf = [Sum K + ft (L/ID)] (v2/2g)

Quantity Fitting type K factor Total K factors4 90° elbows 0.8 3.23 45° elbows 0.5 1.5

Total = 4.7

Hf = [4.7 + 0.0109 (5,000/1.516)] (9.892/2 (32.2)) = 61.5 ft

Step 6. Combine friction and elevation head:

Htotal = Hf + He = 61.5 + 25 = 86.5 ft

Step 7. Convert head loss to working pressure drop Pw (Eq 4-10):

WpPw = Htotal (SG)/ 2.31 = 86.5 (1) / 2.31 = 37.5 psi

The solution to example 4-2 is a total working pressure of 37.5 psi. Althoughthe working pressure by itself would require a 50 psi pressure class, a higher classmay be selected to account for potential water hammer in the line or to meetminimum AWWA Standard C950 pipe stiffness requirements. In this example thenext higher pressure class is 100 psi. Refer to example 4-4 to verify that thispressure class is satisfactory for water hammer.

4.6 ENERGY CONSUMPTION CALCULATION PROCEDURE ___Fluid flow resistance and operating economics are sometimes considered to be mutuallyexclusive characteristics by many designers. However, pipeline operating costs are driven,in large part, by the frictional resistance of the pipe and the corresponding powerconsumption. The frictional effects of metallic pipeline materials are further complicated bythe possibility of internal corrosion as a function of water quality (pH, Langeliercalcium-carbonate index, etc.) and time. In other words, the internal friction of a pipelinecan increase over time due to the effects of water corrosion on the pipe material.

The pipeline design process should consider the operating economics of thepipeline material. This section outlines the basic procedure for determining the headloss and relative economic merits when considering different pipe materials.

4.6.1 Pipeline Economic Analysis ProcedureStep 1. Calculate the head loss (Eq 4-9):

Hf = [42.7 Q/(C) (d2.63)]1.852

Step 2. Convert head loss to pump horsepower demand:

hp = QρHf/ 33,000 (4-18)

HYDRAULICS 29


Where:

hp = horsepower required

ρ = fluid density (8.34 lb/gal for water)

Step 3. Calculate the annual energy usage:

Ec = (hp) (24 h/d) (365 d/year) (0.7457 kw-h/hp-h)/eff (4-19)

Where:

Ec = annual energy consumption, kw -h/year

eff = pump efficiency, usually 75 to 85 percent

Step 4. Calculate average annual energy cost (AEC):

AEC = (Ec) (UEC) (4-20)

Where:

AEC = annual energy cost, $

UEC = unit energy cost, $/kw-h

Example 4-3: Comparative power cost calculation. A 10,000 ft-long, 6-in.diameter pipeline is to deliver 500 gpm of water on a year-round basis. The designeris considering using fiberglass pipe with an average Hazen-Williams coefficient C = 150and another material that will have an average Hazen-Williams coefficient C = 100 overthe life of the pipeline. Compute the average annual energy cost AEC for eachcandidate material and the total energy cost over the 20-year service life of the projectwith a unit cost of power of $0.06/kw-h.

Step 1. Calculate the head loss for each material (Eq 4-9):

For fiberglass pipe:

hf = [(42.7) (500) / (150) (6.00)2.63]1.852

= 1.58 ft/100 ft

= 158 ft for the system

For alternate material:

= [(42.7) (500) / (100) (6.00)2.63]1.852

= 3.34 ft/100 ft

= 334 ft for the system

Step 2. Convert head loss to horsepower demand (Eq 4-18):

Fiberglass Pipe Alternate Material

hp = (500)(8.34)(158)/33,000 = (500)(8.34)(334)/33,000 = 19.97 hp = 42.21 hp



Step 3. Calculate the annual energy consumption Ec using an 80 percentpump efficiency and Eq 4-19:

Ec = (19.97) (24) (365) (0.7457)/0.80 = (42.21) (24) (365) (0.7457)/0.80xxx= 163,063 kw-h = 344,662 kw-h

Step 4. Calculate the AEC (Eq 4-20) and determine the total energy cost over20 years:

AEC = (163,063) (0.06) = (344,662) (0.06) = $9,784/year = $20,680/year = $195,676 over 20 years = $413,594 over 20 years

More sophisticated techniques (net present value, life cycle costing, etc.) thatconsider the time value of money can also be used to evaluate the relative economicsof alternative pipe materials. These techniques consider the installed cost of pipe inthe calculation and future cash flow are discounted by an appropriate discount rate.

4.7 TRANSIENT PRESSURES _______________________________Internal shock, or pressure surge, known commonly as water hammer results fromabrupt change of fluid velocity within the system. Under certain conditions, theseshock forces can reach magnitudes sufficient to rupture or collapse a piping system,regardless of the material of construction. The transient pressure is the rapidlymoving wave that increases and decreases the pressure in the system depending onthe source of the transient and direction of wave travel.

Rapid valve closure can result in the buildup of shock waves due to theconversion of kinetic energy of the moving fluid to potential energy that must beaccommodated. These pressure waves will travel throughout the piping system andcan cause damage far away from the wave source.

4.7.1 Water HammerThe magnitude of water hammer is a function of the fluid properties and velocity, themodulus of elasticity and wall thickness of the pipe material, the length of the line,and the speed in which the momentum of the fluid changes. The relatively highcompliance (low modulus of elasticity) of fiberglass pipe contributes to a self-dampingeffect as the pressure wave travels through the piping system. The magnitude of thepressure wave in a metallic piping system is much higher due to the higher modulusof elasticity of these materials.

In addition to rapid valve closure or opening, sudden air release and pumpstart-up or shut-down can create water hammer. Water hammer pressure surges donot show up readily on conventional Bourdon tube gauges because of the slowresponse of the instrument. The net result of water hammer can be excessivepressures, pipe vibration, or movement that can cause failure in pipe and fittings.

In some cases, anchoring the piping system may mitigate pipe vibration andmovement problems. In other cases, mechanical valve operators, accumulators,rupture discs, surge relief valves, feedback loops around pumps, etc., may be requiredto protect against or remove the source of water hammer.

Good design practice usually prevents water hammer in most systems.Installation of valves that cannot open or close rapidly is one simple precaution. In

HYDRAULICS 31


addition, pumps should never be started in empty discharge lines unless slow-opening,mechanically actuated valves can increase the flow rate gradually.

4.7.2 Water Hammer CalculationThe Talbot equation calculates surge pressure due to a change in velocity:

Ps = (a/g) (SG/2.3) (∆v) (4-21)

in which:

a = 12/[ (ρ/g)(1/k + d/E (t) ) ]0.5 (4-22)

Where:

Ps = pressure surge deviation normal, psig

a = wave velocity, ft/s

∆v = change in flow velocity, ft/s

ρ = fluid density, lb/ft3

SG = fluid specific gravity, dimensionless

k = bulk modulus of compressibility of liquid, psi (300,000 psi for water)

E = modulus of elasticity of pipe wall, psi

d = pipe ID, in.

t = pipe wall thickness, in.

g = gravitational constant, 32.2 ft/s2

The pressure class Pc must be greater than or equal to the sum of the workingpressure Pw and surge pressure Ps divided by 1.4 (see chapter 5, Sec. 5.7.1.3).

Many fluid mechanics and hydraulic handbooks provide procedures such as theprevious Talbot equation for calculating pressure surges as a result of a single valveclosure in simple piping systems. Sophisticated fluid transient computer programsare also available to analyze water hammer in complex multibranch piping systemsunder a variety of conditions.

Example 4-4: Surge pressure calculation. Determine if the maximum surgepressure for the pipe in example 4-2 is within the 40 percent allowance criteria. Assumea full instantaneous change in velocity equal to the flow velocity of the pipe. The filamentwound fiberglass pipe has a tensile modulus of 3,000,000 psi and pressure class of100 psi (wall thickness t = 0.21 in.). The bulk modulus of water is 300,000 psi.

Step 1. Calculate the wave velocity (Eq 4-22):

a = 12/[ ( ρ/g) (1/k + ID/E (t)) ]0.5

= 12/ [ (62.4/32.2) (1/300,000 + 18.19/3,000,000 (0.21) ) ]0.5

= 1,515 ft/s

Step 2. Compute the surge pressure (Eq 4-21):

Ps = (a/g) (SG/2.3) (∆v)

= (1,515 / 32.2) (1 / 2.3) (9.89)

= 202 psi



Step 3. Check compliance with the maximum system pressure requirement:

Pc ≥ (Pw + Ps) / 1.40

From example 4-2, Pw = 37.5 psi and Pc = 100 psi

(37.5 + 202)/1.40 = 171 psi

This value exceeds the 100 psi pressure class.In this particular design example, the designer has two options. The first is to increase

the pipe pressure class two pressure classes from 100 psi to 200 psi and maintain the samepipe diameter. This choice would allow a total system pressure of 280 psi.

The second alternative is to increase both the pipe size and pressure class to thenext larger diameter and pressure classification. The larger pipe diameter will reduceoperating pressure (less friction) and lower fluid velocity. In this case, the next largerdiameter is 20 in. (ID = 20.19 in. = 1.683 ft). The wall thickness of 20 in. diameter,150 psi pressure class pipe is 0.23 in.

For purposes of illustration, the second option will be demonstrated in thisexample. Refer to example 4-2 for additional information.

Step 4. Calculate the new velocity using the larger diameter (Eq 4-7):

v = 0.409 (Q/d2) = 0.409 (8,000)/(20.19)2 = 8.03 ft/s

Note that this velocity is lower than the 9.89 ft/s in example 4-2.

Step 5. Recalculate the working pressure using the new diameter:A) Reynolds number (Eq 4-12):

Re = (ID) (v)/µ = (1.683) (8.03)/0.00001 = 1,351,450

B) Compute friction factor (Eq 4-16):

ft = [1.8 log (Re/7 ) ]−2 = [1.8 log (1,351,450/7 ) ]−2 = 0.011

C) Compute system friction losses by combining Eq 4-13 and Eq 4-17:

Hf = [Sum K + ft (L/ID) ] (v2/2 g)

From example 4-2, the total K value is 4.7.

Hf = [4.7 + 0.011 (5,000/1.683) ] ( (8.03)2/2 (32.2) ) = 37.5 ft

D) Compute total head:

Htotal = Hf + He = 37.5 + 25 = 62.5 ft

E) Convert head to working pressure (Eq 4-10):

Pw = H total (SG)/2.31 = 62.5 (1)/2.31 = 27 psi

Step 6. Recalculate the pressure surge using the new fluid velocity: A) Compute wave velocity (Eq 4-21):

a = 12/[(ρ/g) (1/k + ID/E (t) ]0.5

= 12/ [ (62.4/32.2) (1/300,000 + 20.19 / 3,000,000 (0.23) ]0.5

= 1,509 ft/s

HYDRAULICS 33


B) Recalculate the pressure surge using larger diameter (Eq 4-20):

Ps = (a/g) (SG/2.3) (∆v)

= (1,509/32.2) (1/2.3) (8.03)

= 164 psi

Step 7. Recheck compliance with the maximum system pressure requirement:

Pc ≥ (Pw + Ps) /1.40

Pw = 27 psi

(27 + 164)/1.40 = 136 psi

Pc = 150 ≥ 136 psi

The maximum system pressure requirement is satisfied by using a largerdiameter pipe with a higher pressure class. The designer would typically evaluate theeconomics of using a larger diameter pipe with the new pressure class or using thesame diameter with a higher pressure class.

REFERENCES _____________________________________________

Benedict, R.P. 1980. Fundamentals of PipeFlow. New York: John Wiley & Sons.

Brater, E.F., and H.W. King. 1982. Hand-book of Hydraulics. 6th ed. New York:McGraw-Hill.

Fiberglass Pipe Institute. 1989. FiberglassPipe Handbook. New York: FiberglassPipe Institute.

Kent, G.R. 1978. Preliminary Pipeline Sizing.Chemical Engineering.

Sharp, W.W., and T.M. Walski. 1988. Predict-ing Internal Roughness in WaterMains, Jour. AWWA 80(11):34.




Buried Pipe DesignBURIED PIPE DESIGN

5.1 INTRODUCTION ______________________________________The structural design procedure for buried fiberglass pipe involves establishment ofdesign conditions, selection of pipe classes and corresponding pipe properties, selection ofinstallation parameters, and performance of pertinent calculations to ensure that thedesign requirements of Sec. 5.7 are satisfied. If the results of any calculation indicatethat a requirement is not satisfied, it will be necessary to upgrade installationparameters or select a pipe with different properties, or both, and redo pertinentcalculations. Special information and calculations not covered in this chapter may berequired in unusual cases (see Sec. 5.9).

Both rigorous and empirical methods are used in the design of fiberglass pipe. Inaddition to short-term tests, many performance limits are determined at 50 yearsthrough statistical extrapolation of data obtained from long-term tests under simulatedservice conditions. Design stress or strain values are obtained by reducing performancelimits using appropriate design factors. Design factors are established to ensure adequateperformance over the intended service life of the pipe by providing for variations inmaterial properties and loads not anticipated by design calculations. Design factors arebased on judgment, past experience, and sound engineering principles.

The design method discussed in this chapter applies in concept to pipe withuniform walls and to pipe with ribbed-wall cross sections. However, for design of pipewith ribbed walls, some of the equations must be modified to allow for the specialproperties of this pipe. Also, additional calculations not addressed in this chapter maybe required to ensure an adequate design for a ribbed-wall cross section.

5.2 DESIGN TERMINOLOGY ______________________________The following definitions apply to buried pipe design as discussed in this chapter.

Working pressure Pw. The maximum anticipated, long-term operating pres-sure of the fluid system resulting from typical system operation.

Pressure class Pc. The maximum sustained pressure for which the pipe isdesigned in the absence of other loading conditions.

AWWA MANUAL M45

Chapter 5

35


Surge pressure Ps. The transient pressure increase above the workingpressure, sometimes called water hammer, that is anticipated in a system as a resultof a change in the velocity of the fluid, such as when valves are operated or whenpumps are started or stopped.

Surge allowance Psa. That portion of the surge pressure that can beaccommodated without changing pressure class. The surge allowance is expected toaccommodate pressure surges usually encountered in typical systems.

Hydrostatic design basis HDB. The long-term hydrostatic hoop strength of aspecific fiberglass pipe material as determined by tests and detailed evaluationprocedures in accordance with ANSI/AWWA Standard C950, Pressure Classessubsection on long-term hydrostatic design pressure.

Design factor FS. A specific number greater than one used to reduce a specificmechanical or physical property in order to establish a design value for use incalculations.

Variables. For definitions of variables used in equations and formulas in thischapter, see Figure 5-1.

5.3 DESIGN CONDITIONS ________________________________Design conditions are largely determined by required flow rate and flow velocitylimitations, hydraulics, pipeline elevations and associated geology and topography,available right-of-ways, and installation requirements.

B′ = empirical coefficient of elastic support (dimensionless)Bd = trench width at pipe springline, in. (mm)D = mean pipe diameter, in. (mm)Df = shape factor per Table 5-1 (dimensionless)DL = deflection lag factor (dimensionless)E = ring flexural modulus of elasticity, psi (MPa)E′ = composite modulus of soil reaction, psi (MPa)E′b = modulus of soil reaction of the pipe zone backfill embedment, psi

(MPa)E′n = modulus of soil reaction of the native soil at pipe elevation, psi (MPa)EH = hoop tensile modulus of elasticity, psi (MPa)EI = stiffness factor per unit length of pipe wall, in.2-lb/in. (m2-N/m)F = load per unit length, lb/in. (N/m)FS = design factorF/∆y = pipe stiffness, psi (MPa)H = burial depth to top of pipe, ft (m)h = height of ground surface above top of pipe, in. (mm)hw = height of water surface above top of pipe, in. (mm)HDB = hydrostatic design basis, psi (kPa) (for stress basis) or in. per in.

(mm/mm) (for strain basis)ID = inside diameter, in. (mm)I = moment of inertia of pipe wall for ring bending, in. (mm) to the fourth

power per lineal in. (mm)K = [2nL/πD]2

Kx = bedding coefficient (dimensionless)L = distance between rigid ring stiffeners, in. (mm)L1 = dimension of area of wheel load at pipe crown depth in the direction

of travel, ft. (m) (see Figure 5-2)



L2 = dimension of area of wheel load at pipe crown depth transverse to the direction of travel, ft. (m) (see Figure 5-2)

If = impact factor (dimensionless)n = number of lobes formed at buckling ≥ 2OD = outside diameter, in. (mm)P = vehicular traffic load (wheel load), lb (kg)PS = pipe stiffnessPc = pressure class, psi (kPa)Ps = surge pressure, psi (kPa)Psa = surge allowance, psi (kPa)Pv = internal vacuum pressure, psi (kPa)Pw = working pressure, psi (kPa)qa = allowable buckling pressure, psi (kPa)qu = unconfined compressive strength, US tons/ft2 (N/m2)r = mean pipe radius, in. (mm)rc = rerounding, coefficient (dimensionless)Rw = water buoyancy factor (dimensionless)Sb = long-term, ring-bending strain, in./in. (mm/mm)Sc = soil support combining factor (dimensionless)Si = ultimate hoop tensile strength, psi (kPa)Sr = hoop tensile stress, psi (kPa) or strain, in./in. (mm/mm) at pressure

classt = thickness of pipe reinforced wall, per ASTM D3567, in. (mm)tL = thickness of liner (when used), in. (mm)tt = total thickness of pipe wall and liner (when used), in. (mm)Wc = vertical soil load on the pipe, lb/in.2 (N/m)WL = live load on the pipe, lb/in.2 (N/m)γs = specific weight of the soil, lb/ft3 (N/m3)γw = specific weight of water, lb/in.3 (N/m3)υhl = Poisson’s ratio, applied hoop stressυlh = Poisson’s ratio, applied longitudinal stress∆y = predicted vertical pipe deflection, in. (mm)∆ya = maximum allowable long-term vertical pipe deflection, in. (mm)σb = maximum ring-bending stress due to deflection, psi (kPa)σc = maximum stress due to combined loading, psi (kPa)σpr = working stress due to internal pressure, psi (kPa)δd = maximum permitted long-term installed deflection, in. (mm)εb = maximum ring-bending strain due to deflection, in./in. (mm/mm)εc = maximum strain due to combined loading, in./in. (mm/mm)εpr = working strain due to internal pressure, in./in. (mm/mm)

Figure 5-1 Definition of common variables used in chapter 5

5.3.1 Head LossesHydraulic head loss due to pipe friction may be significantly lower for fiberglass pipethan for other types of pipe due to fiberglass pipe’s generally smoother bores andfreedom from tuberculation and corrosion. This is reflected in typical long-term flowcoefficient values of 0.009 for Manning’s n and 150 for the Hazen-Williams’ C. Thedesigner may wish to consider this in establishing design conditions. (See chapter 4on hydraulics.)

BURIED PIPE DESIGN 37


5.3.2 Surge PressuresSurge pressures should be calculated on the basis of the pipe hoop modulus andthickness-to-diameter ratio for given system design parameters (discussed later inthis chapter). Excessive surge pressures should be identified in the design phase, andthe causative condition should be eliminated or automatic surge-pressure reliefprovided or a higher pressure class selected.

5.3.3 Basic Design ConditionsDesign conditions that should be established before performing structural designcalculations are as follows:

• Nominal pipe size (Tables 1 through 6, ANSI/AWWA Standard C950)• Working pressure Pw (Sec. 5.7.1.2)• Surge pressure Ps (Sec. 5.7.1.3)• Soil conditions for the pipe zone embedment and native material at pipe

depth (Sec. 5.7.3.8)• Soil specific weight γs (Sec. 5.7.3.5)• Depth of cover, minimum and maximum (Sec. 5.7.3.5)• Vehicular traffic load P (Sec. 5.7.3.6)• Internal vacuum pressure Pv (Sec. 5.7.5)• Average and maximum service temperature (Sec. 5.9)

5.4 PIPE PROPERTIES _____________________________________Preliminary pipe pressure class selection can usually be made on the basis of workingpressure, surge pressure, and external loads established in Sec. 5.7. Properties at theanticipated average and maximum service temperature for a given class of a specificpipe product should be obtained from the manufacturer or the manufacturer’sliterature. Values for ring stiffness, axial strength, and hoop tensile strength given inANSI/AWWA Standard C950 are minimum requirements. Some pipe products mayhave significantly higher values for these properties. The design may require materialproperties and structural capacities greater than those given as minimums inANSI/AWWA Standard C950. Pipe properties necessary to perform design calcula-tions include the following:

• Nominal reinforced wall thickness t and liner thickness tL (ANSI/AWWAStandard C950)

• Hoop tensile modulus of elasticity EH (Sec. 5.7.1.1)• Hydrostatic design basis HDB• Ring flexural modulus of elasticity E (Sec. 5.7.2)• Minimum pipe stiffness F/∆y (ANSI/AWWA Standard C950)• Long-term ring-bending strain Sb (Sec. 5.7.2.2)• Poisson’s ratios υhl, υlh (Sec. 5.7.5)

5.5 INSTALLATION PARAMETERS _________________________The primary installation parameters that must be selected according to the siteconditions and planned installation are the type of backfill soil immediately aroundthe pipe (pipe zone backfill), degree of compaction, and the native soil characteristicsat the pipe elevation. Initial selection of these parameters may be controlled byprevailing standard specifications, the project soils boring report, manufacturers’



recommendations, or past experience. A given combination of soil type and degree ofcompaction will largely determine the following values required for design calculations:

• bedding coefficient Kx (Sec. 5.7.3.4)• modulus of soil reaction E′ (Tables 5-3, 5-4, and 5-6 and Sec. 5.7.3.8)• deflection lag factor DL (Sec. 5.7.3.3)

5.6 DESIGN PROCEDURE _________________________________With conditions, properties, and installation parameters established in accordancewith Sec. 5.3 through Sec. 5.5, satisfaction of the requirements listed in Sec. 5.7 canbe checked by design calculations. The calculations may be made using either stressor strain, depending on the basis used to establish a particular product performancelimit. The procedure for using design calculations to determine whether pipe meetsthe requirements discussed in Sec. 5.7 is as follows:

1. Calculate Pc from HDB and pipe dimensions (Sec. 5.7.1.1) 2. Check working pressure Pw (Sec. 5.7.1.2) 3. Check surge pressure Ps (Sec. 5.7.1.3) 4. Calculate allowable deflection from ring bending (Sec. 5.7.2) 5. Determine soil loads Wc and live loads WL (Sec. 5.7.3.5 and Sec. 5.7.3.6, respectively) 6. Calculate the composite modulus of soil reaction E′ (Sec. 5.7.3.8) 7. Check deflection prediction ∆y/D (Sec. 5.7.3) 8. Check combined loading (Sec. 5.7.4) 9. Check buckling (Sec. 5.7.5)

See Sec. 5.10 for step-by-step example design calculations.

5.7 DESIGN CALCULATIONS AND REQUIREMENTS _________

5.7.1 Internal Pressure5.7.1.1 Pressure class Pc. The pressure class in ANSI/AWWA Standard C950, isrelated to the long-term strength, or HDB, of the pipe as follows:

For stress basis HDB:

Pc ≤

HDBFS

2tD

(5-1)

For strain basis HDB:

Pc ≤

HDBFS

2EHt

D

(5-2)

Where:

Pc = pressure class, psiHDB = hydrostatic design basis, psi, for stress basis, or in./in. for strain basis

FS = minimum design factor, 1.8t = thickness of pipe reinforced wall per ASTM D3567, in.

D = mean pipe diameter, in., as follows:For inside diameter ID series pipe (Tables 1 and 2, ANSI/AWWA

Standard C950): D = ID + 2tL + t



For outside diameter OD series (Tables 3, 4, 5, and 6, ANSI/AWWA Standard C950):

D = OD − tWhere:

tL = thickness of liner (when used), in. ID = inside diameter, in. OD = outside diameter, in.

EH = hoop tensile modulus of elasticity for pipe, psi

Hydrostatic design basis (HDB). The HDB of fiberglass pipe varies for differentproducts, depending on the materials and composition used in the reinforced wall andin the liner. The HDB may be defined in terms of reinforced wall hoop stress or hoopstrain on the inside surface.

Temperature and service life. The HDB at ambient temperature must be estab-lished by testing in accordance with ANSI/AWWA Standard C950 for each fiberglass pipeproduct by each manufacturer. The required practice is to define projected productperformance limits at 50 years. Performance limits at elevated temperature depend onthe materials and type of pipe wall construction used. The manufacturer should beconsulted for HDB values appropriate for elevated temperature service.

Design factors. Two separate design factors are required in ANSI/AWWA StandardC950 for internal pressure design.

The first design factor is the ratio of short-term ultimate hoop tensile strengthSi to hoop tensile stress Sr at pressure class Pc. This factor ensures that the stress orstrain due to the short-term peak pressure conditions do not exceed the short-termhydrostatic strength of the pipe. The hoop tensile strength values given in Table 10 ofANSI/AWWA Standard C950 reflect a minimum design factor of 4.0 on initialhydrostatic strength.

The second design factor is the ratio of HDB to hoop stress or strain Sr atpressure class Pc. This factor ensures that stress or strain due to sustained workingpressure does not exceed the long-term hoop strength of the pipe as defined by HDB.For fiberglass pipe design, this minimum design factor is 1.8.

Both design factors should be checked. Either design factor may govern pipedesign, depending on long-term strength regression characteristics of the particularpipe product. Prudent engineering may dictate an increase or decrease in eitherdesign factor, depending on the certainty of the known service conditions.

5.7.1.2 Working pressure Pw. The pressure class of the pipe should be equalto or greater than the working pressure in the system, as follows:

Pc ≥ Pw (5-3)

Where:

Pw = working pressure, psi

5.7.1.3 Surge pressure Ps. The pressure class of the pipe should be equal toor greater than the maximum pressure in the system, due to working pressure plussurge pressure, divided by 1.4, as follows:

Pc ≥ (Pw + Ps)

1.4(5-4)

Where:

Ps = surge pressure, psi



The treatment of surge pressures reflects the characteristics of the pipe andmaterials covered by ANSI/AWWA Standard C950. Field or factory hydrotesting atpressures up to 2 Pc is acceptable and is not governed by Eq 5-3 and Eq 5-4.

Calculated surge pressure Ps. The surge-pressure calculations should be performedusing recognized and accepted theories. (See chapter 4 on hydraulics.)

Calculated surge-pressure magnitudes are highly dependent on the hoop tensileelastic modulus and thickness-to-diameter (t/D) ratio of the pipe. Because of this, thedesigner should generally expect lower calculated surge pressures for fiberglass pipethan for pipe materials with a higher modulus or thicker wall or both. For example,an instantaneous change in flow velocity of 2 ft/s (0.6 m/s) would result in acalculated surge-pressure increase of approximately 40 psi (276 kPa) for fiberglasspipe with a modulus of 3,000,000 psi (20,680 MPa) and a t/D ratio of 0.01.

Surge allowance Psa. The surge allowance is intended to provide for rapidtransient pressure increases typically encountered in transmission systems. Thesurge-pressure allowance of 0.4 Pc is based on the increased strength of fiberglasspipe for rapid strain rates. Special consideration should be given to the design ofsystems subject to rapid and frequent cyclic service. The manufacturer should beconsulted for specific recommendations.

5.7.2 Ring BendingThe maximum allowable long-term vertical pipe deflection should not result in aring-bending strain (or stress) that exceeds the long-term, ring-bending straincapability of the pipe reduced by an appropriate design factor. Satisfaction of thisrequirement is assured by using one of the following formulas:

For stress basis:

σb = Df E (∆ya

D) (

tt

D) ≤

SbEFS (5-5)

For strain basis:

εb = Df (∆ya

D) ( tt

D) ≤

Sb

FS(5-6)

Where:

σb = maximum ring-bending stress due to deflection, psiDf = shape factor per Table 5-1, dimensionlessE = ring flexural modulus of elasticity for the pipe, psi

∆ya = maximum allowable long-term vertical pipe deflection, in. Sb = long-term, ring-bending strain for the pipe (ANSI/AWWA C950), in.D = mean pipe diameter, in.

FS = design factor, 1.5εb = maximum ring-bending strain due to deflection, in./in.tt = t + tL, in.

5.7.2.1 Shape factor Df. The shape factor relates pipe deflection to bendingstress or strain and is a function of pipe stiffness, pipe zone embedment material andcompaction, haunching, native soil conditions, and level of deflection. Table 5-1 givesvalues for Df, assuming inconsistent haunching, deflections of at least 2 to 3 percent,and stable native soils or adjustments to trench width to offset poor conditions.



Values given in Table 5-1 are for typical pipe zone embedment materials. For otherpipe zone embedment materials, use the highest Df value for each pipe stiffness.

5.7.2.2 Long-term, ring-bending strain Sb. The long-term, ring-bendingstrain varies for different products, depending on materials and type of constructionused in the pipe wall. Long-term, ring-bending strain should be determined as definedin ANSI/AWWA Standard C950.

5.7.2.3 Bending design factor. Prudent design of pipe to withstand bendingrequires consideration of two separate design factors.

The first design consideration is comparison of initial deflection at failure to themaximum allowed installed deflection. The ring stiffness test (level B) in ANSI/AWWAStandard C950 subjects a pipe ring to deflections far exceeding those permitted inuse. This test requirement demonstrates a design factor of at least 2.5 on initialbending strain.

The second design factor is the ratio of long-term bending stress or strain to thebending stress or strain at the maximum allowable long-term deflection. Forfiberglass pipe design, this minimum design factor is 1.5.

5.7.3 DeflectionBuried pipe should be installed in a manner that will ensure that external loads willnot cause a long-term decrease in the vertical diameter of the pipe exceeding themaximum allowable deflection (∆ya/D) established in Sec. 5.7.2 or the permitteddeflection, (δd/D), as required by the engineer or manufacturer, whichever is less.This requirement may be stated as follows:

∆y/D ≤ δd/D ≤ ∆ya/D (5-7)

Where:

∆yD

=(DLWc + WL) Kx

0.149PS + 0.061 E′× 100%

(5-8)

Table 5-1 Shape factors

PipeStiffness

Pipe-Zone Embedment Material and Compaction

Gravel* Sand†

Dumped to Slight‡ Moderate to High§ Dumped to Slight‡ Moderate to High

psi kPa Shape Factor Df (dimensionless)

9 62 5.5 7.0 6.0 8.018 124 4.5 5.5 5.0 6.536 248 3.8 4.5 4.0 5.572 496 3.3 3.8 3.5 4.5

* GW, GP, GW–GC, GW–GM, GP–GC, and GP–GM per ASTM D2487 (includes crushed rock).† SW, SP, SM, SC, GM, and GC or mixtures per ASTM D2487.‡ < 85% Proctor density (ASTM D698), <40% relative density (ASTM D4253 and D4254).§ ≥ 85% Proctor density (ASTM D698), ≥40% relative density (ASTM D4253 and D4254).


§


∆y/D = predicted vertical pipe deflection as a percent of mean pipe diameter

DL = deflection lag factor to compensate for the time-consolidation rate of the soil, dimensionless (Sec. 5.7.3.3)

Wc = vertical soil load on the pipe, psi (Sec. 5.7.3.5)

WL = live load on the pipe, psi (Sec. 5.7.3.6)

Kx = bedding coefficient, dimensionless (Sec. 5.7.3.4)

PS = pipe stiffness, lb/in./in., psi (Sec. 5.7.3.7)

E′ = composite modulus of soil reaction, psi (Sec. 5.7.3.8)

5.7.3.1 Deflection calculations. Design calculations that require deflection asan input parameter should show the predicted deflection ∆y/D as well as the maximumallowable deflection ∆ya/D, at which the allowable design stress or strain is not exceeded.The maximum permitted deflection δd/D should be used in all design calculations.

5.7.3.2 Deflection prediction. When installed in the ground, all flexible pipewill undergo deflection, defined here to mean a decrease in vertical diameter. Theamount of deflection is a function of the soil load, live load, native soil characteristicsat pipe elevation, pipe embedment material and density, trench width, haunching,and pipe stiffness. Many theories have been proposed to predict deflection levels;however, in actual field conditions, pipe deflections may vary from calculated valuesbecause the actual installation achieved may vary from the installation planned.These variations include the inherent variability of native ground conditions andvariations in methods, materials, and equipment used to install a buried pipe.

Field personnel responsible for pipe installation must follow procedures designedto ensure that the long-term pipe deflection is less than ∆ya as determined inSec. 5.7.2, or as required by the engineer or manufacturer, whichever is less. Aspresented previously and as augmented by information provided in the followingsections, Eq 5-8 serves as a guideline for estimating the expected level of short-termand long-term deflection that can be anticipated in the field. Eq 5-8 is a form of theIowa formula, first published by Spangler* in 1941. This equation is the best knownand documented of a multitude of deflection-prediction equations that have beenproposed. As presented in this chapter, the Iowa formula treats the major aspects ofpipe-soil interaction with sufficient accuracy to produce reasonable estimates of loadinduced field deflection levels.

Pipe deflection due to self-weight and initial ovalization due to pipe backfillembedment placement and compaction are not addressed by this method. Thesedeflections are typically small for pipe stiffnesses above 9 psi to 18 psi (62 kPa to124 kPa) (depending on installation conditions). For pipe stiffnesses below thesevalues, consideration of these items may be required to achieve an accurate deflectionprediction.

Application of this method is based on the assumption that the design valuesused for bedding, backfill, and compaction levels will be achieved with good practiceand with appropriate equipment in the field. Experience has shown that deflectionlevels of any flexible conduit can be higher or lower than predicted by calculation ifthe design assumptions are not achieved.


* Spangler, M.G., and R.L. Handy. Soil Engineering. Harper & Row, New York,N.Y. (4th ed., 1982).


5.7.3.3 Deflection lag factor DL. The deflection lag factor converts theimmediate deflection of the pipe to the deflection of the pipe after many years. Theprimary cause of increasing pipe deflection with time is the increase in overburdenload as soil “arching” is gradually lost. The vast majority of this phenomenon occursduring the first few months of burial and continues for up to a couple of years,depending on the frequency of wetting and drying cycles. Secondary causes ofincreasing pipe deflection over time are the time-related consolidation of the pipe zoneembedment and the creep of the native soil at the sides of the pipe. These causes aregenerally of much less significance than increasing load and may not contribute to thedeflection for pipes buried in relatively stiff native soils with dense granular pipe zonesurrounds. For long-term deflection prediction, a DL value of >1.00 is appropriate.

5.7.3.4 Bedding coefficient Kx. The bedding coefficient reflects the degree ofsupport provided by the soil at the bottom of the pipe and over which the bottomreaction is distributed. Assuming an inconsistent haunch achievement (typical directbury condition), a Kx value of 0.1 should be used. For uniform shaped bottom support,a Kx value of 0.083 is appropriate.

5.7.3.5 Vertical soil load on the pipe Wc. The vertical soil load on thepipe may be considered as the weight of the rectangular prism of soil directlyabove the pipe. The soil prism would have a height equal to the depth of earthcover and a width equal to the pipe outside diameter.

Wc = γs H144

(5-9)

Where:

Wc = vertical soil load, psi

γs = unit weight of overburden, lb/ft3

H = burial depth of top of pipe, ft

5.7.3.6 Live loads on the pipe WL. The following calculation assumes afour-lane road with an AASHTO HS-20 truck centered in each 12-ft (3.7-m) wide lane.The pipe may be perpendicular or parallel to the direction of truck travel or anyintermediate position. Other design truck loads can be specified as required by projectneeds and local practice.

1. Compute L1, load width (ft) parallel to direction of travel, see Figure 5-1.

L1 = 0.83 + 1.75 H (5-10)

2. Compute L2, load width (ft) perpendicular to direction of travel, see Figure 5-2.

2 ft < H < 2.48 ft L2 = 1.67 + 1.75 H (5-11)

H ≥ 2.48 ft L2 = (43.67 + 1.75H)/8 (5-12)

3. Compute WL:

WL = P (If)/{144 (L1) (L2) } (5-13)



Where:

WL = live load on pipe, psi

P = 16,000 lb (HS-20 wheel load)

If = impact factor

= 1.1 for 2 ft < H < 3 ft

= 1.0 for H ≥ 3 ft

P

10 in.0.83 ft

20 in.1.67 ft

1.67 ft

Direction of Travel

0.83 ft

H

L2 = 1.67 + 1.75 (H)L1 = 0.83 + 1.75 (H)

0.83 ft

NOTE: For H ≥ 2.48 ft, see part 2 of the L2 formula. (Change accounts for overlapping influence areas from adjacentwheel loads.)

Figure 5-1 Distribution of HS-20 live load through fill for H <2.48 ft



This computation is independent of pipe diameter and results in live loadstabulated in Table 5-2. Table 5-2 also includes live loads for Cooper E-80 railroad loads.

5.7.3.7 Pipe stiffness PS. The pipe stiffness is the product of the ring flexuralmodulus of elasticity E of the pipe-wall material, and the moment of inertia I of a unit lengthof pipe divided by the quantity 0.149 times the mean radius cubed (see Eq 5-14). The momentof inertia is equal to tt

3/12, where tt is the total wall thickness. When other than uniform wallconstruction is used, consult the manufacturer for the proper moment of inertia.

PS = EI

0.149 (r + ∆y/2)3 (5-14)

The pipe stiffness can be determined by conducting parallel-plate loading testsin accordance with ASTM D2412. During the parallel-plate loading test, deflectiondue to loads on the top and bottom of the pipe is measured, and pipe stiffness iscalculated from the following equation:

PS = F∆y

(5-15)

Where:

F = load per unit length, lb/in.

∆y = vertical pipe deflection, in.

5.7.3.8 Modulus of soil reaction E′. The vertical loads on a flexible pipecause a decrease in the vertical diameter and an increase in the horizonal diameter.The horizontal movement develops a passive soil resistance that helps support thepipe. The passive soil resistance varies depending on the soil type and the degree ofcompaction of the pipe zone backfill material, native soil characteristics, cover depth,and trench width (see Table 5-3, soil classification chart). To determine E′ for a buried

Table 5-2 HS-20 and Cooper’s E-80 live loads (psi)

HS-20 Live Loads (psi) Cooper’s E-80 Live Loads (psi)

Depth WL Depth WL

ft m psi kPa ft m psi kPa 2 0.6 6 41.4 4 1.2 14.1 97.3 2.5 0.8 3.9 26.9 5 1.5 12.2 84.2 3 0.9 3.3 22.8 6 1.8 10.5 72.5 3.5 1.1 2.6 17.9 8 2.4 7.7 53.1 4 1.2 2.2 15.2 10 3.0 5.7 39.3 6 1.8 1.5 10.3 12 3.7 4.6 31.7 9 2.7 1.0 6.9 14 4.3 3.7 25.510 3.0 0.8 5.5 16 4.9 3.0 20.712 3.7 0.6 4.1 18 5.5 2.6 17.916 4.9 0.5 3.4 20 6.1 2.2 15.220 6.1 0.4 2.8 25 7.6 1.5 10.327 8.2 0.2 1.4 30 9.2 1.1 7.6

40 12.2 0.1 0.7 35 10.7 0.8 5.540 12.2 0.6 4.1

Cooper E-80 design loads consist of four 80,000-lb axles spaced 5 ft c/c. Locomotive load assumed uniformity distributed overan area 8 ft × 20 ft. Weight of track structure assumed to be 200 lb/lin ft, including impact. Height of fill measured from topof pipe to bottom of ties.



Table 5-3 Soil classification chart

Criteria for Assigning Group Symbols and Group Names Using Laboratory Testsa

Soil ClassificationGroupSymbol

Group Nameb

Coarse-grainedsoilsMore than 50%retained onNo. 200sieve

GravelsMore than50% ofcoarsefractionretained onNo. 4 sieve

Clean gravelsLess than 5%finesc

Cu ≥ 4 and 1 ≤ Cc ≤3e GW Well-graded gravelf

Cu < 4 and/or 1 > Cc > 3e GP Poorly gradedgravelf

Gravelswith finesMore than12% finesc

Fines classify as ML or MH GM Silty gravelf,g,h

Fines classify as CL orCH

GC Clayey gravelf,g,h

Sands50% ormore ofcoarsefractionpasses No. 4 sieve

Clean sandsLess than 5%finesd

Cu ≥ 6 and 1 ≤ Cc ≤ 3e SW Well-graded sandi

Cu < 6 and/or 1 >C c > 3e SP Poorly graded sandi

Sands with finesMore than12% finesd

Fines classify as ML or MH SM Silty sandg,h,i

Fines classify as CL or CH SC Clayey sandg,h,i

Fine-grainedsoils50% ormore passesthe no. 200sieve

Silts andclaysLiquidlimit lessthan 50

Inorganic PI > 7 and plots on orabove “A” line j

CL Lean clayk,l,m

PI < 4 or plots below “A”line j

ML Siltk,l,m

Organic Liquid limit—oven dried< 0.75

OL Organic clayk,l,m,n

Liquid limit—not dried Organic siltk,l,m,o

Silts andclaysLiquidlimit 50 ormore

Inorganic PI plots on or above “A”line

CH Fat clayk,l,m

PI plots below “A” line MH Elastic siltk,l,m

Organic Liquid limit—oven dried < 0.75 OH Organic clayk,l,m,p

Liquid limit—not dried Organic siltk,l,m,p

Highly organic soils Primarily organic matter, dark in color, and organic odor

PT Peat

a Based on the material passing the 3-in. (75-mm) sieve.b If field sample contained cobbles and/or boulders, add “with cobbles and/or boulders” to group name.c Gravels with 5% to 12% fines require dual symbols:

GW–GM well-graded gravel with silt GW–GC well-graded gravel with clay GP–GM poorly graded gravel with silt GP–GC poorly graded gravel with clay

d Sands with 5% to 12% fines require dual symbols: SW–SM well-graded sand with silt SW–SC well-graded sand with clay SP–SM poorly graded sand with silt SP–SC poorly graded sand with clay

e Cu = D60/D10

Cc = (D 30)2

D 10 ×D 60f If soil contains ≥ 15% sand, add “with sand” to group name.

g If fines classify as CL–ML, use dual symbol GC–GM or SC–SM.h If fines are organic, add “with organic fines” to group name.i If soil contains ≥ 15% gravel, add “with gravel” to group

name.j If the Atterberg limits (liquid limit and plasticity index)

plot in hatched area on plasticity chart, soil is a CL–ML,silty clay.

k If soil contains 15% to 29% plus No. 200, add “with sand”or “with gravel,” whichever is predominant.

l If soil contains ≥ 30% plus No. 200, predominantly sand,add “sandy” to group name.

m If soil contains ≥ 30% plus No. 200, predominantly gravel,add “gravelly” to group name.

n PI ≥ 4 and plots on or above “A” line.o PI ≤ 4 or plots below “A” line.p PI plots on or above “A” line.q PI plots below “A” line.

Source: ASTM D2487; Reprinted with permission from the Annual Book of ASTM Standards, copyright ASTM, 100 BarrHarbor Dr., West Conshohocken, PA 19428-2959.NOTE: ASTM D2487 allows the use of “borderline” symbols when test results indicate that the soil classification is close toanother group. The borderline condition is indicated by an en dash between the two symbols, for example CL–CH.



pipe, separate E′ values for the native soil, E′n, and the pipe backfill surround, E′b,must be determined and then combined using Eq 5-16. Special cases are discussedlater in this chapter.

E ′ = Sc E ′b (5-16)

Where:

E ′ = composite modulus of soil reaction, psi (to be used in Eq 5-8 and Eq 5-21)

Sc = soil support combining factor from Table 5-3, dimensionless

E ′b = modulus of soil reaction of the pipe zone embedment from Table 5-5, psi

To use Table 5-4 for Sc values, the following values must be determined:

E ′n = modulus of soil reaction of the native soil at pipe elevation from Table 5-6, psi

Bd = trench width at pipe springline, in.

5.7.4 Combined LoadingThe maximum stress or strain resulting from the combined effects of internal pressureand deflection should meet Eq 5-17 and Eq 5-18 or Eq 5-19 and Eq 5-20 as follows:

For stress basis HDB and Sb:

σpr

HDB ≤

1 −

σb rc

Sb E

FSpr

(5-17)

Table 5-4 Values for the soil support combining factor Sc

E′n/E′b Bd/D1.5

Bd/D2

Bd/D2.5

Bd/D3

Bd/D4

Bd/D5

0.1 0.15 0.30 0.60 0.80 0.90 1.000.2 0.30 0.45 0.70 0.85 0.92 1.000.4 0.50 0.60 0.80 0.90 0.95 1.000.6 0.70 0.80 0.90 0.95 1.00 1.000.8 0.85 0.90 0.95 0.98 1.00 1.001.0 1.00 1.00 1.00 1.00 1.00 1.001.5 1.30 1.15 1.10 1.05 1.00 1.002.0 1.50 1.30 1.15 1.10 1.05 1.003.0 1.75 1.45 1.30 1.20 1.08 1.00

≥5.0 2.00 1.60 1.40 1.25 1.10 1.00

NOTE: In-between values of Sc may be determined by straight-line interpolation from adjacent values.




Tabl

e 5-5

Va

lues

for

the

modul

us o

f so

il re

actio

n E

′b f

or

the

pip

e zo

ne e

mbe

dm

ent,

psi

(M

Pa)

(con

tinue

d)

Soi

l St

iffn

ess

Cat

egor

y

Soi

l T

ype

Pri

mar

y P

ipe

Zone

Bac

kfil

l M

ater

ial

(Uni

fied

Cla

ssif

icat

ion

Syst

em)*

Dum

ped

Slig

ht

<85%

Pro

ctor

<4

0%

R

elat

ive

Den

sity

Mod

erat

e 85

–95%

Pro

ctor

40

–70%

Rel

ativ

e D

ensi

ty

H

igh

>95%

Pro

ctor

>70%

Rel

ativ

e D

ensi

ty

SC

5H

ighl

y co

mpr

essi

ble

fine

-gra

ined

soi

ls (

CH

,M

H, O

L, O

H, P

T),

orbo

rder

line

soi

ls(C

H/M

H),

or a

ny d

ual

sym

bol

or b

orde

rlin

eso

il be

ginn

ing

wit

h on

eof

the

se s

ymbo

ls.

Soils

in t

his

cate

gory

req

uire

spec

ial e

ngin

eeri

ngan

alys

is t

ode

term

ine

requ

ired

dens

ity,

moi

stur

eco

nten

t, an

dco

mpa

ctiv

e ef

fort

.

Soil

s in

thi

s ca

tego

ryre

quir

e sp

ecia

len

gine

erin

g an

alys

is t

ode

term

ine

requ

ired

dens

ity,

moi

stur

e co

nten

t,an

d co

mpa

ctiv

e ef

fort

.

Soils

in t

his

cate

gory

req

uire

spec

ial e

ngin

eeri

ng a

naly

sis

tode

term

ine

requ

ired

den

sity

,m

oist

ure

cont

ent,

and

com

pact

ive

effo

rt.

Soils

in

this

cat

egor

y re

quir

e sp

ecia

len

gine

erin

g an

alys

is t

ode

term

ine

requ

ired

de

nsit

y, m

oist

ure

cont

ent,

and

com

pact

ive

effo

rt.

SC

4F

ine-

grai

ned

soil

s w

ith

med

ium

to

no p

last

icit

y(C

L, M

L, M

L–C

L),

orbo

rder

line

soi

l (M

L/C

L),

or a

ny

dual

sym

bol

orbo

rder

line

soi

lbe

ginn

ing

wit

h on

e of

thes

e sy

mbo

ls, w

ith

<30%

coa

rse-

grai

ned

part

icle

s

50

(0.3

4)20

0 (1

.4)

400

(2.8

)1,

000

(6.9

)

SC

3F

ine-

grai

ned

soil

s w

ith

med

ium

to

no p

last

icit

y(C

L, M

L, M

L–C

L),

orbo

rder

line

soi

l (M

L/C

L),

or a

ny

dual

sym

bol

orbo

rder

line

soi

lbe

ginn

ing

wit

h on

e of

thes

e sy

mbo

ls, w

ith

≥30%

coa

rse-

grai

ned

part

icle

s

100

(0.6

9)40

0 (2

.8)

1,00

0 (6

.9)

2,00

0(1

3.8)

Tabl

e co

ntin

ued

nex

t pa

ge.

NO

TE: P

erce

nt P

roct

or d

ensi

ty p

er A

ST

M D

698

and

rela

tive

den

sity

per

AS

TM

D42

53 a

nd D

4254

.V

alue

s fo

r E

′ b f

or i

n-be

twee

n so

ils

or b

orde

rlin

e P

roct

or d

ensi

ties

may

be

inte

rpol

ated

.*A

ST

M C

lass

ific

atio

n D

2487

(se

e T

able

5-3

).


Tabl

e 5-5

Va

lues

for

the

modul

us o

f so

il re

actio

n E

′b f

or

the

pip

e zo

ne e

mbe

dm

ent,

psi

(M

Pa)

(con

tinue

d)

Soi

l St

iffn

ess

Cat

egor

y

Soi

l T

ype

Pri

mar

y P

ipe

Zone

Bac

kfil

l M

ater

ial

(Uni

fied

Cla

ssif

icat

ion

Syst

em)*

Dum

ped

Slig

ht

<85%

Pro

ctor

<4

0%

R

elat

ive

Den

sity

Mod

erat

e 85

–95%

Pro

ctor

40

–70%

Rel

ativ

e D

ensi

ty

H

igh

>95%

Pro

ctor

>70%

Rel

ativ

e D

ensi

ty

SC3

Coa

rse-

grai

ned

soil

wit

hfi

nes

(GM

, GC

, SM

, SC

,G

C–G

M, G

C/S

C)

or a

nydu

al s

ymbo

l or

bord

erli

ne s

oil

begi

nnin

g w

ith

one

ofth

ese

sym

bols

,co

ntai

ning

mor

e th

an12

% f

ines

100

(0.6

9)40

0 (2

.8)

1,00

0 (

6.9)

2,00

0 (1

3.8)

SC2

Coa

rse-

grai

ned

soil

sw

ith

litt

le o

r no

fin

es(G

W, G

P, S

W, S

P, G

W–

GC

, SP

–SM

) or

any

dual

sym

bol

orbo

rder

line

soi

lbe

ginn

ing

wit

h on

e of

thes

e sy

mbo

ls,

cont

aini

ng 1

2% f

ines

or

less

200

(1.4

)1,

000

(6.9

)2,

000

(13.

8)3,

000

(20.

7)

SC1

Cru

shed

roc

k w

ith

≤15%

san

d, m

axim

um25

% p

assi

ng t

he 3

⁄ 8 in

.si

eve

and

max

imum

5%

fine

s

1,00

0 (6

.9)

3,00

0 (2

0.7)

3,00

0 (2

0.7)

3,00

0 (2

0.7)

NO

TE: P

erce

nt P

roct

or d

ensi

ty p

er A

ST

M D

698

and

rela

tive

den

sity

per

AS

TM

D42

53 a

nd D

4254

.V

alue

s fo

r E

′ b f

or i

n-be

twee

n so

ils

or b

orde

rlin

e P

roct

or d

ensi

ties

may

be

inte

rpol

ated

.*A

ST

M C

lass

ific

atio

n D

2487

(se

e T

able

5-3

).



σb rc

Sb E ≤

1 −

σpr

HDB

FSb

(5-18)

For strain basis HDB and Sb:

εpr

HDB ≤

1 −

εb rc

Sb

FSpr

(5-19)

εb rc

Sb ≤

1 −

εpr

HDB

FSb

(5-20)

Where:

prFS = pressure design factor, 1.8

FSb = bending design factor, 1.5

σpr = working stress due to internal pressure, psi

= PwD

2t

σb = bending stress due to the maximum permitted deflection, psi

Table 5-6 Values for the modulus of soil reaction E′n for the native soil at pipe zone elevation

Native in Situ Soils*

Granular Cohesive E′n (psi)

Blows/ft† Description qu(Tons/sf) Description

>0–1 very, very loose >0–0.125 very, very soft 50 1–2 very loose 0.125–0.25 very soft 200 2–4 0.25–0.50 soft 700 4–8 loose 0.50–1.0 medium 1,500

8–15 slightly compact 1.0–2.0 stiff 3,000 15–30 compact 2.0–4.0 very stiff 5,000 30–50 dense 4.0–6.0 hard 10,000 >50 very dense >6.0 very hard 20,000

*The modulus of soil reaction E ′n for rock is ≥ 50,000 psi.†Standard penetration test per ASTM D1586.

For embankment installation E ′b = E ′n = E ′ .

E′ special casesGeotextiles—When a geotextile pipe zone wrap is used, E′n values for poor soils can be greater than those shown inTable 5-6.Solid sheeting—When permanent solid sheeting designed to last the life of the pipeline is used in the pipe zone, E′ shall bebased solely on E′b.Cement stabilized sand—When cement stabilized sand is used as the pipe zone surround, initial deflections shall be basedon a sand installation and the long-term E′b = 25,000 psi. (Typical mix ratio is one sack of cement per ton or 1.5 sacks ofcement per cubic yard of mix.) For embankment installation E′b = E′n = E′.



= DfE

δd

D

tt

D

rc = rerounding coefficient, dimensionless

= 1 − Pw/435 (Pw ≤ 435 psi)

εpr = working strain due to internal pressure, in./in.

= PwD

2tEH

εb = bending strain due to maximum permitted deflection, in./in.

= Df

δd

D

tt

D

δd = maximum permitted long-term installed deflection, in.

5.7.5 Buckling5.7.5.1 Buckling theory. Buried pipe is subjected to radial external loadscomposed of vertical loads and possibly the hydrostatic pressure of groundwater andinternal vacuum, if the latter two are present. External radial pressure sufficient tobuckle buried pipe is many times higher than the pressure causing buckling of thesame pipe in a fluid environment, due to the restraining influence of the soil.

5.7.5.2 Buckling calculations. The summation of appropriate external loadsshould be equal to or less than the allowable buckling pressure. The allowablebuckling pressure qa is determined by the following equation:

qa =

1FS

[ 32Rw B′ E′ EI

D3 ]

12 (5-21)

Where:

qa = allowable buckling pressure, psi

FS = design factor, 2.5

Rw = water buoyancy factor, calculated as follows:

Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h

Where:

hw = height of water surface above top of pipe, in.

h = height of ground surface above top of pipe, in.

B′ = empirical coefficient of elastic support, dimensionless. It is calculated as follows:

B′ = 1

1 + 4e−0.065H



Where:

H = burial depth to the top of pipe, ft

E′ = composite modulus of soil reaction, psi (see Eq 5-16)

NOTE: Eq 5-21 is valid under the following conditions:

Without internal vacuum: 2 ft ≤ H ≤ 80 ft

With internal vacuum: 4 ft ≤ H ≤ 80 ft

Where internal vacuum occurs with cover depths less than 4 ft but not less than2 ft, qa in Eq 5-22 may be determined as the critical buckling pressure given by the vonMises formula. The 2 ft to 4 ft of soil cover provides a safety factor in excess of therecommended 2.5 value. In the 2-ft to 4-ft depth range, live loads plus dead loads shouldbe checked by Eq 5-23 to determine the governing required wall thickness. Themanufacturer should be consulted for further recommendations in this depth range.

The von Mises formula is:

qa =

2Ett

D (n2 − 1) (1 + K)2

+

n2 − 1 +

2n2 − 1 − vhl

1 + K

8EID3 [1 − (vhl) (vlh)]

(5-22)

Where:

n = number of lobes formed at buckling ≥ 2 (The value of n must give the minimum value of qa obtained by iterative solution.)

vhl = Poisson’s ratio, applied hoop stress

vlh = Poisson’s ratio, applied longitudinal stress

K =

2nLπD

2

Where:

L = distance between rigid ring stiffeners, in.

NOTE: For solid-wall (nonribbed) pipes, L should be the distance betweenjoints, such as bells, couplings, flanges, etc.

Typical pipe installations. Satisfaction of the buckling requirement is as-sured for typical pipe installations by using the following equation:

γw hw + Rw (Wc) + Pv ≤ qa (5-23)

Where:

γw = specific weight of water (i.e., 0.0361 lb/in.3), lb/in.3

Pv = internal vacuum pressure (i.e., atmospheric pressure less absolute pressure inside pipe), psi



In some situations, consideration of live loads in addition to dead loads may beappropriate. However, simultaneous application of live load and internal vacuumtransients need not typically be considered. If live loads are considered, satisfaction ofthe buckling requirement is ensured by:

γw hw + Rw (Wc) + WL = qa (5-24)

5.8 AXIAL LOADS _______________________________________Factors that contribute to the development of axial stresses in buried pipe are (1)hoop expansion due to internal pressure, which causes axial tensile stresses wheneverthe pipe is axially restrained; (2) restrained thermal expansion and contraction; and(3) pipe “beam” bending that may be induced by uneven bedding, differential soilsettlement, or subsidence of soil. The minimum requirements for axial strengths areas specified by Sec. 5.1.2.4 and Sec. 5.1.2.5 and Tables 11, 12, and 13 of ANSI/AWWAStandard C950. These requirements include service conditions in typical qualityunderground pipe installations that comply with the guidelines provided in chapter 6of this manual and that have thrust blocks provided at bends, blanks, and valves inaccordance with chapter 7 and pipe manufacturers’ recommendations. When re-strained joints are used, the pipe should be designed to accommodate the fullmagnitude of forces generated by internal pressure.

5.9 SPECIAL DESIGN CONSIDERATIONS ___________________Pipe that meets the design requirements of ANSI/AWWA Standard C950 and Sec. 5.7and that is installed in accordance with chapter 6 guidelines has adequate strengthfor service in usual buried applications. Special consideration should be made for thefollowing conditions: (1) elevated temperature service; (2) broad temperaturefluctuations; (3) shallow burial, where H < 4 ft (1.2 m) (Sec. 5.7.5); (4) uneven beddingor differential settlement of unstable native soils; (5) restrained tension joints; (6)extremely difficult construction conditions (for example, subaqueous installation); (7)heavy internal silt or sand loads; and (8) unusually high surface or construction loads.

5.10 DESIGN EXAMPLES _________________________________Example design calculations are presented in this section for each of three specificsituations. For reference, the set of design conditions, pipe properties, and installationparameters assumed for each design example are presented in Table 5-7. Thissummary is not repeated in the body of the example design calculations.

The pipe material properties and characteristics presented in Table 5-7 havebeen assumed for illustrative purposes and should not be used as actual designvalues. Values for these parameters differ for various pipe constructions andmaterials and should be obtained from the manufacturer.

5.10.1 Design Example 1: Stress BasisUsing the assumed set of design conditions, pipe properties, and installationparameters set forth under example 1 in Table 5-7 and following the proceduralsequence for design calculations outlined in Sec. 5.6:

1. Calculate pressure class Pc from HDB using Eq 5-1 (Sec. 5.7.1.1):



Table 5-7 Conditions and parameters for design examples

Conditions and Parameters Sec. 5.10.1(Example 1)

Sec. 5.10.2(Example 2)

Sec. 5.10.3(Example 3)

Design conditions: Nominal pipe diameter, in. 12 36 72 Working pressure Pw, psi 220 115 55 Surge pressure Ps, psi 65 55 20 Vacuum Pv, psi 14.7 8 0 Cover depth H, ft (min.–max.) 2.5–4 4–8 6–12 Wheel load P, lb 16,000 16,000 16,000 Soil-specific weight γs, lb/ft3 120 125 115 Service temperature, °F 32–100 32–90 32–95 Native soil conditions at pipe depth slightly compact

clayey sanddense silty sand medium stiff,

inorganic clay Native soil modulus E′n, psi 3,000 10,000 1,500 Groundwater table location at ground surface 3 ft below ground

surface10 ft below ground

surface Maximum hw, in. 48 60 24 Minimum hw, in. 30 12 0

Basis for HDB and Sb Stress, psi Strain, in./in. Strain, in./in.

Pipe properties: Trial pressure class Pc, psi 250 150 100 Reinforced wall thickness t, in. 0.21 0.61 0.61 Liner thickness tL, in. 0 0.04 0.05 Total wall thickness tt, in. 0.21 0.65 0.66 Minimum pipe stiffness F/ ∆y, psi 72 36 9 Hoop tensile modulus EH, psi 3.3E6 1.8E6 3.25E6 Hoop flexural modulus E, psi 3.45E6 1.9E6 3.5E6 HDB 14,800 0.0064 0.0058 Sb 0.0100 0.0115 0.0058 Mean diameter D, in. 12.21 36.69 72.71 Distance between joints L, in. 240 360 480 Poisson’s ratio v, in./in. Hoop load vhL 0.35 0.30 0.35 Axial load vih 0.15 0.20 0.15

Installation parameters: Pipe/zone installation description slightly compacted

silty sand, SMmoderately compacted

clayey sand, SCmoderately

compacted gravel, GWTrench width, in. 27 58 104 Shape factor Df 3.5 5.5 7.0 Backfill soil modulus E′b, psi 400 1,000 2,000 Deflection coefficient Kx 0.1 0.1 0.1 Deflection lag factor DL 1.05 1.1 1.2

Deflection: Maximum deflection permitted, δd/D 0.05 0.05 0.05



Pc = 250 psi ≤

HDBFS

2tD

≤

14,8001.8

2(0.21)12.21

≤ 282.83 psi ∴ OK

2. Check working pressure Pw using Pc and Eq 5-3 (Sec. 5.7.1.2):

Pc ≥ Pw

250 psi ≥ 220 psi ∴ OK

3. Check surge pressure Ps using Pc and Eq 5-4:

Pc ≥ (Pw + Ps) / 1.4

250 ≥ (220 + 65) / 1.4

250 psi ≥ 204 psi ∴ OK

4. Calculate allowable deflection, ∆ya, from ring bending using Eq 5-5 (Sec. 5.7.2):

σb = Df (E)

∆ya

D

tt

D ≤

E Sb

FS

3.5 (3.45E6)

∆ya

12.21

0.2112.21

≤

(3.45E6) (0.01)1.5

17,009 ∆ya ≤ 23,000

Therefore, maximum ∆ya = 1.35 in.From Eq 5-8 (Sec. 5.7.3):

∆ y

D ≤

δ d

D ≤

∆ ya

D

In this example, δd/D = 0.05:

∆ y/ D ≤ 0.05 ≤ 1.35/12.21

(5%) D ≤ (11%) D ∴ OK

5. Calculate external loads Wc and WL:

Determine external load Wc using Eq 5-9:



Wc = γs H

144

For H = 2.5 ft Wc = 120 (2.5 ft)

144 = 2.08 psi

For H = 4 ft Wc = 120 (4 ft)

144 = 3.33 psi

Determine external load WL using Eq 5-13:

WL = P (If) / [ 144 (L1) (L2) ]

Solution of Eq 5-13 for WL requires determining If, L1, and L2:

For H = 2.5 ft If = 1.1

For H = 4 ft If = 1.0

L1 is determined from Eq 5-10:

L1 = 0.83 + 1.75 (H)

For H = 2.5 ft L1 = 0.83 + 1.75 (2.5 ft) = 5.21 ft

For H = 4 ft L1 = 0.83 + 1.75 (4 ft) = 7.83 ft

Compute L2 using Eq 5-12:

H ≥ 2.48 ft L2 = [ (43.67) + 1.75 (H) ]/8

For H = 2.5 ft L2 = [ (43.67) + 1.75 (2.5 ft) ] / 8 = 6.01 ft

For H = 4 ft L2 = [ (43.67 ) + 1.75 (4 ft) ] /8 = 6.33 ft

Substituting in Eq 5-13:

For H = 2.5 ft WL = 16,000 (1.1)/[144 (5.21) (6.01)] = 3.90 psi

For H = 4 ft WL = 16,000 (1.0)/[144 (7.83) (6.33)] = 2.24 psi

6. Calculate the composite modulus of soil reaction E′ using Eq 5-16:

E′ = Sc E′b

In order to determine E′, first determine Sc:

E′n/E′b = 3,000 / 400 = 7.5

Bd/D = 27/12.21 = 2.21



Using Table 5-4, by interpolation Sc = 1.52:Substituting in Eq 5-16:

E′ = 1.52 (400) = 608 psi

7. Calculate deflection using Eq 5-8 (Sec. 5.7.3):

∆y

D =

(DL Wc + WL) KX

0.149 PS + 0.061 E′ 3 100%

Substituting in Eq 5-8 for H = 2.5 ft:

∆y

D =

(1.05 × 2.08 + 3.90) (0.1) 0.149 (72) + 0.061 (608)

× 100 = 1.27 %

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D

1.27% ≤ 5% ≤ 11% ∴ ΟΚ

Substituting in Eq 5-8 for H = 4 ft:

∆y

D =

(1.05 × 3.33 + 2.24) (0.1)[ (0.149 (72) + 0.061 (608) ]

× 100

= 1.20 %

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D

1.20% ≤ 5% ≤ 11% ∴ OK

8. Check combined loading stress δc using Eq 5-17 and Eq 5-18 (Sec. 5.7.4):

Check using Eq 5-17:

σpr

HDB ≤

1 −

σb rc

E Sb

FSpr

220 (12.21)2 (0.21)

14,800

≤

1 −

(3.5) (3.45E6)0.01 (3.45E6)

(0.05)

0.2112.21

1−

220435

1.8

0.43 ≤ 0.47 ∴ OK




σb rc

ESb ≤

1 −

σpr

HDB

FSb

(3.5) (3.45E6) (0.05)

0.2112.21

1 −

220435

(3.45E6) (0.01) ≤

1 −

(220) (12.21)(2) (0.21)

14,800

1.5

0.15 ≤ 0.38

9. Check buckling pressure.NOTE: Vacuum load is present. Determine the allowable buckling pressure qa for

H = 2.5 ft, using Eq 5-22:

qa =

2Ett

D (n2 − 1) (1 + K)2

+

n2 − 1 +

2n2 − 1 − vhl

1 + K

8EI

D3 [1 − (vhl) (vlh) ]

Solution of Eq 5-22 for qa requires determination of value of K:

K =

2nLπD

2

=

2 (2) (240)π(12.21)

2

= 626.3

Substituting in Eq 5-22 and solving for qa:

qa =

2 (3.45E6) (0.21)

(12.21) (22 − 1) (1 + 626.3)2

+

22 − 1 +

2 (22) − 1 − 0.35

1 + 626.3

(8) (3.45E6) (0.213/12)

(12.21)3 [1 − (0.35) (0.15) ]

= 0.101 + 3.011 (12.35) = 37.29 psi

Determine the allowable buckling pressure, qa, for H = 4 ft, using Eq 5-21:

qa = 1

FS

32Rw B ′E ′

EI

D3

0.5

Solution of Eq 5-21 for qa requires determination of values for Rw and B′:

Rw = 1 − 0.33 (hw/h)



= 1 − 0.33 (48/48)

= 0.67

B ′ = 1/(1 + 4e−0.065 H)

= 1/ (1 + 4e−0.26 )

= 0.245

Substituting the values of Rw and B′ in Eq 5-21:

qa = 1

2.5

32 (0.67) (0.245) (608)

3.45E 6 (0.21)3

12 (12.21)3

0.5

= 27.34 psi

To satisfy the buckling requirement for normal pipe installation, use Eq 5-23:

γw (hw) + Rw Wc + Pv ≤ qa

In situations where consideration of live loads is appropriate, use Eq 5-24:

γw (hw) + Rw Wc + WL ≤ qa

Solutions of Eq 5-23 and Eq 5-24 both require determination of the valueof the water buoyancy factor Rw at 2.5 ft depth also:

Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h

= 1 − 0.33 (30/30)

= 0.67

Substituting in Eq 5-23 to check normal pipe installation condition with H = 2.5 ft:

(0.0361) (30) + 0.67 (2.08) + 14.7 ≤ 32.29 psi

17.18 ≤ 32.29 psi ∴ OK

and substituting in Eq 5-24 to check live load condition with H = 2.5 ft:

(0.0361) (30) + (0.67) (2.08) + (3.9) ≤ 32.29 psi

6.38 ≤ 32.29 psi ∴ OK

Substituting in Eq 5-23 to check normal pipe installation condition with H = 4 ft: (0.0361) (48) + 0.67 (3.33) + (14.7) ≤ 27.34 psi

18.66 ≤ 27.34 psi



and substituting in Eq 5-24 to check live load condition with H = 4 ft:

(0.0361) (48) + 0.67 (3.33) + (2.24) ≤ 27.34 psi

6.20 ≤ 27.34 psi ∴ OK

Conclusion: Design is OK since all checks are satisfied.

5.10.2 Design Example 2: Strain BasisUsing the assumed set of design conditions, pipe properties, and installationparameters set forth under example 2 in Table 5-7 and following the proceduralsequence for design calculations outlined under Section 5.6:

1. Calculate pressure class Pc from HDB using Eq 5-2 (Sec. 5.7.1.1.):

Pc = 150 psi ≤

HDBFS

2EHt

D

≤

0.00641.8

2 (1.8E6) (0.61)36.69

≤ 212.81 psi ∴ OK


Pc ≥ Pw

150 psi ≥ 115 psi ∴ OK

3. Check surge pressure Ps using Pc and Eq 5-4 (Sec. 5.7.1.3):

Pc ≥ (Pw + Ps) /1.4

150 ≥ (115 + 55) /1.4

150 psi ≥ 122 psi ∴ OK

4. Calculate allowable deflection, ∆ya, from ring bending using Eq 5-6 (Sec. 5.7.2):

εb = Df

∆ya

D

tt

D ≤

Sb

FS

5.5

∆ya

36.69

0.6536.69

≤

0.01151.5

0.00266 ∆ ya ≤ 0.00767

Therefore, maximum ∆ya = 2.89 in.



From Eq 5-7 (Sec. 5.7.3.):

∆y

D ≤

δd

D ≤

δya

D

In this example, δd

D = 0.05

∆y

D ≤ 0.05 ≤

2.8936.69

5% ≤ 7.9% ∴ OK

5. Calculate loads Wc and WL:

Determine external load Wc using Eq 5-9 (Sec. 5.7.3.5):

Wc = γs H

144

For H = 4 ft Wc = 125 (4)

144 = 3.47 psi

For H = 8 ft Wc = 125 (8)

144 = 6.94 psi

Determine external load WL using Eq 5-13 (Sec. 5.7.3.6):

WL = P (If) / [144 (L1) (L2) ]


For H = 4 ft If = 1.0

For H = 8 ft If = 1.0


L1 = 0.83 + 1.75 (H)

For H = 4 ft L1 = 0.83 + 1.75 (4) = 7.83 ft

For H = 8 ft L1 = 0.83 + 1.75 (8) = 14.83 ft


H ≤ 2.48 ft L2 = (43.67 + 1.75 (H) ) /8

For H = 4 ft L2 = (43.67 + 1.75 (4) ) /8 = 6.33 ft

For H = 8 ft L2 = (43.67 + 1.75 (8) ) / 8 = 7.21 ft




For H = 4 ft WL = 16,000 (1.0) / [144 ( 7.83) (6.33) ] = 2.24 psi

For H = 8 ft WL = 16,000 (1.0) / [144 (14.83) (7.21)] = 1.04 psi

6. Calculate the composite modulus of soil reaction E′, using Eq 5-16 (Sec. 5.7.3):

E ′ = Sc E′b

First determine Sc:

En′ / Eb′ = 10,000 / 1,000 = 10

Bd / D = 58 / 36.69 = 1.58

Using Table 5-4, by interpolation Sc = 1.94 Substituting in Eq 5-16:

E′ = (1.94 (1,000) ) = 1,940 psi


∆y

D =

(DL Wc + WL) Kx

0.149 PS + 0.061 E′ × 100%


∆y

D =

(1.1 (3.47) + 2.24) 0.1

0.149 (36) + 0.061 (1,940) × 100%

= 0.49 %

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D

0.49 % ≤ 5 % ≤ 7.9% ∴ OK


∆yD

=

(1.1 (6.94) + 1.04) 0.1

0.149 (36) + 0.061 (1,940) × 100%

= 0.70%

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D



0.70% ≤ 5% ≤ 7.9% ∴ OK

8. Check combined loading strain, εc, using Eq 5-19 and Eq 5-20:


εpr

HDB ≤

1 −

εb rc

Sb

FSpr

(115) (36.69)2 (0.61) (1.8E6)

0.0064 ≤

1 −

(5.5) (0.05)

0.6536.69

1 −

115435

0.0115

1.8

0.30 ≤ 0.38 ∴ OK


εb rc

Sb ≤

1 −

εpr

HDB

FSb

(5.5) (0.05)

0.6536.69

1 −

115435

0.0115

≤

1 −

(115) (36.69)2 (0.61) (1.8E6)

0.0064

1.5

0.31 ≤ 0.47 ∴ OK

9. Check buckling using Eq 5-21:

qa = 1

FS

32Rw B ′ E ′

EID3

0.5

Solution of Eq 5-21 for qa requires determination of values for Rw and B′:

Rw = 1 − 0.33 (hw/h); 0 ≤ hw ≤ h

For H = 8 ft:

Rw k = 1 − 0.33 (60/96)

= 0.794



For H = 4 ft:

Rw = 1 − 0.33 (12/48)

= 0.917

B ′ = 1

1 + 4e−0.065(H)

For H = 8 ft:

B ′ = 1

1 + 4e−0.065(8)

= 0.296

For H = 4 ft:

B ′ = 1

1 + 4e−0.065 (4)

= 0.245

Substituting the values of Rw and B′ in Eq 5-21 for H = 8 ft:

qa = 1

2.5

32 (0.794) (0.296) (1,940)

1.9E6 (0.61)3

12 (36.69)3

0.5

= 41.21 psi


qa = 1

2.5

32 (0.917) (0.245) (1,940)

1.9E6 (0.61)3

12 (36.69)3

= 40.30 psi

Check to satisfy the requirements of Eq 5-23:

γw hw + Rw Wc + Pv ≤ qa

and Eq 5-24:

γw hw + Rw Wc + WL ≤ qa


(0.0361) (60) + (0.794) (6.94) + 8 ≤ 41.21 psi

15.68 psi ≤ 41.21 psi



and in Eq 5-24:

(0.0361) (60) + (0.794) (6.94) + 1.04 ≤ 41.21 psi

8.72 psi ≤ 41.21 psi ∴ OK


(0.0361) (12) + (0.917) (3.47) + 8 ≤ 40.30 psi

11.62 psi ≤ 40.30 psi

and in Eq 5-24:

(0.0361) (12) + (0.917) (3.47) + 2.24 ≤ 40.30 psi

5.86 psi ≤ 40.30 psi ∴ OK


5.10.3 Design Example 3: Strain BasisUsing the assumed set of design conditions, pipe properties, and installationparameters set forth in example 3 in Table 5-7 and following the procedural sequencefor design calculations outlined in Sec. 5.6:

1. Calculate pressure class Pc from HDB using Eq 5-2 (Sec. 5.7.1):

Pc = 100 psi ≤

HDBFS

2EHt

D

≤

0.00581.8

2 (3.25E6) (0.61)72.71

≤ 175.713 psi ∴ OK


Pc ≥ Pw

100 psi ≥ 55 psi ∴ OK

3. Check surge pressure Ps using Pc and Eq 5-4 (Sec. 5.7.1.3):

Pc ≥ (Pw + Ps)/1.4

100 ≥ (55 + 20)/1.4

100 psi ≥ 54 psi ∴ OK



4. Calculate allowable deflection ∆ya from ring bending using Eq 5-6 (Sec. 5.7.2):

εb = Df

∆ya

D

tt

D ≤

Sb

FS

7.0

∆ya

72.71

0.6672.71

≤

0.00581.5

0.00087884 ∆ya ≤ 0.0038666

∴ Maximum ∆ ya = 4.42 in.

From Eq 5-7 (Sec. 5.7.3):

∆ y

D ≤

δ d

D ≤

∆ ya

D

In this example:

δ d

D = 0.05

∆y/d ≤ 0.05 ≤ 4.4272.71

(5%) D ≤ (6.09%) D ∴ OK

5. Calculate external loads Wc and WL.

Determine external load Wc using Eq 5-9 (Sec. 5.7.3.5):

Wc = γs H

144

For H = 6 ft Wc = 115 (6 ft)

144 = 4.79 psi

For H = 12 ft Wc = 115 (12 ft)

144 = 9.58 psi

Determine external load WL using Eq 5-13 (Sec. 5.7.3.6):

WL = P (If)/[ 144 (L1) (L2) ]


For H = 6 ft If = 1.0

For H = 12 ft If = 1.0


L1 = 0.83 + 1.75 (H)



For H = 6 ft L1 = 0.83 + 1.75 (6 ft) = 11.33 ft

For H = 12 ft L1 = 0.83 + 1.75 (12 ft) = 21.83 ft


For H ≥ 2.48 ft L2 = (43.67 + 1.75 (H) ) /8

For H = 6 ft L2 = (43.67 + 1.75 (6 ft) ) /8 = 6.77 ft

For H = 12 ft L2 = (43.67 + 1.75 (12 ft) ) /8 = 8.08 ft


For H = 6 ft WL = 16,000 (1.0)/[144 (11.33) (6.77) ] = 1.45 psi

For H = 12 ft WL = 16,000 (1.0)/[144 (21.83) (8.08) ] = 0.63 psi

6. Calculate the composite modulus of soil reaction E′, using Eq 5-16 (Sec. 5.7.3.8):

E ′ = Sc E ′b

First determine Sc:

En′/ Eb′ = 1,500/2,000 = 0.75

Bd/D = 104/72.71 = 1.4303

Using Table 5-4, by interpolation Sc = 0.81:


E ′ = 0.81 (2,000) = 1,620 psi


∆y

D =

( DL Wc + WL) Kx

0.149 PS + 0.061 E ′ × 100%


∆y

D =

(1.2 (4.79) + 1.45) 0.1

0.149 (9) + 0.061 (1,620) × 100%

= 0.72 %

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D

0.72% ≤ 5% ≤ 6.09% ∴ OK




∆y

D =

(1.2 ( 9.58) + (0.63) ) 0.1

0.149 (9) + 0.061 (1,620) × 100%

= 1.21 %

Check using Eq 5-7:

∆y

D ≤

δd

D ≤

∆ya

D

1.21% ≤ 5% ≤ 6.09% ∴ OK

8. Check combined loading strain, εc, using Eq 5-19 and Eq 5-20:


εpr

HDB ≤

1 −

εbrc

Sb

FSpr

(55) (72.71)2 (0.61) (3.25E6)

0.0058 ≤

1 −

7 (0.05)

0.6672.71

(1 −

55435

)

0.0058

1.8

0.17 ≤ 0.29 ∴ OK


εb rc

Sb ≤

1 − (εpr

HDB)

FSb

( 0.6672.71

) (0.05) (7.0) (1 − 55435

)

0.0058 ≤

1 −

(55) (72.71)(2) (0.61) (3.25E6)

0.0058

1.5

0.48 ≤ 0.55 ∴ OK

9. Check allowed buckling pressure using Eq 5-21:

qa = 1

FS

32Rw B ′E ′

EI

D3

12



Solution of Eq 5-21 requires determination of Rw and B′:

Rw = 1 − 0.33 (hw/h)

For H = 6 ft

Rw = 1 − 0.33 (0/72)

= 1.0

For H = 12 ft

Rw = 1 − 0.33 (24/144)

= 0.945

B ′ = 1

1 + 4e−0.065H

For H = 6 ft

B ′ =

1

1 + 4e−0.065 (6)

= 0.270

For H = 12 ft

B ′ = 1

1 + 4e−0.065 (12)

= 0.353


qa = 1

2.5

32 (1.0) (0.270)

(1,620) 3.5E6 (0.613)

(12) 72.71 3

0.5

= 19.64 psi


qa = 1

2.5

32 (0.945) (0.353)

(1,620) 3.5E6 (0.613)

(12) 72.713

0.5

= 21.83 psi

Since no vacuum is present, check to satisfy the requirements of Eq 5-24 only:

qa ≥ WL + Rw (Wc) + γw hw



Substituting for H = 6 ft:

≥ (1.45) + (1) (4.79) + 0.0361 (0 in.) = 6.24 ≤ 19.64 ∴OK

Substituting for H = 12 ft:

≥ (0.63) + 0.945 (9.58) + 0.0361 (24)

= 10.55 ≤ 21.83 ∴ OK


REFERENCES _____________________________________________AASHTO H-20. Washington, D.C.: Ameri-

can Association of State Highway andTransportation Officials.

Cagle, L., and B.C. Glascock. 1982. Recom-mended Design Requirements for Elas-tic Buckling of Buried Flexible Pipe(Report of ANSI/AWWA Standard C950Ad-Hoc Task Group on Buckling). InProc. of AWWA Annual Conference andSPI 39th Annual Conference (January,1984). Denver, Colo.: American WaterWorks Association.

Luscher, U. 1966. Buckling of Soil Sur-rounded Tubes. Jour. Soil Mech. &Found., 92(6):213.

Molin, J. 1971. Principles of Calculation forUnderground Plastic Pipes—Calcula-tions of Loads, Deflection, Strain. ISOBull., 2(10):21.

Spangler, M.G. and R.L. Handy. 1982. SoilEngineering. New York: Harper & Row.

Standard Classification of Soils for Engi-neering Purposes (Unified Soil Classi-fication System.) 1993. ASTM D2487.West Conshohocken, Pa: American So-ciety for Testing and Materials.


Standard Practice for Determining Dimen-sions of ‘Fiberglass’ (Glass-Fiber-Rein-forced Thermosetting Resin) Pipe andFittings. 1991. ASTM D3567. WestConshohocken, Pa.: American Societyfor Testing and Materials.

Standard Test Method for Determination ofExternal Loading Characteristics ofPlastic Pipe by Parallel-Plate Load-ing. 1993. ASTM D2412. West Con-shohocken, Pa.: American Society forTesting and Materials.

Standard Test Method for Minimum IndexDensity and Unit Weight of Soils andCalculation of Relative Density. 1991.ASTM D4254. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Test Method for Penetration Testand Split-Barrel Sampling of Soils.1984. ASTM D1586. West Consho-hocken, Pa.: American Society forTesting and Materials.

Standard Test Methods for Maximum IndexDensity and Unit Weight of Soils Usinga Vibratory Table. 1993. ASTM D4253.West Conshohocken, Pa.: American So-ciety for Testing and Materials.

Test Method for Laboratory CompactionCharacteristics of Soil Using StandardEffort. 1991. ASTM D698. West Con-shohocken, Pa.: American Society forTesting and Materials.

Von Mises, R. 1914. Critical Pressure of Cy-lindrical Tubes. Zertschorft des VereinsDeutscher Ingenieure, 28:19.



Guidelines for UndergroundInstallation of Fiberglass Pipe

GUIDELINES FOR UN DERGROUND INSTALLATION OF FIBERGLASS PIPE

6.1 INTRODUCTION ______________________________________The structural and installation designs of fiberglass pipe, or almost any buried pipe,are closely related. The structural design process, discussed in chapter 5, assumesthat a pipe will receive support from the surrounding soil, and the installation processmust ensure that the support is provided. The guidelines in this chapter suggestprocedures for burial of fiberglass pipe in typically encountered soil conditions.Recommendations for trenching, placing, and joining pipe; placing and compactingbackfill; and monitoring deflection levels are included.

ANSI/AWWA Standard C950 specifies pipe that encompass a wide range ofproduct variables. Diameters range from 1 in. to 12 ft., pipe stiffnesses range from9 psi to 72 psi (62 kPa to 496 kPa), and internal pressure ratings range up to 250 psi(1,724 kPa). Designers and installers should recognize that all possible combinationsof pipe, soil types, and natural ground conditions that may occur are not consideredin this chapter. The recommendations provided may need to be modified or expandedto meet the needs of some installation conditions. Section 6.9 lists areas that may beinfluenced by project, local, or regional conditions and should be given considerationwhen preparing specifications. Guidance for installation of fiberglass pipe insubaqueous conditions is not included.

AWWA MANUAL M45

Chapter 6

73


These guidelines are for use by designers and specifiers, manufacturers,installation contractors, regulatory agencies, owners, and inspection organizationsthat are involved in the construction of buried fiberglass pipelines.

6.2 RELATED DOCUMENTS _______________________________The following are several ASTM standards that provide engineers with additionalinformation related to installing buried pipe.

D8 Standard Terminology Relating to Materials for Roads andPavements

D420 Standard Guide to Site Characterization for Engineering,Design, and Construction Purposes

D653 Standard Terminology Relating to Soil, Rock, and ContainedFluids

D698 Test Method for Laboratory Compaction Characteristics of SoilUsing Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)

D883 Standard Terminology Relating to PlasticsD1556 Standard Test Method for Density and Unit Weight of Soil in

Place by the Sand-Cone MethodD1557 Test Method for Laboratory Compaction Characteristics of Soil

Using Modified Effort (56,000 ft-lbf/ft [2,700 kN-m/m])D2167 Standard Test Method for Density and Unit Weight of Soil in

Place by the Rubber Balloon MethodD2216 Standard Test Method for Laboratory Determination of Water

(Moisture) Content of Soil and RockD2321 Standard Practice for Underground Installation of Thermo-

plastic Pipe for Sewers and Other Gravity-Flow ApplicationsD2412 Standard Test Method for Determination of External Loading

Characteristics of Plastic Pipe by Parallel-Plate LoadingD2487 Standard Classification of Soils for Engineering Purposes

(Unified Soil Classification System)D2488 Standard Practice for Description and Identification of Soils

(Visual–Manual Procedure)D2922 Standard Test Methods for Density of Soil and Soil-Aggregate

in Place by Nuclear Methods (Shallow Depth)D3017 Standard Test Method for Water Content of Soil and Rock in

Place by Nuclear Methods (Shallow Depth)D3839 Standard Practice for Underground Installation of “Fiberglass”

(Glass-Fiber-Reinforced Thermosetting-Resin) PipeD4253 Standard Test Methods for Maximum Index Density and Unit

Weight of Soils Using a Vibratory TableD4254 Standard Test Method for Minimum Index Density and Unit

Weight of Soils and Calculation of Relative DensityD4318 Standard Test Method for Liquid Limit, Plastic Limit, and

Plasticity Index of SoilsD4564 Standard Test Method for Density of Soil in Place by the

Sleeve MethodD4643 Standard Test Method for Determination of Water (Moisture)

Content of Soil by the Microwave Oven MethodD4914 Standard Test Methods for Density of Soil and Rock in Place

by the Sand Replacement Method in a Test Pit



D4944 Standard Test Method for Field Determination of Water(Moisture) Content of Soil by the Calcium Carbide GasPressure Tester Method

D4959 Standard Test Method for Determination of Water (Moisture)Content of Soil by Direct Heating Method

D5030 Standard Test Method for Density of Soil and Rock in Place bythe Water Replacement Method in a Test Pit

D5080 Standard Test Method for Rapid Determination of PercentCompaction

F412 Standard Terminology Relating to Plastic Piping Systems

6.3 TERMINOLOGY ______________________________________Terminology used in this chapter is in accordance with ASTM Standards F412, D8,D653, and D883, unless otherwise indicated. The following terms are specific to thismanual.

Bedding. Backfill material placed in the bottom of the trench or on thefoundation to provide a uniform material on which to lay the pipe; the bedding mayor may not include part of the haunch zone (see Figure 6-1).

Compactibility. A measure of the ease with which a soil may be compacted toa high density and high stiffness. Crushed rock has high compactibility because adense and stiff state may be achieved with little compactive energy.

Deflection. Any change in the diameter of the pipe resulting from installationand imposed loads. Deflection may be measured and reported as either vertical orhorizontal and is usually expressed as a percentage of the undeflected pipe diameter.

ExcavatedTrench Width

FinalBackfill

6 to 12 in.

Backfill

InitialBackfill

In Situ Soil(native)

In Situ Soil(native)

Pipe ZoneEmbedment

Foundation(if required)

HaunchZone

Bedding

Reprinted with permission from the Annual Book of ASTM Standards, Copyright ASTM, 100 Barr HarborDr., West Conshohocken, PA 19428-2959.

Figure 6-1 Trench cross-section terminology

GUIDELINES FOR UNDERGROUND INSTALLATION OF FIBERGLASS PIPE 75


Engineer. The engineer in responsible charge of the work or the dulyrecognized or authorized representative.

Final backfill. Backfill material placed from the top of the initial backfill tothe ground surface.

Foundation. Backfill material placed and compacted in the bottom of thetrench to replace over excavated material and/or to stabilize the trench bottom ifunsuitable ground conditions are encountered (see Figure 6-1).

Geotextile. Any permeable textile material used with foundation, soil, earth,rock, or any other geotechnical engineering related material, as an integral part of asynthetic product, structure, or system.

Haunching. Backfill material placed on top of the bedding and under thespringline of the pipe; the term only pertains to soil directly beneath the pipe (seeFigure 6-1).

Initial backfill. Backfill material placed at the sides of the pipe and up to 6 in.to 12 in. (150 mm to 300 mm) over the top of the pipe, including the haunching (seeFigure 6-1).

Manufactured aggregates. Aggregates such as slag that are products orby-products of a manufacturing process, or natural aggregates that are reduced totheir final form by a manufacturing process such as crushing.

Maximum standard Proctor density. The maximum dry density of soilcompacted at optimum moisture content and with standard effort in accordance withASTM D698.

Native (in situ) soil. Natural soil in which a trench is excavated for pipeinstallation or on which a pipe and embankment are placed.

Open-graded aggregate. An aggregate that has a particle size distributionsuch that, when compacted, the resulting voids between the aggregate particles arerelatively large. The voids are expressed as a percentage of the total space occupiedby the material.

Optimum moisture content. The moisture content of soil at which itsmaximum density is obtained when compacted with standard effort (see ASTM D698).

Pipe zone embedment. All backfill around the pipe, including the bedding,haunching, and initial backfill.

Processed aggregates. Aggregates that are screened, washed, mixed, orblended to produce a specific particle size distribution.

Relative density. A measure of the density of a granular soil based on theactual density of the soil “relative” to the soil in its loosest state and the soil in itsdensest state (see ASTM D653 for a precise definition) as obtained by laboratorytesting in accordance with ASTM D4253 and D4254.

Soil stiffness. A property of soil, generally represented numerically by amodulus of deformation, that indicates the relative amount of deformation that willoccur under a given load.

Split installation. An installation where the initial backfill is composed of twodifferent materials or one material placed at two different densities. The primaryinitial backfill extends from the top of the bedding to a depth of at least 0.5 times thediameter, and the secondary initial backfill extends from the top of the primarybackfill to the top of the initial backfill.



6.4 IN SITU SOILS _______________________________________It is important to understand in situ conditions prior to construction in order toprepare proper specifications and planning construction methods. Classification ofsoils according to ASTM D2487 and D2488 is useful in gaining an understanding of insitu conditions. Other tests, such as the standard penetration test, are also useful indetermining soil stiffness. Depending on actual installation conditions, such as trenchgeometry, the in situ soil conditions may also have a significant impact on pipedesign. Refer to chapter 5 for further discussion.

Consideration should also be given to seasonal variations in groundwater levelwhen evaluating groundwater conditions. For example, if the soil exploration programis conducted in August, the groundwater level may be quite low compared to levels inApril or May.

6.5 EMBEDMENT MATERIALS ____________________________Soil types used or encountered in burying pipes include those classified in Table 5-3,and natural, manufactured, and processed aggregates. The soil classifications aregrouped into soil “stiffness categories” (SC) in Table 6-1, based on the typical soilstiffness when compacted. Soil SC1 indicates a soil with high compatibility, i.e., a soilthat provides the highest soil stiffness at any given percentage of maximum Proctordensity and a soil that provides a given soil stiffness with the least compactive energy.Each higher number soil stiffness category is successively less compatible, i.e., itprovides less soil stiffness at a given percentage of maximum Proctor density andrequires greater compactive energy to provide a given level of soil stiffness. Seechapter 5 for a discussion of how soil stiffness affects buried pipe behavior.

Table 6-2 provides recommendations on installation and use of embedmentmaterials based on stiffness category and location in the trench. In general, soilconforming to SC1 through SC4 may be used as recommended unless otherwisespecified, but SC5 materials should be excluded from the pipe zone embedment.

6.5.1 Soil Stiffness ClassesSoil stiffness category 1 (SC1). SC1 materials provide maximum pipe support fora given density due to low content of sand and fines. With minimum effort thesematerials can be installed at relatively high soil stiffnesses over a wide range ofmoisture contents. In addition, the high permeability of SC1 materials may aid in thecontrol of water and are often desirable for embedment in rock cuts where water isfrequently encountered. However, when groundwater flow is anticipated, considera-tion should be given to the potential for migration of fines from adjacent materialsinto the open-graded SC1 materials. Refer to Sec. 6.5.2 for a discussion of use of soilin backfill.

Soil stiffness category 2 (SC2). SC2 materials, when compacted, provide arelatively high level of pipe support; however, open-graded groups may allowmigration and the sizes should be checked for compatibility with adjacent material;see Sec. 6.5.2.

Soil stiffness category 3 (SC3). SC3 materials provide less support for agiven density than SC1 or SC2 materials. Higher levels of compactive effort arerequired and moisture content must be controlled. These materials provide reasonablelevels of pipe support once proper density is achieved.

Soil stiffness category 4 (SC4). SC4 materials require a geotechnicalevaluation prior to use. The moisture content must be near optimum to minimize



compactive effort and achieve the required density. When properly placed andcompacted, SC4 materials can provide reasonable levels of pipe support; however,these materials may not be suitable under high fills, surface applied wheel loads, orhigh energy level vibratory compactors and tampers. Do not use where waterconditions in the trench prevent proper placement and compaction.

6.5.2 Considerations for Use of Soil in BackfillMoisture content of embedment materials. The moisture content of embedmentmaterials with substantial fines must be controlled to permit placement andcompaction to required levels. For nonfree draining soils (i.e., SC3, SC4, and somedual symbol SC2 soils), moisture content is typically controlled to plus or minus3 percent of optimum (ASTM D698). Obtaining and maintaining the required limitson moisture content is an important criterion for selecting materials, because failureto achieve required density, especially in the pipe zone, may result in excessivedeflection. SC1 and most SC2 materials are free draining and require little or nocontrol of moisture for compaction.

Maximum particle size. Maximum particle size for the pipe embedment zoneis limited to material passing a 11⁄2-in. (40-mm) sieve. To enhance placement aroundsmall diameter pipe, typically 15 in. (375 mm) and smaller, or to prevent damage tothe pipe wall, a smaller maximum size should be used. A rule often applied is that themaximum particle size should not exceed three times the pipe wall thickness.Individual manufacturers generally offer recommendations on maximum particle sizeallowed when installing their products. When final backfill contains rocks, cobbles,etc., the engineer should consider initial backfill cover levels greater than the 6 in. to12 in. (150 mm to 300 mm) shown in Figure 6-1.

Migration. When open-graded material is placed adjacent to a finer material,fines may migrate into the coarser material under the action of hydraulic gradientfrom groundwater flow. Significant hydraulic gradients may arise in the pipeline

Table 6-1 Soil stiffness categories

Soil Group Soil Stiffness Category*,†

Crushed rock and gravel with <15% sand ≤ 5% fines SC1

GW, GP, SW, SP, dual symbol soils containing one of these designationssuch as GW–GC containing 12% fines or less

SC2

GM, GC, SM, SC with more than 12% fines; and ML, CL, or borderlinesoils beginning with one of these designations, such as ML/CL, with30% or more retained on the No. 200 sieve

SC3

ML, CL, or borderline soil beginning with one of these designations,such as ML/MH, with less than 30% retained on the No. 200 sieve

SC4

CH, MH, OL, OH, PT, CH/MH, and any frozen materials SC5*Soil stiffness categories group soil types together as a function of the relative soil stiffness developed when compacted to agiven level. At any given level of compaction, SC1 soils provide the highest stiffness and SC5 soils provide the loweststiffness.†The soil stiffness categories are similar but not identical to the soil classes in ASTM D2321.Reprinted with permission from the Annual Book of ASTM Standards, Copyright ASTM, 100 Barr Harbor Dr., WestConshohocken, PA 19428-2959.



Table 6-2 Recommendations for installation and use of soils and aggregates for foundationand pipe zone embedmenta

SC1 SC2 SC3 SC4

General Recommendationsand Restrictions

Acceptable andcommon where nomigration isprobable or whencombined with ageotextile filtermedia. Suitable foruse as a drainageblanket andunderdrain whereadjacent materialsare suitably gradedor when used with ageotextile filterfabric (seeSec. 6.5.2).

Where hydraulicgradient exists,check gradation tominimizemigration. Cleangroups are suitablefor use as drainageblanket andunderdrain (seeTable 5-3).

Do not use wherewater conditions intrench preventproper placementand compaction.

Difficult to achieverequired soilstiffness (seeSec. 6.5.1). Do notuse where waterconditions intrench preventproper placementand compaction.

Foundation Suitable forreplacing over-excavated andunstable trenchbottom as restrictedabove.

Suitable forreplacing over-excavated andunstable trenchbottom asrestricted above.Install andcompact in 12 in.(300 mm)maximum layers.

Suitable forreplacing over-excavated trenchbottom asrestricted above.Install andcompact in 6 in.(150 mm)maximum layers.

Not suitable.

Pipe Zone Embedment

Suitable as restricted above. Workmaterial under pipe to provide uniformhaunch support.

Suitable as restricted above. Difficult toplace and compact in the haunch zone.

Embedment Com-pactionb

Required densitytypically achievedby dumpedplacement.Place and work toensure all excavatedvoids and haunchareas are filled. Usevibratory or impactcompactors.

Minimum density85% standardProctor. Use handtampers, vibratory,or impactcompactors.

Minimum density90% standardProctor. Use handtampers or impactcompactors.Maintain moisturecontent nearoptimum tominimizecompactive effort.

Minimum density95% standardProctor. Use handtampers or impacttampers. Maintainmoisture contentnear optimum tominimizecompactive effort.

aSC5 materials are unsuitable as embedment, but they may be used as final backfill as permitted by the engineer.bMinimum density based on achieving an E ′ of 1,000 psi (6,895 kPa). (See Sec. 6.6.3 and chapter 5.)Reprinted with permission from the Annual Book of ASTM Standards, Copyright ASTM, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.



trench during construction, when water levels are controlled by various pumping orwell-pointing methods, or after construction, when permeable underdrain orembedment materials act as a “french” drain under high groundwater levels. Fieldexperience shows that migration can result in significant loss of pipe support andincreasing deflections that may eventually exceed design limits. The gradation andrelative size of the embedment and adjacent materials must be compatible in order tominimize migration. In general, where significant groundwater flow is anticipated,avoid placing coarse, open-graded materials, such as SC1, above, below, or adjacent tofiner materials, unless methods are employed to impede migration. For example,consider the use of an appropriate soil filter or a geotextile filter fabric along theboundary of the incompatible materials.

The following filter gradation criteria may be used to restrict migration of finesinto the voids of coarser material under a hydraulic gradient.

• D15/d85 < 5 where D15 is the sieve opening size passing 15 percent by weightof the coarser material and d85 is the sieve opening size passing 85 percent byweight of the finer material.

• D50/d50 < 25 where D50 is the sieve opening size passing 50 percent by weightof the coarser material and d50 is the sieve opening size passing 50 percent byweight of the finer material. This criterion need not apply if the coarsermaterial is well graded (see ASTM D2487).

If the finer material is a medium to highly plastic clay (CL or CH), then thefollowing criterion may be used in lieu of the D15/d85 criteria: D15 < 0.02 in. (0.5 mm)where D15 is the sieve opening size passing 15 percent by weight of the coarsermaterial.

The aforementioned criteria may need to be modified if one of the materials isgap graded. Materials selected for use based on filter gradation criteria should behandled and placed in a manner that will minimize segregation.

6.6 TRENCH EXCAVATION ________________________________

6.6.1 ExcavationExcavate trenches to ensure that sides will be stable under all working conditions.Slope trench walls or provide supports in conformance with all local and nationalstandards for safety. Open only enough trench that can be safely maintained byavailable equipment. Place and compact backfill in trenches as soon as practicable,preferably no later than the end of each working day. Excavated material should beplaced away from the trench to minimize the risk of trench wall collapse.

Water control. It is always good practice to remove water from a trenchbefore laying and backfilling pipe. Although circumstances occasionally requirepipe installation in standing or running water conditions, such practice isoutside the scope of this chapter. Prevent runoff and surface water from enteringthe trench at all times.

Groundwater. When groundwater is present in the work area, dewater tomaintain stability of in situ and imported materials. Maintain water level below pipebedding. Use sump pumps, well points, deep wells, geotextiles, perforated under-drains, or stone blankets of sufficient thickness to remove and control water in thetrench. When excavating, ensure the groundwater is below the bottom of cut at alltimes to prevent washout from behind sheeting or sloughing of exposed trench walls.Maintain control of water in the trench before, during, and after pipe installation, anduntil embedment is installed and sufficient backfill has been placed to preventflotation of the pipe (see Sec. 6.7.3). To preclude loss of soil support, employ



dewatering methods that minimize removal of fines and the creation of voids withinin situ materials.

Running water. Control running water that emanates from surface drainageor groundwater to preclude undermining of the trench bottom or walls, thefoundation, or other zones of embedment. Provide dams, cutoffs, or other barriersperiodically along the installation to preclude transport of water along the trenchbottom. Backfill all trenches as soon as practical after the pipe is installed to preventdisturbance of pipe and embedment.

Materials for water control. Use suitably graded materials for foundationlayers to transport running water to sump pits or other drains. Use properly gradedmaterials and/or perforated underdrains to enhance transport of running water, asrequired. Select the gradation of the drainage materials to minimize migration offines from surrounding materials (see Sec. 6.5.2).

Minimum trench width. Where trench walls are stable or supported, providea width sufficient, but no greater than necessary, to ensure working room to properlyand safely place and compact haunching and other embedment materials. The spacebetween the pipe and trench wall must be wider than the compaction equipment usedin the pipe zone. Minimum width at the bottom of the trench should be 1.25 times theoutside diameter of the pipe plus 12 in. (305 mm). In addition to safety considera-tions, the trench width in unsupported, unstable soils will depend on the size andstiffness of the pipe, stiffness of the embedment and in situ soil, and depth of cover.Specially designed equipment may enable the satisfactory installation and embed-ment of pipe in trenches narrower than specified earlier. If the use of such equipmentprovides an installation consistent with the requirements of this manual, minimumtrench widths may be reduced if approved by the engineer.

Support of trench walls. When supports such as trench sheeting, trenchjacks, or trench shields or boxes are used, ensure that support of the pipe embedmentis maintained throughout the installation process. Ensure that sheeting is sufficientlytight to prevent washing out of the trench wall from behind the sheeting. Providetight support of trench walls below viaducts, existing utilities, or other obstructionsthat restrict driving of sheeting.

Supports left in place. Unless otherwise directed by the engineer, sheetingdriven into or below the pipe zone should be left in place to preclude loss of support offoundation and embedment materials. When top of sheeting is to be cut off, make cut1.5 ft (0.5 m) or more above the crown of the pipe. Leave walers and braces in placeas required to support cutoff sheeting and the trench wall in the vicinity of the pipezone. Timber sheeting to be left in place is considered a permanent structural memberand should be treated against biological degradation (e.g., attack by insects or otherbiological forms), as necessary, and against decay if above groundwater. Note thatcertain preservative and protective compounds may pose environmental hazards.Determination of acceptable compounds is outside the scope of this manual.

Movable trench wall supports. Do not disturb the installed pipe or theembedment when using movable trench boxes and shields. Movable supports shouldnot be used below the top of the pipe embedment zone, unless approved methods areused for maintaining the integrity of embedment material. Before moving supports,place and compact embedment to sufficient depths to ensure protection of the pipe. Assupports are moved, finish placing and compacting embedment.

Removal of trench wall support. If the engineer permits the use of sheetingor other trench wall supports that extend into the pipe zone, ensure that neither pipe,foundation, nor embedment materials is disturbed by support removal. Fill voids left



on removal of supports and compact all material to required densities. Pulling thetrench wall support in stages as backfilling progresses is advised.

6.6.2 Trench BottomExcavate trenches to grades directed by the engineer. See Sec. 6.7.1 for guidance oninstalling foundation and bedding.

Excavate trench a minimum of 4 in. (100 mm) below the bottom of the pipe.When ledge, rock, hardpan, or other unyielding material, or cobbles, rubble, debris,boulders, or stones larger than 1.5 in. (40 mm) are encountered in the trench bottom,excavate a minimum depth of 6 in. (150 mm) below the pipe bottom or as directed bythe engineer.

If the trench bottom is unstable or shows a “quick” tendency, overexcavate todepths directed by the engineer.

The native material may be used for bedding and initial backfill if it meets all ofthe criteria of the specified pipe zone embedment materials. The preparation of trenchis discussed in Sec. 6.7.1.

6.7 PIPE INSTALLATION Recommendations for use of the various types of materials classified in Sec. 6.5.1 andTable 5-3 for foundation, bedding, haunching, and backfill are provided in Table 6-2.Installation of pipe in areas where significant settlement may be anticipated, such asin backfill adjacent to building foundations, sanitary landfills, or in other highlyunstable soils, requires special engineering and is outside the scope of this manual.

6.7.1 Preparation of TrenchFoundation and bedding. Install foundation and bedding as required by theengineer according to conditions in the trench bottom. Provide a firm, stable, anduniform bedding for the pipe barrel and any protruding features of its joint (seeFigure 6-2). Provide a minimum of 4 in. (100 mm) of bedding below the barrel and3 in. (75 mm) below any part of the pipe, such as expanded bells, unless otherwisespecified.

Bedding material. In general, the bedding material will need to be animported material to provide the proper gradation and pipe support. It is preferable

Bell Hole(fill after completing pipe joint)

a. Proper bedding support

X Xb. Improper bedding support


Figure 6-2 Examples of bedding support



that the same material is used for the initial backfill. To determine if the nativematerial is acceptable as a bedding material, it should meet all of the requirements ofthe initial backfill. This determination must be made constantly during the pipeinstallation process because native soil conditions vary widely and change suddenlyalong the length of a pipeline.

Rock and unyielding materials. When rock or unyielding material is presentin the trench bottom, install a cushion of bedding, 6 in. (150 mm) minimumthickness, below the bottom of the pipe. Take other steps to protect the pipe ifrequired by the engineer. If there is a sudden transition from rock to a softer materialunder the pipe, steps must be taken to accommodate possible differential settlement.Figure 6-3(b) illustrates one method; however, other methods are also possible.

Unstable trench bottom. Where the trench bottom is overexcavated becauseof unstable or “quick” conditions, install a foundation of SC1 or SC2 material. Use asuitably graded material where conditions may cause migration of fines and loss ofpipe support. Place and compact foundation material in accordance with Table 6-2.For severe conditions, the engineer may require a special foundation, such as piles orsheeting capped with a concrete mat. The use of appropriate geotextiles can controlquick and unstable trench bottom conditions.

Localized loadings. Minimize localized loadings and differential settlementwherever the pipe crosses other utilities or subsurface structures (see Figures 6-3 and6-4) or whenever there are special foundations, such as concrete capped piles orsheeting. Provide a 6 in. (150 mm) minimum cushion of bedding or compacted backfillbetween the pipe and any point of localized loading.

Overexcavation. If the trench bottom is excavated below intended grade, fillthe overexcavation with compatible foundation or bedding material and compact to adensity not less than the minimum densities listed in Table 6-2.

Sloughing. If trench sidewalls slough off during any excavation or installationof pipe zone embedment, remove all sloughed and loose material from the trench.

6.7.2 Placing and Joining PipeLocation and alignment. Place pipe and fittings in the trench with the invertconforming to the required elevations, slopes, and alignment. Provide bell holes inpipe bedding, no larger than necessary, in order to ensure uniform pipe support. Fillall voids under the bell by working in bedding material. In special cases, where thepipe is to be installed to a curved alignment, maintain angular “joint deflection” (axialalignment) and pipe bending radius within acceptable design limits. Pipe should belaid on flat uniform material that is at the appropriate grade. Do not bring pipe tograde by using mounds of soil or other material at discreet points along the length ofthe pipe. When pipe laying is interrupted, secure piping against movement and sealopen ends to prevent the entrance of water, mud, or foreign material.

Jointing. Comply with manufacturer’s recommendations for assembly of jointcomponents, lubrication, and making of joints.

Elastomeric seal (gasketed) joints. Mark, or verify that pipe ends aremarked, to indicate insertion stop position, and that pipe is inserted into pipe orfitting bells to this mark. Push spigot into bell using methods recommended by themanufacturer, keeping pipe true to line and grade. Protect the end of the pipeduring homing and do not use excessive force that may result in overassembledjoints or dislodged gaskets. If full entry is not achieved, disassemble and clean thejoint and reassemble. Use only lubricant supplied or recommended for use by thepipe manufacturer. Do not exceed manufacturer’s recommendations for angular“deflection” (axial alignment).



Adhesive bonded and wrapped joints. When making adhesive bonded andwrapped joints, follow recommendations of the pipe manufacturer. Allow freshly madejoints to set for the recommended time before moving, burying, or otherwisedisturbing the pipe.

6.7.3 Placing and Compacting Pipe Backfill MaterialsPlace embedment materials by methods that will not disturb or damage the pipe.Work in and compact the haunching material in the area between the bedding andthe underside of the pipe before placing and compacting the remainder of the pipezone embedment (see Figure 6-5). Do not permit compaction equipment to contact

Coupling Castin Concrete

SpecialShort Pipe SectionMaximum—Smaller of 2 m or 2 x DMinimum—Smaller of 1 m or 1 x D

max.25 mm

Fill below pipe to structure baseshould be same as pipe zone material (Typ.)

maximum 25

a. Connection to rigid structures

Flexible JointLocated at

Drop-off point

Coupling FlexibleJoint (Typ.)

Standard Pipe Section

Make-UpSection

Short Pipe

Standard Pipe

Short Section LengthMaximum—Smaller of 2 m or 2 3 DMinimum—Smaller of 1 m or 1 3 D

BedFoundation (if required)

Native SoilDrop-Off

PointRock

b. Change in foundation soil stiffness


Figure 6-3 Accommodating differential settlement



and damage the pipe. Use compaction equipment and techniques that are compatiblewith materials used and located in the trench.

Compaction of soils containing few fines (SC1 and SC2 with less than5 percent fines). If compaction is required, use surface plate vibrators, vibratoryrollers, or internal vibrators. The compacted lift thickness should not exceed 12 in.(300 mm) when compacted with surface plate vibrators or vibratory rollers; whencompacted with internal vibrators, it should not exceed the length of the internalvibrators. Density determination should typically be in accordance with ASTM D4253and D4254 (relative density). In some cases, the density of SW or SP soils may bedetermined by ASTM D698 (standard Proctor) if the test results in a clearly definedcompaction curve.

Compaction of soils containing some fines (SC2 with 5 to 12 percentfines). These soils may behave as a soil containing few fines or as a soil containing asignificant amount of fines. The methods of compaction and density determinationshould be based on the method that results in the higher in-place density.

C

r1

r1

f

r2

Bed

C ≥r1 + r2

2

f ≥ r1 + r2

2

But not less than 100 mmor sufficient room toplace and compact backfill

a. Spacing between pipes in the same trench

r2

> 70 RDfGravel

or90 SPDSandBed

But notless than 150 mm

b. Cross over


Figure 6-4 Adjacent piping systems

Using board orother deviceto push and compactembedmentmaterial underpipe.

Pipe First lift ofembedment

First lift ofembedmentPipe

W RO N G !

a. Ensuring firm pipe support b. Improper haunch

Bedding Bedding Correct: Pipe firmly supported Wrong: Poor pipe support


Figure 6-5 Proper compaction under haunches



Compaction of soils containing a significant amount of fines (SC3, SC4,and SC5 [CH and MH]). These soils should be compacted with impact tampers orwith sheepsfoot rollers. Density determination should be in accordance with ASTMD698 (standard Proctor). The maximum density occurs at the optimum moisturecontent. Less effort is required to reach a given density when the moisture content iswithin 2 percentage points of the optimum moisture. A rapid method of determiningthe percent compaction and moisture variation is described in ASTM D5080. Forcompaction levels of 90 percent standard Proctor or higher, the compacted liftthickness should not exceed 6 in. (150 mm).

Determination of the in-place density of soils. The in-place density of anyin situ or fill soil may be determined in accordance with ASTM D1556, D2167, D2922,D4564, D4914, or D5030. The applicable test method will depend on the type of soil,moisture content of the soil, and the maximum particle size present in the soil. Themoisture content of the soil may be determined in accordance with ASTM D2216,D3017, D4643, D4944, or D4959. When using nuclear density-moisture gages (ASTMD2922 and D3017), the gauge should be site-calibrated in the proximity of the pipeand in the excavation unless otherwise indicated by the gauge manufacturer.

Minimum density. The minimum embedment density should be establishedby the engineer based on an evaluation of specific project conditions. Higher or lowerdensities than those recommended in Table 6-2 may be appropriate. Minimumdensities given in Table 6-2 are based on attaining an average modulus of soilreaction E′ of 1,000 psi (6.9 MPa) and are intended to provide satisfactory embedmentstiffness in most installation conditions. (See chapter 5 for the significance of E′.)

Consolidation using water. Consolidation of pipe zone embedment usingwater (jetting or saturation with vibration) should be done only under controlledconditions and when directed by the engineer.

Minimum cover. To preclude damage to the pipe and disturbance to pipeembedment, a minimum depth of backfill above the pipe should be maintained beforeallowing vehicles or heavy construction equipment to traverse the pipe trench. Theminimum depth of cover should be established by the engineer based on anevaluation of specific project conditions, such as pipe diameter and stiffness, soil typeand stiffness, and live load type and magnitude. In the absence of an engineeringevaluation, the following minimum cover requirements should be used.

For embedment materials installed to the minimum densities given in Table 6-2and live loads similar to AASHTO H-20, provide cover (i.e., depth of backfill above topof pipe) of at least 24 in. (0.6 m) for SC1 embedment; a cover of at least 36 in. (0.9 m)for SC2, SC3, or SC4 embedment, before allowing vehicles or construction equipmentto traffic the trench surface; and at least 48 in. (1.2 m) of cover before using ahydrohammer for compaction unless approved by the engineer. Where constructionloads may be excessive (e.g., cranes, earth-moving equipment, or other vehicles wherewheel loads exceed the AASHTO H-20 loading) minimum cover should be increased asdetermined by the engineer, or special structures, such as relief slabs at grade, maybe installed to reduce the load transferred to the pipe.

If there is a risk of pipe flotation, then the minimum cover should be one pipediameter. If a specific analysis is made of the buoyant force of an empty pipecompared to the submerged weight of soil over the pipe, this minimum cover may bereduced.



6.7.4 Connections and Appurtenant StructuresConnections to manholes and rigid structures and changing foundationsoils. When differential settlement can be expected, such as at the ends of casingpipe, when the pipe enters a manhole, at anchor blocks, or where foundation soilschange stiffness, provide a flexible system capable of accommodating the anticipatedsettlement. This may be accomplished by placing a joint as close as practicallypossible to the face of the structure and a second joint within one to two pipediameters of the face of the structure (see Figure 6-3). Alternatively attach the pipe tothe rigid structure with a flexible boot capable of accommodating the anticipateddifferential movement. Other methods of accommodating differential settlements areavailable.

Vertical risers. Provide support for vertical risers as commonly found atservice connections, cleanouts, and drop manholes to preclude vertical or lateralmovement. Prevent the direct transfer of thrust due to surface loads and settlement,and ensure adequate support at points of connection to main lines.

Exposing pipe for making service line connections. When excavating for aservice line connection, excavate material from above the top of the existing pipebefore removing material from the sides of the pipe. When backfilling excavations ofexisting lines, the materials and construction methods used should restore theinstallation to its condition prior to excavation.

Pipe caps and plugs. Secure caps and plugs to the pipe to prevent movementand resulting leakage under test and service pressures. If lines are to be tested underpressure, any plugs and caps must be designed to safely carry the test pressure.

Adjacent piping systems. Space parallel piping systems laid within acommon trench sufficiently far apart to allow compaction equipment to compact thesoil between the pipes. The minimum distance that should be allowed between pipesis the average of the radii of the two adjacent pipes, but not less than 4 in. (100 mm);see Figure 6-4(a). When mechanical compaction equipment is used, a clearance of6 in. (150 mm) greater than the width of the widest piece of equipment may beconsidered as a practical clearance between the pipes. Compact the soil between thepipes in the same manner as the soil between the pipe and the trench wall, takingspecial care to compact the soil in the haunch zone of each pipe.

When one piping system will cross over another, the minimum vertical clearspace between the two pipes should be the average of the radii of the two pipes butnot less than 12 in. (300 mm); see Figure 6-4(b). The trench in which the lower pipeis installed should be backfilled with SC1 or SC2 material compacted to a minimumof 90 percent of standard Proctor density, or 70 percent relative density.

6.7.5 Thrust BlocksInstallation requirements related to thrust blocks are discussed in chapter 7.

6.8 FIELD MONITORING _________________________________Compliance with installation requirements for trench depth, grade, water conditions,foundation, embedment and backfill materials, joints, density of materials in place,and safety should be monitored according to the contract documents. Leakage testingspecifications are not within the scope of this manual.

Deflection. Monitor the deflection level in the pipe throughout the installationprocess for conformance to the requirements of the contract specifications and themanufacturer’s recommendations. Conduct deflection measurement programs early



in a project to verify that the construction procedures being used are adequate. Theallowable deflection at the time of installation is the long-term allowable deflectionreduced by the effects of deflection lag. If necessary, also consider the effects ofvertical ovalling during compaction.

6.9 CONTRACT DOCUMENT RECOMMENDATIONS _________The following guidelines may be included in contract documents for a specific projectto cover installation requirements. ASTM D3839 provides similar guidelines and iswritten in a specification-type format. In either case, applications for a particularproject may require that the engineer provide more specific requirements in severalareas, including:

• Maximum particle size if different from Sec. 6.5.2.• Restrictions on use of categories of embedment and backfill materials.• Specific gradations of embedment materials for resistance to migration.• State-specific restrictions on leaving trenches open.• Restrictions on mode of dewatering and design of underdrains.• Requirements on minimum trench width.• Restrictions or details for support of trench walls.• Specific bedding and foundation requirements.• Specific restrictions on methods of compaction.• Minimum embedment density if different from these recommendations;

specific density requirements for backfill (e.g., for pavement subgrade).• Minimum cover requirements.• Detailed requirements for support of vertical risers, standpipes, and stacks to

accommodate anticipated relative movements between pipe and appurte-nances. Detailing to accommodate thermal movements, particularly at risers.

• Detailed requirements for manhole connections.• Requirements on methods of testing compaction and leakage.• Requirements on deflection and deflection measurements, including method

and time of testing.

REFERENCES _____________________________________________AASHTO H-20. Washington, D.C.: Ameri-

can Association of State Highway andTransportation Officials.

Standard Classification of Soils for Engi-neering Purposes (Unified Soil Classi-fication System). 1993. ASTM D2487.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard for Fiberglass Pressure Pipe. 1995.ANSI/AWWA C950. Denver, Colo.:American Water Works Association.

Standard Guide to Site Characterization forEngineering, Design, and Construc-tion Purposes. 1993. ASTM D420.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard Practice for Description and Iden-tification of Soils (Visual–Manual Pro-cedure). 1993. ASTM D2488. WestConshohocken, Pa.: American Societyfor Testing and Materials.

Standard Practice for Underground Instal-lation of ‘Fiberglass’ (Glass-Fiber-Re-inforced Thermosetting-Resin) Pipe.1994. ASTM 3839. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Practice for Underground Instal-lation of Thermoplastic Pipe for Sewersand Other Gravity-Flow Applications.1989. ASTM D2321. West Consho-hocken, Pa.: American Society for Test-ing and Materials.



Standard Terminology Relating to Materialsfor Roads and Pavements. 1994. ASTMD8. West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard Terminology Relating to PlasticPiping Systems. 1994. ASTM F412.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard Terminology Relating to Plastics.1993. ASTM D883. West Consho-hocken, Pa.: American Society forTesting and Materials.

Standard Terminology Relating to Soil, Rock,and Contained Fluids. 1990. ASTMD653. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Method for Density and UnitWeight of Soil in Place by the RubberBalloon Method. 1994. ASTM D2167.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard Test Method for Density and UnitWeight of Soil in Place by the Sand-Cone Method. 1990. ASTM D1556.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.

Standard Test Method for Density of Soil andRock in Place by the Water Replace-ment Method in a Test Pit. 1989. ASTMD5030. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Method for Density of Soil inPlace by the Sleeve Method. 1993.ASTM D4564. West Conshohocken,Pa.: American Society for Testing andMaterials.


Standard Test Method for Determination ofWater (Moisture) Content of Soil by Di-rect Heating Method. 1989. ASTMD4959. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Method for Determination ofWater (Moisture) Content of Soil bythe Microwave Oven Method. 1993.ASTM D4643. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Test Method for Field Determina-tion of Water (Moisture) Content of Soilby the Calcium Carbide Gas PressureTester Method. 1989. ASTM D4944.West Conshohocken, Pa.: American So-ciety for Testing and Materials.

Standard Test Method for Laboratory Deter-mination of Water (Moisture) Contentof Soil and Rock. 1992. ASTM D2216.West Conshohocken, Pa.: American So-ciety for Testing and Materials.

Standard Test Method for Liquid Limit,Plastic Limit, and Plasticity Index ofSoils. 1995. ASTM D4318. West Con-shohocken, Pa.: American Society forTesting and Materials.

Standard Test Method for Minimum IndexDensity and Unit Weight of Soils andCalculation of Relative Density. 1991.ASTM D4254. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Test Method for Rapid Determi-nation of Percent Compaction. 1993.ASTM D5080. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Test Method for Water Content ofSoil and Rock in Place by NuclearMethods (Shallow Depth). 1988. ASTM3017. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Methods for Density of Soiland Rock in Place by the Sand Re-placement Method in a Test Pit. 1989.ASTM D4914. West Conshohocken,Pa.: American Society for Testing andMaterials.

Standard Test Methods for Density of Soiland Soil-Aggregate in Place by NuclearMethods (Shallow Depth). 1991. ASTM2922. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Methods for Maximum IndexDensity and Unit Weight of Soils andCalculation of Relative Density. 1993.ASTM D4253. West Conshohocken,Pa.: American Society for Testing andMaterials.



Test Method for Laboratory CompactionCharacteristics of Soil Using ModifiedEffort [56,000 ft-lbf/ft (2,700 kN-m/m)].1991. ASTM D1557. West Consho-hocken, Pa.: American Society forTesting and Materials.

Test Method for Laboratory CompactionCharacteristics of Soil Using StandardEffort [12,400 ft-lbf/ft3 (600 kN-m/m3)].1991. ASTM D698. West Consho-hocken, Pa.: American Society forTesting and Materials.



Buried Pipe Thrust Restraints

BURIED PIPE THRU ST RESTRAINTS

7.1 UNBALANCED THRUST FORCES ________________________Unbalanced thrust forces occur in pressure pipelines at changes in direction (i.e.,elbows, wyes, tees, etc.), at changes in cross-sectional area (i.e., reducers), or atpipeline terminations (i.e., bulkheads). These forces, if not adequately restrained, maycause pipeline movement resulting in separated joints and/or pipe damage. Thrustforces are: (1) hydrostatic thrust due to internal pressure of the pipeline, and (2)hydrodynamic thrust due to changing momentum of flowing fluid. Since mostpressure lines operate at relatively low velocities, the hydrodynamic force is verysmall and is usually ignored.

7.1.1 Hydrostatic ThrustTypical examples of hydrostatic thrust are shown in Figure 7-1. The thrust in deadends, tees, laterals, and reducers is a function of internal pressure P andcross-sectional area A at the pipe joint. The resultant thrust at a bend is also afunction of the deflection angle ∆ and is given by:

T = 2PA sin (∆/2) (7-1)

Where:

T = hydrostatic thrust, lb

P = internal pressure, psi

AWWA MANUAL M45

Chapter 7

91


A = (π/4) Dj2 = cross-sectional area of pipe joint, in.,

where Dj is the pipe joint diameter, in.

∆ = deflection angle of bend, degrees

7.2 THRUST RESISTANCE For buried pipelines, unbalanced horizontal thrust forces have two inherent sourcesof resistance: (1) frictional drag from dead weight of the pipe, earth cover, andcontained fluid, and (2) passive resistance of soil against the pipe or fitting in thedirection of the thrust. If this resistance is not sufficient to resist the thrust, then itmust be supplemented by increasing the supporting area on the bearing side of thefitting with a thrust block; increasing the frictional drag of the line by “tying”adjacent pipe to the fitting; or otherwise anchoring the fitting to limit or preventmovement. Unbalanced uplift thrust at a vertical deflection is resisted by the deadweight of the fitting, earth cover, and contained fluid. If this type of resistance is notsufficient to resist the thrust, then it must be supplemented by increasing the deadweight with a gravity-type thrust block; increasing the dead weight of the line by“tying” adjacent pipe to the fitting; or otherwise anchoring the fitting to limit orprevent movement.

D

∆2

∆2

∆2

∆

∆

∆

2

∆2

∆2

PAPA sin

PA

PA1

PA0

T = PA0

PA2

PA2

PA

PA

PA0

PA1

T = PA

T = PA0

PA2

Bend

T = 2PA sin

Dead End

Tee Reducer

T

T = P(A1 – A2)

T = 2PA2 cos – PA1

T

Wye

Bifurcation

Figure 7-1 Thrust force definitions



7.3 THRUST BLOCKS Concrete thrust blocks increase the ability of fittings to resist movement byincreasing the bearing area and the dead weight of the fitting. Typical thrust blockingof a horizontal bend (elbow) is shown in Figure 7-2.

Calculation of size. Ignoring the dead weight of the thrust block, the blocksize can be calculated based on the bearing capacity of the soil:

Area of block = LB × HB = (T × FS)/σ (7-2)

Where:

LB × HB = area of bearing surface o f thrust block, ft2

T = thrust force, lb

σ = bearing valuefor soil, lb/ft2

FS = design factor, 1.5

Typical values for conservative horizontal bearing strengths of various soil typesare listed in Table 7-1.

...

.. .

. ...

.

. . ..

.

. ..

.

. ...

..

.

.

... ...

..

. ....

.

.

... ..

....

.

... .

.

.. ..

.

... ..

.

.

.

.

...

.

.

.

.. .

.

LB

A

A

HB

HB

h

Piles

h

ReinforcingSteel

Section A–A

Alternate Section A–A Alternate Section A–A

Figure 7-2 Typical thrust blocking of a horizontal bend

BURIED PIPE THRUST RESTRAINTS 93


If it is impractical to design the block for the thrust force to pass through thegeometric center of the soil bearing area, then the design should be evaluated forstability.

After calculating the concrete thrust block size, and reinforcement if necessary,based on the bearing capacity of soil, the shear resistance of the passive soil wedgebehind the thrust block should be checked because it may govern the design. For athrust block having its height, HB, less than one-half the distance from the groundsurface to base of block, h, the design of the block is generally governed by the bearingcapacity of the soil. However, if the height of the block, HB, exceeds one-half h, thenthe design of the block is generally governed by shear resistance of the soil wedgebehind the thrust block. Determining the value of the bearing and shear resistance ofthe soil and thrust block reinforcement is beyond the scope of this manual. Consultinga qualified geotechnical professional is recommended.

Typical configurations. Determining the bearing value, σ, is the key to “sizing”a thrust block. Values can vary from less than 1,000 lb/ft2 (48 kN/m2) for very softsoils to several tons per square foot (kN/m2) for solid rock. Knowledge of local soilconditions is necessary for proper sizing of thrust blocks. Figure 7-2 shows severaldetails for distributing thrust at a horizontal bend. Section A–A is the more commondetail, but the other methods shown in the alternate sections may be necessary inweaker soils. Figure 7-3 illustrates typical thrust blocking of vertical bends. Design ofthe block for a bottom bend is the same as for horizontal bend, but the block for a topbend must be sized to adequately resist the vertical component of thrust with deadweight of the block, bend, water in the bend, and overburden.

Proper construction is essential. Most thrust block failures can be attributed toimproper construction. Even a correctly sized block can fail if it is not properlyconstructed. A block must be placed against undisturbed soil and the face of the blockmust be perpendicular to the direction of and centered on the line of action of thethrust. A surprising number of thrust blocks fail because of inadequate design orimproper construction. Many people involved in construction and design do notrealize the magnitude of the thrusts involved. As an example, a thrust block behind a36 in. (900 mm), 90 degree bend operating at 100 psi (689 kPa) must resist a thrustforce in excess of 150,000 lb (667 kN). Another factor frequently overlooked is thatthrust increases in proportion to the square of pipe diameter. A 36 in. (900 mm) pipeproduces approximately four times the thrust produced by an 18 in. (450 mm) pipeoperating at the same internal pressure.

Table 7-1 Horizontal soil-bearing strengths

Soil Bearing Strength σ (lb/ft2)*

Muck 0Soft clay 1,000Silt 1,500Sandy silt 3,000Sand 4,000Sandy clay 6,000Hard clay 9,000

*Although the bearing strength values have been used successfully in the design of thrust blocks and are considered to beconservative, their accuracy is dependent on accurate soil identification and evaluation. The design engineer must select theproper bearing strength of a particular soil type.



Adjacent excavation. Even a properly designed and constructed thrust blockcan fail if the soil behind the block is disturbed. Properly sized thrust blocks havebeen poured against undisturbed soil only to fail because another utility or anexcavation immediately behind the block collapsed when the line was pressurized. If the riskof future nearby excavation is high, the use of restrained (tied) joints may be appropriate.

7.4 JOINTS WITH SMALL DEFLECTIONS The thrust at pipe joints installed with angular deflection is usually so small thatsupplemental restraint is not required.

Small horizontal deflections. Thrust T at horizontal deflected joints isresisted by friction on the top and bottom of the pipe as shown in Figure 7-4.Additional restraint is not required when:

T ≤ fLp (Wp + Ww + 2We) (7-3)

Where:

T = 2PA sin (θ /2) = result and thrust force, lb where θ is the deflection angle created by the deflected joint, degrees

f = coefficient of friction

Lp = length of pipe, ft

Wp = weight of pipe, lb/lin ft

..

...

...

.

.. ..

.

...

.

...

. ..

Finished Grade

Concrete Collar

Figure 7-3 Typical profile of vertical bend thrust blocking



Ww = weight of fluid in pipe, lb/lin ft

We = earth cover load, lb/lin ft

The passive soil resistance of the trench backfill against the pipe is ignored inthe previous analysis. Depending on the installation and field conditions, the passivesoil resistance of the backfill may be included to resist thrust.

The selection of a value for the coefficient of friction f is dependent upon the typeof soil and the roughness of pipe exterior. Design values for the coefficient of frictiongenerally vary from 0.25 to 0.50.

Determination of earth cover load should be based on a backfill density andheight of cover consistent with what can be expected when the line is pressurized.Values of soil density vary from 90 lb/ft3 to 130 lb/ft3 (14 kN/m3 to 20 kN/m3),depending on the degree of capaction. We may be conservatively determined using theMarston equation for loads imparted to a flexible pipe, as follows:

We = (Cd) (W) (Bd) (Bc) (7-4)

Where:

We = earth load, lb/lin ft

Cd = a coefficient based on type of backfill soil and on the ratio of H (depth of fill to top if pipe, ft) Bd (see Figure 7-5)

T TT = 2PA sin

2

LpLp

Lp

Lp

f Lp

2Lp

F=T

A

A

Ww

Wp

We

We

T

Section A–A

f Lp (Wp + Ww + We )

F

Plan View

2θ

θθ

θ

Figure 7-4 Restraint of thrust at def lected joints on long-radius horizontal curves



A = Cd K µ and K µ' = 0.1924 for granular materials without cohesionB = Cd K µ and K µ' = 0.165 maximum for sand and gravelC = Cd K µ and K µ' = 0.150 maximum for saturated topsoilD = Cd K µ and K µ' = 0.130 ordinary maximum for clayE = Cd K µ and K µ' = 0.110 maximum for saturated clay

Computation Diagram for EarthLoads on Trench Conduits(conduits buried in trenches)

0.1 0.15 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.5

Values of H/Bd

0.1

0.15

0.2

0.25

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.5C

oeffi

cien

t Cd

Coe

ffici

ent C

d

Expanded Scale of Computation Diagramfor Earth Loads on Trench Conduits

1 1.5 2 3 4 5 6 7 8 9 10 15 20 25 30 40

Values of H/Bd

A

BC

D

E

1

1.5

2

3

4

5

EDCBA

Figure 7-5 Computation diagram for earth loads on trench conduits



W = unit weight of soil, lb/ft3

Bd = ditch width at top of pipe, ft

Bc = outside diameter of pipe, ft

Small vertical deflections with joints free to rotate. Uplift thrust atdeflected joints on long-radius vertical curves is resisted by the combined deadweight, Wt, as shown in Figure 7-6. Additional restraint is not required when:

T ≤ Lp (Wp + Ww + We) COS (ϕ – θ/2) (7-5)

Where:

T = 2PA sin (θ/2)

Lp = length of standard or beveled pipe, ft

T

T

T = 2PA sin 2

2

θ

θ

θ

θ

θ

2

Lp

LpLp

Lp

2

Lp

ϕϕ

A

A

Ww

Wp

We

Section A–A

Wt = (Wp + Ww + We )

F = THorizontal Plane

( – )

Profile View

Figure 7-6 Restraint of uplift thrust at deflected joints on long-radius vertical curves




Ww = weight of water in pipe, lb/lin ft

We = earth cover load, lb/lin ft

ϕ = slope angle, degrees = slope angle, degrees

θ = deflection angle, degrees, created by angular deflection of joint

7.5 RESTRAINED (TIED) JOINTS ____________________________Unbalanced thrust forces at fittings or deflected joints may be resisted by usingrestrained joint(s) across the deflected joint or by tying adjacent pipes to the fitting.This method fastens a number of pipe on each side of the fitting to increase thefrictional drag of the connected pipe to resist the fitting thrust. Since thrustdiminishes from a maximum value at a fitting to zero at distance L from the fitting,requirements for longitudinal strength to resist thrust can be calculated for the pipelength immediately adjacent to the fitting and prorated on a straight line basis for theremainder of the pipe within the tied distance L. Frictional resistance on the tied pipeacts in the opposite direction of resultant thrust T. Section A–A in Figure 7-4 shows adiagram of the external vertical forces acting on a buried pipe with horizontal thrustand the corresponding frictional resistance. Uplift thrust restraint provided bygravity-type thrust blocks, shown for the top bend in Figure 7-3, may also be providedby the alternate method of increasing the dead weight of the line by tying adjacentpipe to the vertical bend. Section A–A in Figure 7-6 shows a diagram of the verticalforces acting on a buried vertical (uplift) bend used in determining the thrustresistance by dead weight.

T = 2PA sin ∆2

__

L

Joint Not Tied

F = 2Lf(Wp+Ww+2 We) = T

L∆

Figure 7-7 Thrust restraint with tied joints at bends



As previously stated, both of these analyses ignore the passive soil resistance ofthe backfill against the pipe. Depending on the installation and field conditions, thepassive soil resistance of the backfill may be included to resist thrust.

Horizontal bends and bulkheads. As illustrated in Figure 7-7, the frictionalresistance F needed along each leg of a horizontal bend is PA sin (∆/2). Frictionalresistance per lin ft of pipe against soil is equal to:

Frictional resistance/ft of pipe = f (2We + Wp + Ww) (7-6)

Where:f = coefficient of friction between pipe and soil

We = overburden load, lb/lin ft


Ww = weight of water in pipe, lb/lin ft

F = frictional resistance

Therefore, the length of pipe L to be tied to each leg of a bend is calculated as:

L = PA sin (∆/2)

f (2We + Wp + Ww)(7-7)

Where:

L = length of pipe tied to each bend leg, ft


A = cross -sectional area, in.2

∆ = deflection angle of bend, degrees

f = coefficient of friction between pipe and soil




The length of pipe to be tied to a bulkhead or tee leg is:

L = PA

f (2We + Wp + Ww)(7-8)

Where:

L = length of pipe tied to bulkhead to tee leg, ft with all other variables as defined previously.



Vertical (uplift) bends. As illustrated in Figure 7-8, the dead weight resis-tance needed along each leg of a vertical bend is 2PA sin (∆/2). Dead weight resistanceper lin ft of pipe in a direction opposite to thrust is:

Dead weight resistance/ft of pipe = (We + Wp + Ww) COS (ϕ–∆/2) (7-9)

Where:




ϕ = slope angle, degrees (see Figure 7-8)

∆ = deflection angle of bend, degrees (see Figure 7-8)

Length of pipe L to be tied to leg of a vertical (uplift) bend is calculated as:

L = PA [ sin (∆/2) ]

(We + Wp + Ww) COS [ ϕ − (∆/2) ](7-10)

with variables as defined previously.

L1 = PA sin ∆/2

(We + Wp + Ww) COS ( ϕ1 − ∆/2) (7-11)

L1 L2

T = 2PA sin ∆

∆

2

Horizontal Plane

ϕ ϕ1 2

PA

PA

Figure 7-8 Length of tied pipe on each leg of vertical (uplift) bend



L2 = PA sin ∆/2

(We + Wp + Ww) COS (ϕ2 − ∆/2)(7-12)

Vertical downward bends are resisted by bearing of the trench against thebottom of the pipe. Properly bedded pipe should not have to be investigated for thiscondition.

Transmission of thrust force through pipe. In addition to calculating pipelength to be tied to a fitting, designers must be sure that tied pipe lengths havesufficient strength in the longitudinal direction to transmit thrust forces. Themaximum thrust force for which the pipe adjacent to a bend must be designed isequal to:

Fy =

5.43∆ + 0.063 ∆2

1,000 PA for 0 < ∆ ≤ 90° (7-13)

Fy = PA for ∆ > 90° (7-14)

Where:

Fy = maximum axial thrust force for which the pipe adjacent a bend must be

designed, lb



∆ = bend deflection angle, degrees



Aboveground Pipe Design and Installation

ABOVEGROUN D PIPE DESIGN AND IN STALLATION

8.1 INTRODUCTION ______________________________________This chapter addresses the design and installation of fiberglass pipeline systems inaboveground applications for sizes 16 in. (400 mm) and smaller, and only for pipelines that have restrained joints. Different design provisions and supporting methodsmay be applicable for specific project requirements, larger diameters, or a particularpiping product. Consult with the manufacturer and the piping engineer forappropriate design considerations.

8.2 TEST METHODS AND PHYSICAL PROPERTIES ___________The ultimate and allowable design stresses and physical properties for abovegroundfiberglass pipe are based on standardized test methods; these properties are based onthe minimum reinforced wall thickness. Table 8-1 provides a list of various AmericanSociety for Testing and Materials (ASTM) standardized test methods and the type ofdata the tests provide. The comments column provides information on safety factorsfor design stresses. Most manufacturers provide data obtained at both 75°F (24°C)and at the maximum allowable working temperature of the pipe. Some manufactur-ers take exception to various aspects of ASTM test methods and use modifiedtechniques. Prior agreement relative to modified test methods is essential.

AWWA MANUAL M45

Chapter 8

103


Table 8-1 Standard test methods and design properties

Property Test Comments

Axial tensile ASTM D2105 Ultimate stress or ASTM D2105 Design stress ASTM D638 Commonly = 25% ultimate Modulus of elasticity Usually <2 × 106 psi (13.8 × 103 MPa)

Axial compression ASTM D695 Ultimate stress Design stress Commonly = 25% ultimate Modulus of elasticity Usually <2 × 106 psi (13.8 × 103 MPa)

Short-term failure pressure ASTM D1599 From test results Ultimate hoop tensile stress

Hydrostatic design stress ASTM D2992 Procedure A cyclic pressure Cyclic pressure rating for 657 × 106

cyclesService factor = 1.0

Procedure B static pressure Static pressure rating for 438,000 hService factor = 0.56

Coefficient of linear thermal expansion ASTM D696 *

Collapse rating Ultimate pressure ASTM D2924 Design pressure Allowable design: 33% to 75% of ultimate

External loading ASTM D2412 Stiffness factor At 5% deflection Pipe stiffness At 5% deflection Hoop flexural modulus Calculated from stiffness factor at

5% deflection

Beam bending † ‡

Ultimate stress From test results Design stress Allowable = 12.5% of ultimate Modulus of elasticity ASTM D2925 From long-term tests

Thermal conductivity Values typically range from 0.87 to2.9

*ASTM D696 may not always produce appropriate data. Some manufacturers modify this test method to accuratelydetermine the thermal expansion coefficient.†Ultimate beam bending stress typically comes from testing a simply supported (two typical supports) pipe with aconcentrated load at the center. The recommended 8:1 safety factor accounts for typical operation with combinations ofbending and internal pressure. This combination could shorten the service life if not considered.‡There is no universally accepted method for establishing thermal conductivity to fiberglass pipe. The usual techniqueconsists of applying heat at a controlled rate to the pipe inside diameter in a water bath. Temperature drops across the pipewall then gives thermal conductivity as Btu/(ft2)(h)(°F)/in. (W/m-K).



8.3 INTERNAL PRESSURE RATING _________________________The hydrostatic design basis for internal pressure rating of fiberglass piping is basedon a long-term test performed in accordance with ASTM D2992. This standardmethod presents two ways to establish the pressure rating. Procedure A determinesthe hydrostatic design basis for cyclic conditions; procedure B establishes the ratingfor static pressure applications. Figures 8-1 and 8-2 illustrate typical behavior offiberglass pipe tested by procedure A and procedure B.

The method involves performing tests on a minimum of 18 specimens loaded tovarious stress levels at constant temperature and with no axial constraints. Thestress levels are designed to produce failures in both the short and long terms(>10,000 h). Data plotted as hoop stress versus time or cycles yield a regression curve.The curve is extrapolated one-and-a-half decades.

The hydrostatic design basis is the hoop stress (or strain) that provides anestimated life at 50 years (static) or 657 million cycles (cyclic) for American WaterWorks Association (AWWA) applications. The allowable design stress results fromapplying service design factors (FS) to the extrapolated values. Service factors willvary from application to application. A number of code bodies have adopted a servicedesign factor of 0.8 to 1.0 for the cyclic conditions (procedure A) and 0.50 to 0.56 forthe static conditions (procedure B).

In ANSI/AWWA Standard C950, the design factors (FS) are the reciprocal of theservice design factors and are always ≥1.

A range of piping constructions and materials are available in the market. Theconsumer will benefit by applying the rationale described in this chapter to thehydrostatic design basis stress or strain provided by the manufacturer.

Filament Wound EpoxyPipe Tested per ASTM D2992Proc. A

103 104 105 106 107 108 109

Number of Cycles

1

3

6

9

1215

30

60

Hoo

p Te

nsile

Str

ess

1,00

0 ps

i

NOTE: This is representative data. Consult the manufacturer for specific product rating.


Figure 8-1 Fatigue resistance (cyclic internal pressure)

ABOVEGROUND PIPE DESIGN AND INSTALLATION 105


8.3.1 Hoop Tensile Stress CalculationsThe equation for calculating the hoop stress is as follows:

S =

P (D − t)2t

(8-1)

Where:

S = design hoop stress, psi

D = average reinforced OD, in.

P = internal pressure, psig

t = minimum reinforced wall thickness, in.

8.3.2 Hoop Strain CalculationsThe equation for calculating hoop strain is as follows:

ε = SET

(8-2)

Where:

ε = hoop strain, in./in.

ET = hoop tensile modulus of elasticity, psi

Filament wound epoxy pipe tested per ASTM D2992Proc. B

10 102 103 104 105 106

Time, h

1

3

6

9

1215

30

60

Hoo

p Te

nsile

Str

ess

1,00

0 ps

i

Figure 8-2 Fatigue resistance (static internal pressure)



8.4 THERMAL EXPANSION AND CONTRACTION ___________Fiberglass pipe may have a different expansion rate in the hoop and axial directions.For example, a filament wound pipe with a 55° winding angle has about the samethermal expansion as steel in the hoop direction. In the axial direction, it is abouttwice the expansion as that of steel. The total expansion or contraction for a pipesystem is determined by the following equation:

Lc = (12) (Ct) (L) (Tc) (8-3)

Where:

Lc = length change, in.

Ct = coefficient of thermal expansion axial in./in./°F

L = length of line between anchors, ft

Tc = temperature change, °F (Maximum operating temperature minus installation temperature for expansion. Installation temperature minus minimum operating temperature for contraction.)

Example 8-1: Find the change in length per lin ft of line for a 2-in. nominalpipeline with a temperature change of 60°F and coefficient of expansion of 1.09 × 10–5.

Lc = (12) (1.09 × 10−5) (1) (60) = 0.0078 in./ft (8-4)

To determine the effects of thermal expansion and contraction on a pipingsystem, it is important to know the:

• design temperature conditions• size and physical properties of the pipe• layout of the system, including dimensions and the thermal movement, if any,

of the terminal points• limitations on end reactions

8.5 THERMAL EXPANSION DESIGN _______________________In the design of aboveground pipelines, the supports and guides for the pipe becomeimportant considerations because of thermal expansion.

In addition to pressure resistance and life limitations, the effects of thermalexpansion and contraction should be considered. A number of methods accommodatethe length changes associated with thermal expansion and contraction. The four mostcommonly used methods include:

• anchoring and guiding• direction changes• expansion loops• mechanical expansion jointsGuides, expansion loops, and mechanical expansion joints are installed in

straight lines that are anchored at each end. Experience has shown that directionchanges are the least expensive method of accommodating thermal expansion. Guide



spacing is the next most economical method, followed by mechanical expansion jointsand expansion loops.

For small temperature changes and piping systems that consist of short runlengths, it is usually unnecessary to make special provisions for thermal expansion.However, any system should have the capability of accommoding length changes. Themethodology provided in Sec. 8.7 solves this design criterion.

Experience has shown that aboveground piping systems need anchors atapproximately 300 ft (91 m) intervals. (NOTE: This value may vary for larger pipesizes.) These anchors limit pipe movement caused by vibrations and transient loadingconditions. Anchors should fasten all transition points within the system. Transitionpoints are places where pipe diameter, material, elevation or direction changes, ormanufacturer changes. Anchors at transition points limit the transfer of thermal endloads from line section to line section.

8.5.1 Thermal End LoadsThe axial modulus of elasticity of fiberglass pipe can vary from approximately1.5 percent to 10 percent of steel. This relatively low modulus is an advantage thatbecomes apparent during the design phase. The low modulus results in lower endloads requiring restraining equipment less strong than that used for metallic pipe-lines. Internal pressures in the piping system can result in some length change.Experience has shown that this elongation is often insignificant and may not need tobe considered in the design.

The equation for calculating the thermal end load is:

EL = (Ct) (E) (A) (Tc) (8-5)

Where:

EL = thermal end load, lb

Ct = coefficient of thermal expansion, axial, in. /in. /°F

E = modulus of elasticity, axial, psi (compressive for expansion and tensile for contraction)


Tc = temperature change, °F (Maximum operating temperature minus installation temperature for expansion. Installation temperature minus minimum operating temperature for contraction.)

Example 8-2: For the 2-in. nominal pipe of example 8-1, with a reinforced OD of2.375 in., the compressive modulus of elasticity Ec is 1.3 × 106 psi, and the tensilemodulus of elasticity is 1.72 × 106 psi. The pipeline is installed at 75°F and has amaximum operating temperature of 200°F and a minimum operating temperature of35°F. The coefficient of thermal expansion is 1.09 × 10–5.

Step 1. Calculate the temperature changes:

Tc = 200 − 75 = 125°F (for expansion)

Tc = 75 − 35 = 40°F (for contraction)



Step 2. Calculate the cross-sectional area:

A = π4

(OD2 − ID2) (8-6)

A = 0.7854 (2.3752 − 2.2352) = 0.507 in.2

Design calculations typically use only the reinforced dimensions. Resin-richsurfaces do not contribute significantly to the strength of the pipe.

Step 3. Calculate the end load using Eq 8-5:

EL = (1.09 × 10−5) (1.3 × 106) (0.507) (125)

= 898 lb (for expansion)

EL = (1.09 × 10−5) (1.72 ×106) (0.507) (40)

= 380 lb (for contraction)

When pipe lengths between anchors expand, the pipe undergoes compression.When contraction occurs, the pipe experiences tension.

8.5.2 Spacing Design—Anchoring and GuidingInstalling anchors at all directional and elevation changes serves to divide the systeminto straight runs. With anchors installed, guides are an economical method fordealing with expansion. The relatively low modulus of fiberglass pipe allows it toabsorb the thermal stresses as compressive stresses in the pipe wall. Compressivestresses from expansion may result in buckling unless the pipe is constrained at closeintervals to prevent columnar instability.

The equation to calculate maximum allowable guide spacing interval is:

Paste (Eq 8-7) (8-7)

Where:

LG = maximum distance between guides, ft

Eb = bending modulus of elasticity, axial, psi

Ec = compressive modulus of elasticity, axial, psi

I = moment of inertia, in.4

Ct = coefficient of thermal expansion, axial, in. /in. /°F

A = cross sectional area of reinforced pipe wall, in.2

Tc = temperature change, °F

Because the bending and compressive moduli are obtained from experimentaldata, the ratio Eb/Ec, using data representative of the minimum and maximum



operating temperatures, should be calculated. The lower value of the two calculationswill satisfy the interest of conservative design.

Compare guide intervals with the intervals for supports, then adjust guidespacing for a better match with support spacing. For example, adjust intervals so aguide replaces every second or third support. Remember, all guides act as modifiedsupports and must meet the minimum requirements for supports, anchors, andguides as prescribed in other sections of this chapter.

Example 8-3: Use the data from examples 8-1 and 8-2 and the followingadditional information to determine the maximum allowable guide spacing.

At 35°F, Eb = 2.2 × 106 psi and Ec = 1.3 × 106 psi

At 200°F, Eb = 1.3 × 106 psi and Ec = 0.6 × 106 psi

Step 1. Calculate I:

I = π

64 (OD4 − ID4)

I = π

64 (2.3754 − 2.2354)

I = 0.337 in.4

Step 2. Calculate Eb/Ec at temperature:

At 35°F, Eb/Ec = 2.2 × 106 / 1.3 × 106 = 1.69

At 200°F, Eb/Ec = 1.3 × 106 / 0.6 × 106 = 2.17

Use the 35°F data (lesser of the ratios).

Step 3. Calculate LG using Eq 8-7:

Paste Eq 8-7

8.5.3 Expansion Joint DesignExpansion joints may be used to absorb thermal expansion in long, straight piperuns. Various types of expansion joints are available and suitable for use withfiberglass piping systems. Because the forces developed during a temperature changeare relatively low compared with metallic systems, it is essential to specify anexpansion joint that activates with low force. Remember that fiberglass pipe willexpand more than most metallic systems. The required movement per expansion jointand the number of expansion joints may be greater for fiberglass systems.

The allowable activation force for expansion joints depends on both the thermalforces developed in the pipe and the support or guide spacing. Guide spacing at theentry of an expansion joint is typically 4 pipe diameters (first guide) and 14 pipediameters (second guide) from the inlet of the expansion joint (Figure 8-3). Theseguides and locations give proper alignment. The spacing of the remaining supportsshould remain within the maximum calculated interval.



The equation for calculating the allowable activation force is:

Pcr = π2 (Ec) (I)

LG2

× Sf(8-9)

Where:

Pcr = critical buckling force of pipe, lb

Ec = compressive modulus of elasticity, axial, psi, at operating temperature

I = moment of inertia, in.4

LG = support spacing interval, in.

Sf = safety factor to allow for material variations; recommend value of 0.9

Example 8-4: Compute the critical buckling force for the 2-in. nominal pipeusing the data from the prior examples (support spacing, LG = 7.5 ft) using Eq 8-9.

Pcr = (3.1416)2 (1.3 × 106) (0.337)

[ (7.5) (12) ]2 × 0.9

Pcr = 481 lb

NOTE: The pressure thrust must be considered. Pressure thrust is the designpressure times the area of the expansion joint.

In all applications, the activation force of the expansion joint must not exceedthe thermal end loads developed by the pipe. The cost and limited motion capabilityof expansion joints makes them impractical to use in many applications. In thesecases, loops, guide spacing, or short lengths of flexible hose can handle thermalexpansion. The expansion joint needs an anchor on both sides for proper operation.

Anchor* Anchor

Expansion Joints

Primary Guide

"A"

Secondary Guide

Anchor*"B"

*Anchor Load = _ (ID)2 × Internal Pressure4π

Reprinted with permisssion from Fiberglass Pipe Handbook, Fiberglass Pipe Institute, New York, N.Y.

Figure 8-3 Typical expansion joint installation

NOTE: A = 4 diameters; B = 14 diameters



8.5.4 Expansion Loop DesignExpansion loops flex to accommodate changes in length (Figure 8-4). This designmethod is used to calculate the stress developed in a cantilevered beam with aconcentrated load at the free end and ignores flexibility of the loop leg, the leg parallelto the line.

Two guides on both sides of each expansion loop ensure proper alignment. Therecommended guide spacing is 4 and 14 nominal pipe diameters. Additional guides orsupports should be located so the maximum spacing interval is not exceeded.

To design an expansion loop, use the following equation:

Paste (Eq 8-10) (8-10)

Where:

LA = length of the “A” leg, ft

Lc = length change, in.

Eb = bending modulus of elasticity, axial, psi

OD = outside diameter of pipe, in. (minimum)

K = cantilevered beam constant

= 0.75 for nonguided cantilevered beam

= 3.0 for a guided cantilever beam

allowable bending stress, psi (minimum Sf=8) σb = design

∆ L1Anchor AdditionalSupport

Pipe Run No. 1L2∆

Pipe Run No. 2

First Guide

Second Guide LengthLength Anchor

"B"

"A"


Figure 8-4 Expansion loop dimensions



Example 8-5: Calculate length of the expansion loop “A” leg required for the2-in. pipe, as in previous examples, with an allowable bending stress σb = 1,850 psi(8:1) and a calculated maximum length change of 4.0 in.

Paste Example 8-5

LA = 5.9 ft

The length of leg “B” is typically taken as half the length of leg “A.” For this casethen, “B” = (5.9)(0.5) = 2.95 ft.

If the maximum allowable bending stress of the fittings is greater than themaximum for the pipe, the bending moment of the fitting does not need to beconsidered. In other cases, the fitting manufacturer will provide allowable bendingmoments for the fittings. These values are used in Eq 8-11 to determine the “A” leglength. The results are compared and the larger value is used. Pipelines withheavy-wall pipe and relatively thin-wall fittings are most likely to require verificationof the LA dimension.

Paste (eq 8-11) (8-11)

Where:

Lc = length change, in. (maximum)

M = allowable elbow bending moment, lb -in.

NOTE: In some cases, the manufacturer may require anchors at all fittings. Forexample, mitered fittings and/or large diameter fittings may have allowable bendingstresses below that of the pipe. In these cases, thermal expansion procedures may belimited to the use of anchors and guides or expansion joints if the bending moment isnot available.

8.5.5 Direction ChangesIn some installations, system directional changes can perform the same function asexpansion loops. Directional changes that involve some types of fittings, such assaddles, should not be used to absorb expansion or contraction. The bending stressesmay cause fitting failure. Stress in the pipe at a given directional change depends onthe total change in length and the distance to the first secure hanger or guide pastthe directional change. In other words, the required flexible leg length is based on themaximum change in length.

Recommended support or guide spacing cannot be disregarded. However, flexibleor movable supports, such as strap hangers, can provide support while allowing thepipe to move and absorb the changes in length. Supports must prevent lateralmovement or pipe buckling.

Where large thermal movements are expected, a short length of flexible hoseinstalled at a change in direction will absorb some of the line movement. This methodof handling thermal expansion is usually the most economical means of compensatingfor large displacements when the guide spacing method cannot be used. Hose



manufacturers provide specifications giving the minimum bend radius, chemicalcompatibility, temperature, and pressure rating of a particular flexible hose.

The equation for calculating the length of the flexible pipe leg (i.e., the distanceto the first restraining support or guide) is:

Where:

Lsh = length from direction change to the first secure hanger, ft

Example 8-6: Calculate the value of Lsh using the 2-in. nominal diameter pipefrom previous examples.

This type of analysis usually neglects torsional stresses. Allowable bendingstress is much lower than the allowable torsional stress. Therefore, bending of thepipe leg as shown in Figure 8-5 will typically absorb pipe movement. However, theunanchored leg must have a free length equal to or greater than Lsh as calculatedfrom Eq 8-12.

8.6 SUPPORTS, ANCHORS, AND GUIDES Six basic rules control design and positioning for supports, anchors, and guides.

8.6.1 Rule 1. Avoid Point LoadsUse curved supports fitted to contact the bottom 120 degrees of the pipe and thathave a maximum bearing stress of 85 psi (586 kPa). Do not allow unprotected pipe topress against roller supports, flat supports, such as angle iron or I-beams, or U-bolts.

Lc

Lsh

Figure 8-5 Directional change



Do not allow pipe to bear against ridges or points on support surfaces. Use metal orfiberglass sleeves to protect pipe if these conditions exist.

8.6.2 Rule 2. Meet Minimum Support DimensionsStandard pipe supports designed for steel pipe can support fiberglass pipe if theminimum support widths provided in Table 8-2 are met. Supports failing to meet theminimum must be augmented with a protective sleeve of split fiberglass pipe ormetal. In all cases, the support must be wide enough so that the bearing stress doesnot exceed 85 psi (586 kPa).

Sleeves augmenting supports must be bonded in place using adhesives stable atthe system’s maximum operating temperature.

Prepare all pipe and sleeve bonding surfaces by sanding the contacting surfaces.

8.6.3 Rule 3. Protect Against External AbrasionIf vibrations or pulsations are possible, protect contacting surfaces from wear(Figure 8-6). When frequent thermal cycles, vibrations, or pulsating loadings affectthe pipe, all contact points must be protected. This is typically accomplished bybonding to the wall a wear saddle made of fiberglass, steel, or one-half of a section ofthe same pipe.

8.6.4 Rule 4. Support Heavy Equipment IndependentlyValves, and other heavy equipment, must be supported independently in bothhorizontal and vertical directions (Figure 8-7).

8.6.5 Rule 5. Avoid Excessive BendingWhen laying lines directly on the surface, take care to ensure there are no excessivebends that would impose undue stress on the pipe.

Table 8-2 Minimum support width for 120° contact supports

Pipe Size Minimum Support Width

in. mm in. mm1 25 0.88 22.41.5 40 0.88 22.42 50 0.88 22.43 80 1.25 31.84 100 1.25 31.86 150 1.50 38.18 200 1.75 44.5

10 250 1.75 44.512 300 2.00 50.814 350 2.00 50.816 400 2.50 63.5

NOTE: Table is based on maximum liquid specific gravity of 1.25.



8.6.6 Rule 6. Avoid Excessive Loading in Vertical RunsSupport vertical pipe runs as shown in Figure 8-8. The preferred method is to designfor “pipe in compression.” If the “pipe in tension” method cannot be avoided, take careto limit the tensile loadings below the recommended maximum tensile rating of thepipe. Install guide collars using the same spacing intervals used for horizontal lines(Figure 8-8).

8.6.7 GuidesThe guiding mechanism must be loose to allow free axial movement of the pipe.However, the guides must be attached rigidly to the supporting structure so that thepipe moves only in the axial direction (Figure 8-9).

All guides act as supports and must meet the minimum requirements forsupports. Refer to Sec. 8.6.3 if thermal cycles are frequent.

Reprinted with permisssion from Fiberglass Pipe Handbook, Fiberglass Pipe Institute, New York, N.Y.

Figure 8-8 Vertical support

Reprinted with permission from Fiberglass PipeHandbook, Fiberglass Pipe Institute, New York, N.Y.

Figure 8-7 Steel wear protection cradle


Figure 8-6 Fiberglass wear protection cradle



8.6.8 AnchorsAn anchor must restrain the movement of the pipe against all applied forces. Pipeanchors divide a pipe system into sections. They attach to structural material capableof withstanding the applied forces. In some cases, pumps, tanks, and other similarequipment function as anchors. However, most installations require additionalanchors where pipe sizes change and fiberglass pipe joins another material or aproduct from another manufacturer. Additional anchors usually occur at valvelocations, changes in direction of piping runs, and at major branch connections.Saddles and laterals are particularly sensitive to bending stresses. To minimizestresses on saddles and laterals, anchor the pipe on either side of the saddle or anchorthe side run.

Figure 8-10 shows a typical anchor. Operating experience with piping systemsindicates that it is a good practice to anchor long, straight runs of aboveground pipingat approximately 300 ft (91 m) intervals. These anchors prevent pipe movement dueto vibration or water hammer.

One anchoring method features a clamp placed between anchor sleeves or a setof anchor sleeves and a fitting. The sleeves bonded on the pipe prevent movement ineither direction. Sleeve thickness must equal or exceed the clamp thickness. Toachieve this, it often is necessary to bond two sleeves on each side of the clamp.Anchor sleeves are usually one pipe diameter in length and cover 180° ofcircumference. Anchors act as supports and guides and must meet minimumrequirements for supports.

8.6.9 SupportsTo prevent excessive pipe deflection due to the pipe and fluid weight, supporthorizontal pipe (see Figure 8-11) at intervals determined by one of the followingmethods.

8.6.9.1 Type I. Pipe analyzed as simply supported single spans (two supportsper span length) with the run attached to a fitting at one end, or any other section of


Figure 8-9 Guide support


Figure 8-10 Anchor support

SupportMember

Steel Cradle

Allows Movement in Axial Direction Only

Typical Guide

Repair Couplingor FRP Buildup

Clamp, Snugbut Not Tight

Restrains Pipe Movement in All Directions

Typical Anchor



less than three span lengths. Beam analysis for other types of spans, such as a sectionadjacent to an anchor, is sometimes used to obtain a more accurate span length.However, the following equation is more conservative.

(8-13)

Where:

Ls = unsupported span length, in.

dm = allowable midpoint deflection, in. (0.5 in. is typical for fiberglass)

W = Pw + Wf, lb/lin in.

Pw = pipe weight, lb/lin in.

Wf = fluid weight, lb/lin in.

Wf = ρVp/12

Lh = linear length (use 1.0 ft to obtain lb/ft)

ρ = density, lb/ft3

Vp = pipe volume per lin ft, ft3/ft

Vp = (π/(ID/12)2) (Lh/4)

I = π/64 (OD4 − ID4 )

ID = inside diameter, in.

OD = outside diameter, in.

When mid-span deflection dm exceeds 0.5 in. (13 mm), check with the pipemanufacturer for other considerations, such as the allowable bending stress orbearing stress. When the mid-span deflection is limited to 0.5 in. (13 mm), thebending stress on the pipeline is typically below the allowable bending stress for the

Support Member

Steel Cradle

Pipe Can Move Sidewaysand Axially


Figure 8-11 Typical support



pipe. For installations that result in more than 0.5 in. (13 mm) of mid-span deflection,the 8:1 safety factor on bending stress has proven to be sufficient to compensate forthe combination of bending stress and the longitudinal stresses resulting frominternal pressure.

In fact, cyclic bending tests have shown that the stresses are not additive asexpected and that the 8:1 safety factor is conservative. (Cyclic bending tests consist ofcyclic pressure testing of pipe bent to stress levels at or above the design bendingstress.)

For low stiffness pipe with a relatively thin wall, the local bearing pressure atsupports is often significant. Supports for this application usually require 180°contact and follow a conservative design allowable bearing pressure (45 psi [310 kPa])compared with the typically permitted 85 psi (586 kPa) used for smaller diameter,higher stiffness pipe. Because pipe design differs among manufacturers, follow thesupplier’s recommendations for the product and system.

Example 8-7: Using the 2-in. nominal pipe from previous examples and thefollowing steps, calculate the allowable span length Ls:

Step 1. Calculate the pipe volume using Eq 8-14:

Vp = 3.1416 (2.235

12)2 (1.0)

4

Vp = 0.0272 ft3/ft

Step 2. Calculate W:

p = (6.24) (1.05) = 65.5

Wf = (65.5) (0.0272) = 1.78 lb/ft

W = 0.4 + 1.78 = 2.18 lb/ft

Step 3. Calculate Ls using Eq 8-13:

8.6.9.2 Type II. Pipe analyzed as a continuous beam—three spans—all loaded.

(8-15)

8.6.9.3 Type III. Pipe analyzed as a continuous beam—four spans—all spansloaded.

(8-16)



8.6.9.4 Type IV. Pipe analyzed as a beam fixed at both ends—uniformlydistributed loads.

(8-17)

Supports must also meet the minimum requirements for supports described inSec. 8.6.1 through Sec. 8.6.6.

NOTE: In cases where the wall thickness to diameter ratio is low, the possibilityof buckling failures at the supports is a concern. This may require the use of empiricalequations and special bearing stress calculations that were determined or verified bytesting.

8.7 BENDING ____________________________________________The minimum bending radius for fiberglass pipe usually results from a design stressthat is one-eighth of the ultimate short-term bending stress. Certain fittings, such assaddles and laterals, may be more susceptible to bending failure than other types.(Consult the manufacturer for recommendations and limitations.) The equation forcalculating the minimum bending radius is:

Rm = (Eb) (OD)(24) (Sb) (8-18)

Where:

Rm = minimum allowable bending radius, ft

Example 8-8: Use the 2-in. nominal pipe, used in previous examples, andEq 8-18 to calculate the minimum bending radius at 75°F:

Rm = (2.2 × 106) (2.375)

(24) (1,850)

Rm = 117.7 ft

Because material properties vary with temperature, the allowable minimumbending radius will also vary.

8.8 THERMAL CONDUCTIVITY ____________________________The thermal conductivity of fiberglass pipe wall is approximately 1 percent that ofsteel. However, in most heat transfer situations, the heat loss or gain for pipe iscontrolled by the resistance to heat flow into the surrounding media (i.e., air or soil)rather than the thermal conductivity of the pipe. This reduces the insulating effect ofa relatively thin fiberglass pipe wall. For this reason, thermal insulation tables forsteel pipe can be used to size the insulation for most fiberglass pipelines.



The coefficient of thermal conductivity varies for different types of fiberglasspipe. A typical value for an epoxy resin pipe is 2.5–3.0 Btu/(h) (ft2) (°F)/in. (0.36–0.43W/m-K). A typical value for polyester or vinyl ester resin pipe is 1.0–1.5 Btu/(h) (ft2)(°F)/in. (0.14–0.22 W/m-K).

8.9 HEAT TRACING ______________________________________Both steam tracing and electrical heating tapes are acceptable techniques for heatingfiberglass pipe. When using either method, three criteria govern the maximumelement temperature:

1. The average wall temperature must not exceed the temperature ratingof the pipe.

2. The maximum tracing temperature must not be more than 100°F(38°C) above the maximum rated temperature of the pipe.

3. The maximum recommended chemical resistance temperature of thepipe must not be exceeded at the inside wall of the pipe.

Application of these three limits is best explained by example.Example 8-9: What is the maximum heat tracing temperature allowed to

maintain a 50 percent caustic solution at 95°F inside a fiberglass pipe with 210°Fmaximum temperature rating? The published chemical resistance temperature forthis application is 100°F.

Step 1:

For criteria 1, the following equation is applicable:

At = (Ti + Tt)/2 (8-19)

Where:

At = average wall temperature, °F

At = (95 + Tt)/2 = 210°F

Ti = inside wall temperature,°F

Tt = heat tracing temperature, °F

Tt = 325°F maximum

Step 2:

For criteria 2, the following equation is used:

Tt = TR + 100°F (8-20)

Where:

TR = maximum rated temperature of pipe, °F

Tt = 210°F + 100°F = 310°F



Step 3:

The maximum tracing element temperature is the lesser of the values calculatedusing Eq 8-19 and Eq 8-20. In this case the value is 310°F.

The maximum tracing element temperature using this methodology applies onlyto applications involving flowing, nonstagnant, fluid conditions. For stagnantconditions, the maximum allowable trace element is the chemical resistancetemperature of the pipe. For this example, Tt # 100°F.

Step 4:

For criteria 3, it is necessary to check the manufacturer’s published data todetermine the maximum recommended chemical resistance of the pipe for thisapplication. This value is compared with the inside wall temperature Ti. Thepublished value must be greater than Ti.

In example 8-9, the maximum allowable trace temperature is 100°F.

8.10 CHARACTERISTICS AND PROPERTIES _________________The characteristics and properties for fiberglass pipe are different from thosetypically used for metallic pipes.

8.10.1 Design Pressure or StressDesign stresses for pipe internal pressure are based on ASTM D2992, as shown inTable 8-1. The internal operating pressure for fittings is generally based onone-fourth of the ultimate short-term failure pressure (ASTM D1599).

8.10.2 Modulus of ElasticityThe modulus of elasticity for fiberglass pipe is different in the axial and the hoopdirections because the pipe is an anisotropic composite material. Also, the tensile,bending, and compressive modulii may differ significantly, thus it is important to usethe correct value. The modulii depend upon the type of resin, amount of glass, andorientation of the glass filaments. Precise values for the moduli for specific conditionsof loading and temperature should come from the manufacturer. Typical values areoften obtained by drawing a tangent to the stress strain curve at the point equal toone-fourth of ultimate failure load. The moduli may also vary with temperature.

8.10.3 Allowable Tensile or Compressive LoadsTypically, the allowable design stress is 25 percent of the ultimate short-term failureloads. These stress values can be used with the minimum reinforced wall thickness(area) to calculate the allowable maximum loads.

8.10.4 Bending LoadsUltimate beam stress is determined by using a simple beam with a concentrated loadapplied to the center to achieve short-term failure. The allowable design stress is thenestablished by application of at least an 8:1 factor of safety to the ultimate failurevalue. The 8:1 factor is selected to compensate for combined loading that occurs inpressure piping applications.

The bending modulus is determined from a test by measuring mid-spandeflections of a simply supported beam with a uniformly distributed load over time,usually not less than six weeks. Allowable bending stress and the bending modulus of



elasticity may vary with temperature. Values must account for the temperatureextremes expected to occur in the piping application under consideration.

8.10.5 Poisson’s RatioBecause fiberglass piping is an anisotropic material, Poisson’s ratio varies dependingon loading conditions. For example, Poisson’s ratio in the transverse (hoop) directionresulting from the axial loading is not the same as Poisson’s ratio in the axialdirection resultant from transverse (hoop) loading.

8.10.6 Vacuum or External PressureFiberglass pipe can convey materials under vacuum. The ability of fiberglass pipe toresist collapse pressure depends on the pipe stiffness, which is a function of the pipesize, method of manufacture, ratio of diameter to wall thickness, and the rawmaterials used.

The external pressure resistance of fiberglass pipe is determined by testing inaccordance with ASTM D2924. This standard test method identifies two short-termfailure pressures:

• Buckling failure pressure—the external gauge pressure at which bucklingoccurs.

• Compressive failure pressure—the maximum external gauge pressure thatthe pipe will resist without transmission of fluid through the wall.

Scaling constants are used to relate the test data to pipe sizes not tested.Typically, the manufacturer’s recommended value for collapse pressure is

33 percent to 75 percent of the pipe ultimate short-term external failure pressure(ASTM D2924). The manufacturer’s recommended values should be used for designpurposes.

8.10.6.1 Buckling scaling constant.

K = P

Ec

rt

3 (8-21)

Where:

K = buckling scaling constant

P = external collapse pressure, psig

Ec = circumferential modulus of elasiticity, psi

r = mean reinforced wall thickness, in.

t = minimum reinforced wall thickness, in.

8.10.6.2 Compressive scaling constant.

C = Pc (OD − t)

2t(8-22)

Where:

C = compressive scaling constant

psiPc = pressure at failure,



REFERENCES ______________________________________________

Standard for Fiberglass Pressure Pipe. 1995.ANSI/AWWA C950. Denver, Colo.:American Water Works Association.

Standard Practice for Obtaining Hydro-static or Pressure Design Basis for‘Fiberglass’ (Glass-Fiber-ReinforcedThermosetting-Resin) Pipe and Fit-tings. 1991. ASTM D2992. West Con-shohocken, Pa.: American Society forTesting and Materials.

Standard Test Method for Beam Deflectionof ‘Fiberglass’ (Glass-Fiber-ReinforcedThermosetting-Resin) Pipe Under FullBore Flow. 1995. ASTM D2925. WestConshohocken, Pa.: American Societyfor Testing and Materials.

Standard Test Method for Coefficient ofLinear Thermal Expansion of PlasticsBetween 2 30 Degrees C and 30 De-grees C. 1991. ASTM D696. WestConshohocken, Pa.: American Societyfor Testing and Materials.

Standard Test Method for CompressiveProperties of Rigid Plastics (Metric).1991. ASTM D695. West Consho-hocken, Pa.: American Society forTesting and Materials.


Standard Test Method for External PressureResistance of ‘Fiberglass’ (Glass-Fiber-Reinforced Thermosetting-Resin) Pipe.1993. ASTM D2924. West Consho-hocken, Pa.: American Society for Test-ing and Materials.

Standard Test Method for Longitudinal TensileProperties of ‘Fiberglass’ (Glass-Fiber-Re-inforced Thermosetting-Resin) Pipe andTube. 1990. ASTM D2105. West Consho-hocken, Pa.: American Society for Testingand Materials.

Standard Test Method for Short-Time Hy-draulic Failure Pressure of Plastic Pipe,Tubing, and Fittings. 1988. ASTMD1599. West Conshohocken, Pa.: Ameri-can Society for Testing and Materials.

Standard Test Method for Tensile Proper-ties of Plastic. 1994. ASTM D638.West Conshohocken, Pa.: AmericanSociety for Testing and Materials.



Joining Systems, Fittings, and Specials

JOINING SYSTEMS, FITTIN GS, AN D SPECIALS

9.1 INTRODUCTION ______________________________________Several types of joining systems are available for use with fiberglass pressure pipe.Many of the systems permit joint angular deflection. Some joining systems may bedesigned to resist longitudinal thrust forces. Fittings and specials are available in arange of styles and configurations and are fabricated by a number of differentmanufacturing methods.

9.2 FIBERGLASS PIPE JOINING SYSTEMS CLASSIFICATION ___There are two general joint classifications: unrestrained and restrained.

9.2.1 Unrestrained Pipe JointsThese joints can withstand internal pressure but do not resist longitudinal forces.They rely on elastomeric gaskets to provide the seal. Typically, these joints can bedisassembled without damage.

Fiberglass Couplings or Bell and Spigot Joints. These joints use anelastomeric seal located in a groove on the spigot or in the bell as the sole means toprovide fluid tightness.

Mechanical Coupling Joint. These joints use mechanically energized elas-tomeric gasket seals to join two pieces of pipe. The mechanical coupling techniqueapplies to plain end pipe.

9.2.2 Restrained Pipe JointsThe restrained pipe joints can withstand internal pressure and resist longitudinalforces.

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Joints that may later be disassembled without damage include:• coupling, or bell and spigot with a restraining device• flange• mechanicalJoints that cannot be disassembled without damage or cutting apart include:• butt and wrap• wrapped bell and spigot• bonded bell and spigot

9.3 GASKET REQUIREMENTS _____________________________Gaskets used with fiberglass pipe joining systems should conform to the requirementsof ASTM F477. The gasket material composition must be selected to be compatiblewith the intended environment as agreed upon between the purchaser and seller.

9.4 JOINING SYSTEMS DESCRIPTION ______________________In this section, many of the joining systems available with fiberglass pressure pipeare described; however, the details of every type of joining system available are notincluded. Versatility of manufacture permits differences in configuration andgeometry while meeting performance requirements. Users should contact the pipemanufacturer to obtain specific details on joints and joint performance.

9.4.1 Adhesive-Bonded JointsThree types of adhesive-bonded joints are available:

• a joint using a tapered bell and a tapered spigot (Figure 9-1)• a straight bell and straight spigot joint (Figure 9-2)• a joint using a tapered bell and a straight spigot (Figure 9-3)Adhesive-bonded joints are generally available for pipe up through 16 in.

(400 mm) diameter.

9.4.2 Reinforced-Overlay JointsThe butt and wrap joint typically consists of two squared pipe ends that have beenprepared for joining by roughening the outside surface in the joint area. The pipes are

Source: Smith Fiberglass Products Inc., Little Rock, Ark.

Figure 9-1 Tapered bell and spigot joint



then abutted end to end, aligned on the same centerline, and the joint overwrappedwith layers of resin-impregnated glass fiber materials. Each layer becomesincreasingly wider to provide a buildup that accommodates internal pressure andlongitudinal forces. Basic joint construction is shown in Figure 9-4, with the finishedjoint illustrated in Figure 9-5. A variation of this joint is illustrated in Figure 9-6, inwhich the pipe ends are tapered. Bell and spigot joints are sometimes overlaid asshown in Figure 9-7. In this system the bell aids in alignment during the overlayoperation. Internal overlays are also used to improve joint performance but aregenerally only possible on larger diameter pipe that allows the installer to workinside the pipe during installation.

9.4.3 Gasket-Sealed Joints9.4.3.1 Bell and spigot. Figure 9-8 and Figure 9-9 illustrate a bell and spigotgasketed joint using a single gasket design. Figure 9-10 and Figure 9-11 illustrate abell and spigot gasketed joint using double gasket design. The double gasket design isgenerally only used with larger diameter pipe. By inserting ports in the spigot

AdhesiveBonding Area

Pipe PipeBell

Adhesive Fillet

Pipe

Figure 9-2 Straight bell and straight spigot joint

Figure 9-3 Tapered bell and straight spigot joint

JOINING SYSTEMS, FITTINGS, AND SPECIALS 127


��

BlendEdges

BlendEdges

RoughenedArea Butted Joint

End A


Figure 9-4 Overlay joint construction


Figure 9-5 Overlay joint

Reprinted with permission from Fiberglass Pipe Handbook,Fiberglass Pipe Institute, New York, N.Y.

Figure 9-6 Tapered ends overlay joint

��

��

Overlay


Figure 9-7 Bell and spigot overlay joint



between the two gaskets, a test of the sealing integrity of the gaskets can beconducted immediately after assembly using hydrostatic or pneumatic pressure.

9.4.3.2 Coupling. Figure 9-12 and Figure 9-13 show two styles of gasketedcoupling joints. The joint in Figure 9-12 uses a gasket mechanically bonded or moldedin the coupling. Figure 9-13 shows a coupling with gaskets retained in grooves.

9.4.3.3 Restrained gasketed joints. None of the gasketed joints shown inFigures 9-8 through 9-13 provide longitudinal restraint, although they can be modified ina variety of ways to do so. Figure 9-14 illustrates a bell and spigot joint with a gasket andrestraining elements. The restraining element is a mechanically loaded locking ringdesigned to expand and allow the spigot to enter the bell and then contract to lock on ashoulder of the spigot outside diameter. Figure 9-15 illustrates a coupling joint with apair of gaskets and restraining elements. The shape and the material used for therestraining element can vary. Both metallic and shear resistant plastic materials areused for this device. Figure 9-16 illustrates a bell and spigot joint with a gasket and athreaded connection joint restraining element. An advantage of many of the restrainedjoints is that they can be disassembled for removal or repair.

9.4.4 Mechanical JointsThere are numerous mechanical joints available for use with fiberglass pipe,including flanges, threaded joints, and commercially available proprietary joints.Pressure-rated flanges are common in the installation of all sizes of fiberglass


Figure 9-8 Single gasket bell and spigot joint

Source: Price Brothers Company, Dayton, Ohio.

Figure 9-9 Single gasket spigot


Figure 9-11 Double gasket spigot

Source: Smith Fiberglass Products, Little Rock, Ark.

Figure 9-10 Double gasket bell and spigot joint



pressure pipe. Fiberglass flanges have bolting dimensions consistent with standardANSI/ASME pressure classes of bolted flanges. Fiberglass flanges are produced byhand lay-up, filament winding, and compression molding.

Project conditions often dictate mating a fiberglass flange with a metallic flangeon a pump, valve, or metallic pipe. Figure 9-17 depicts a fiberglass flange to fiberglass


Figure 9-12 Gasketed coupling joint


Figure 9-13 Gasketed coupling joint


Figure 9-14 Restrained gasketed bell andspigot joint

Source: Old Hope Corguard Inc., (former subsidiary ofPrice Brothers Company, Dayton, Ohio).

Figure 9-17 Fiberglass f lange to f iberglassand steel f lange joint


Figure 9-15 Restrained gasket coupling joint

Figure 9-16 Restrained gasketedthreaded bell and spigot O-ring joint

Spigot

Coupling

ElastomericGasket

Locking KeyCoupling

O-Ring Gasket

��

Bell and Spigot O-ring Joint Elastomeric“O” ring

ElastomericBearing Ring

Threaded Nutfor Make-upand Thrust Restraint

Gasket

Flange

Steel



flange joint and a fiberglass flange to steel flange joint. Figure 9-18 shows the joiningof fiberglass flanges to steel flanges to complete a valve connection.

Gaskets used with fiberglass flanges may be flat-faced or O-rings contained in agroove in the flange face (see Figure 9-19). The use of O-ring seals has been found tobe very effective, particularly for large diameters, because positive seal is obtainedwithout excessive bolt torque.

Figure 9-20 shows one common mechanically coupled joint where the seal isaccomplished on the outside surface of the pipe. This type of joint does notaccommodate longitudinal forces. Care must be taken to not over torque this type ofmechanical joint because excessive torque can damage some fiberglass pipe.

9.5 ASSEMBLY OF BONDED, THREADED, AND FLANGED JOINTS _______________________________________________

Bonded, threaded, and flanged fiberglass pipe joints require the use of techniques andequipment that may be considerably different than those used with other pipingmaterials. Although the pipe manufacturer’s instructions must always be followed, abrief general overview is given in the following sections.


Figure 9-18 Fiberglass f langes to f langedsteel valve connection


Figure 9-19 Fiberglass f lange with groovedface for O-ring seal

Sleeve FlangeFlange

Gaskets Pipe (OD)

Figure 9-20 Mechanical coupling joint



9.5.1 Layout and Preparation All installation crew members must be familiar with the installation proceduresprovided by the manufacturer.

Inspection of the pipe and fittings for damage that may have occurred duringhandling is important. Proper storage and handling procedures are discussed inchapter 10 and provided by the manufacturers.

The crew size requirement varies from one type of installation to another. Atypical crew for 2 to 4 in. (50 to 100 mm) diameter pipe installations is two or threemembers, while installations involving large diameters can require crews of four ormore members.

9.5.2 Tool and Equipment RequirementsTool and equipment requirements vary as the pipe size and type of joint change;however, the following are general guidelines.

For cold weather installations, heating devices such as electric heating collars,heated portable buildings (plastic huts), hot air blowers, etc. are necessary to ensureproper installation of bonded joints.

Machining equipment such as tapering tools, disk sanders, etc. are required forend preparation on bonded joint systems. The specialized machines, such as taperingtools, are often available from the manufacturer. Disk grinders, belt sanders, andother more common equipment are generally supplied by the installer.

Pipe cutting equipment usually consists of fine-tooth saws and/or saws withcarbide grit abrasive blades. Saw blades and hole saws typically used for wood are notsuitable; however, blades used for masonry and/or tiles are usually abrasive typeblades that will be suitable for fiberglass pipe. NOTE: Cutting and/or grindingoperations can generate dust or cutting chips that are irritating to the skin, upperrespiratory tract, and eyes. Because these materials are irritating, good ventilationfor the installation crew should be used to prevent overexposure. A nuisance dustbreathing filter should be used when working in areas where wind and dust arepresent. Tool operators should wear heavy cotton clothing, including long-sleeveshirts, which protect the skin from the dust. Eye protection is often required for tooloperators. Contact your local regulatory agency or Occupational Safety and HealthAdministration (OSHA) office for specific requirements on the use of respirators,protective clothing, and any additional safeguards.

Pipe chain vises and pipe stands are designed for metal piping. Therefore, it isnecessary to provide protective pads, such as rubber cushions, to protect the pipe frompoint loading and/or impact damage. Protective pads are sometimes required when usingcome-a-longs or other tools that can create bearing and/or point loading damage.

For threaded joints, special wrenches and/or strap wrenches are recommended bymost manufacturers. CAUTION: Improper use of strap wrenches can cause pointloading.

Some tools can be used with a power drive, such as a Rigid 700 or a Rigid 300.The contractor may have to obtain a different adapter for the power drives. Forexample, threaded adapters used by many contractors are not used for fiberglasspipe. A typical adapter consists of a 1-in. (25-mm) drive socket that fits a 15⁄16-in.(24-mm) square drive.

Miscellaneous equipment such as a wrap-around, felt tip marking pens,hammers (metal and rubber), and adjustable pipe stands are typical items requiredfor installation.



9.5.3 Bonded Joint AssemblyBecause there are many different types of joints available, detailed instructions arebeyond the scope of this manual. It is essential that manufacturer’s instructions beobtained for each type of joint being installed. The following are general guidelines.

Clean bonding surfaces are required for proper adhesion of adhesives and/orresins. In some cases, a cleaning operation, such as washing and using cleaningsolvent, is recommended. In all cases, avoid contamination that will leave dirt, oil,grease, fingerprints, etc., on surfaces that require adhesive or resin applications.Thoroughly mix the adhesive or resin and follow all safety precautions that areincluded with the materials. In most cases, the adhesive materials are preweighedand it is not possible to “split a kit.”

Shelf (storage) life and working (pot) life will vary from one type of resin toanother. If the mixture is setting up too fast or not at all, consult the manufacturer todetermine the best storage conditions, shelf life, and typical working life.

End preparation varies for the different joints. However, a clean, machinedsurface is generally required for application of adhesive or resin. The machiningoperation may involve sanding or grinding with special tools. For general sandingoperations, a coarse (24 or less) grit sandpaper is better than a fine grit.

Application of adhesives and/or resins normally requires a “wetting” process (i.e.,the materials should be applied in a manner that increases the penetration—andbonding—of the resins to the substrate), for example, using pressure on a paintbrushto apply resin to a machined surface.

Cure times vary and not all mixtures are properly cured when they have set up (orare hard to the touch). The proper mixing and curing procedures of the manufacturermust be followed to ensure maximum physical strength and proper chemical resistancefor the system. CAUTION: If mixture becomes warm and starts to cure in the container,discard immediately. Do not use this material to assemble a joint.

In some cases, the application of heat to speed up or ensure completion of thecuring process is necessary. CAUTION: Allow a heated joint to cool until it iscomfortable to the touch before any stress is applied to the joint. Any stresses on thepipe due to bending or sagging should be relieved prior to heat cure.

9.5.4 Threaded JointsConnecting to other systems is typically accomplished with mechanical connections,threaded adapters (National Pipe Threads), reducer bushings (National PipeThreads), grooved adapters, or flanges. Flange patterns are usually 150 lb (68 kg) or300 lb (136 kg) bolt circle for small diameter systems and 125 lb (57 kg) bolt circle forlarger diameter systems (above 24 in. [600 mm]).

Before making up threaded connections, inspect the threads. Do not use fittingswith damaged threads. Inspect all metal threads. Remove any burrs and reject metalthreads that have notches (grooves) that are near the end of the threads. The quality ofmetal threads is a concern when mating to fiberglass threads that require a low torquelevel. The quality of the metal threads will often have little or no effect on metal to metalconnections because the use of additional torquing force may seal a leak. Fiberglass tosteel connections are more likely to leak if the steel threads are in poor condition.

Unless a union is used, threaded adapters should be threaded into the othersystem before assembly of the fiberglass piping. Best results will be obtained using astrap wrench and a solvent-free, soft-set, nonmetallic thread lubricant. If threadsealing tapes are used, improper installation of the tape, such as using thick layers of



tape, must be avoided to prevent damage to the fiberglass threads. In all cases,tighten the fiberglass threads as if they were brass or other soft material.

9.5.5 Flanged JointsMost fiberglass flanges are designed for use against a flat surface; therefore, it maybe necessary to use spacers or reinforcement (back up) rings for connections to metalflanges, valves, pumps, etc. Fiberglass flanges require the use of flat washers on allbolts and nuts. In most cases, the type of gasket is specified by the manufacturer. Forexample, a full face gasket with a Shore “A” durometer rating of 60 to 70 is a typicalrecommendation. Gaskets made from polytetrafluoroethylene (PTFE)* and polyvinylchloride (PVC) usually have higher durometer ratings and may not seal at the torquelevels required for fiberglass installations.

9.5.6 Safety PrecautionsTesting with air or gas is not recommended because of the safety hazards involved. Thelight weight, flexibility, and elasticity of fiberglass pipe create different conditions thanare present with steel pipe. If a catastrophic failure occurs in a fiberglass system, thesystem would be subject to considerable whipping and other shock-induced conditionsdue to the sudden release of stored energy. The recommended procedure is to conducta hydrostatic pressure test.

9.6 FITTINGS AND SPECIALS _____________________________Fiberglass fittings and specials are available over a wide range of diameters,pressures, and configurations. Fittings and specials are made by compressionmolding, filament winding, cutting and mitering, and contact molding.

9.6.1 Compression MoldingCompression molding is generally used for fittings up to 16 in. (400 mm) diameter.Figure 9-21 and Figure 9-22 illustrate the range of configurations available for usewith plain end or flanged joints, for pressure applications of less than 500 psi

Figure 9-21 Compression molded fittings Figure 9-22 Flanged compression molded fittings


* Polytetrafluoroethylene (PTFE) is commonly referred to by the trade name Teflon.


(3,447 kPa). In this process, a weighed glass/resin mixture is placed in a multipiecemold. The mold pieces are then held together with high pressure while thetemperature is increased to cause curing. Molded fittings are cost-effective for lowpressure, small diameter applications where a large number of fittings are required.

9.6.2 Filament WindingFilament winding can produce fittings with higher mechanical strength than ispossible with molded fittings. In this process, resin-impregnated glass fibers arewound onto a fitting jig. The process may also include the use of woven rovings and/orglass mat. After winding and curing, the fitting is removed from the jig forpost-production processing.

9.6.3 Cut and Miter ProcessThe cut and miter process is extremely versatile for making the full range ofdiameters, standard and special shapes, and custom designed fittings. Figure 9-23shows a sampling of the fittings that are routinely made from cut and miteredsections. Fabrication of the fittings and specials starts with the production of pipethat is cut and assembled into the desired configuration.

Figure 9-23 Mitered fitting configurations

0˚– 30˚ 31˚– 60˚Mitered Elbows

61˚– 90˚ Wye

Concentric Reducer

Eccentric ReducerCrossTee

L L

Fitting Connected to End of Pipe Fitting Within Length of Pipe



Cut and mitered fittings also can be made by cutting pipe sections to the desiredform. Pieces are joined together with contact molding techniques using choppedstrand and woven roving reinforcement. Surface preparation before bonding isessential to ensure good adhesion between surfaces and the contact molded laminate.The fitting should resist the same loading conditions as the pipe.

Figures 9-24 through 9-28 show a variety of fiberglass fittings and specialsduring fabrication and on installation sites.


Figure 9-24 Mitered fitting


Figure 9-25 Mitered fitting fabrication


Figure 9-26 Mitered fittings




Figure 9-27 Mitered fitting field fabrication


Figure 9-28 Fittings field assembly



9.6.4 Contact MoldingContact molding (including spray-up) may be used to produce fittings directly.

9.7 SERVICE LINE CONNECTIONS _________________________Service line connections are typically made using tapping saddles. Consult individualpipe manufacturers for procedures applicable to specific products.

REFERENCES _____________________________________________Standard Specification for Elastomeric Seals

(Gaskets) for Joining Plastic Pipe.1995. ASTM F477. West Conshohocken,Pa.: American Society for Testing andMaterials.



Shipping, Handling, Storage, and Repair

SHIPPIN G, HANDLING, STORAGE, AND REPAIR

10.1 INTRODUCTION _____________________________________Fiberglass pipes encompass a wide range of diameters (1 in. to 144 in. [25 mm to3,600 mm]) with an equally wide range of wall thicknesses (from less than 0.1 in. tomore than 3 in. [3 mm to 80 mm]). Furthermore, the wall laminate constructions andcharacteristics vary sufficiently to exhibit significantly different behaviors. Due tothis wide variation in design and material characteristics, the requirements foracceptable shipping, handling, and storage are also somewhat variable. Consult themanufacturer for procedures specific to its products.

Despite the many differences, there are also numerous similarities and thereforeseveral procedures that are typical and prudent for all fiberglass pipes. Theseprocedures and suggestions should be used in conjunction with the pipe manufac-turer’s instructions. The handling requirements for fiberglass pipe are similar tothose for all types of pipe.

10.2 SHIPPING __________________________________________Preparation for shipping should protect the pipe wall and joining ends from damage,and should be acceptable to the carrier, the manufacturer, and the purchaser.

Ship pipe on flatbed trucks supported on flat timbers or cradles (seeFigure 10-1). A minimum of two supports located at the pipe quarter points is typical.Timber supports should contact only the pipe wall (no joint surfaces). No bells,couplings, or any other joint surface should be permitted to contact the trailer,

AWWA MANUAL M45

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supports, or other pipe. The timber supports must be of sufficient width to avoid pointloading. Chock the pipes to maintain stability and separation. To ensure thatvibrations during transport will not cause abrasion damage, pipes should not beallowed to contact other pipes. Strap the pipe to the vehicle over the support pointsusing pliable straps or rope without deforming the pipe. Bulges, flat areas, or otherabrupt changes in pipe curvature are not permitted. Stack heights to the legal limitsare typically acceptable.

The purchaser should inspect the pipe upon receipt at the jobsite for loss ordamage sustained in transit. Exterior inspection is usually sufficient; however, impactto the pipe exterior can cause interior cracking with little or no visible damage to thepipe exterior. Therefore, interior inspection at the location of exterior scrapes may behelpful when pipe size permits such an inspection. If the load has shifted or exhibitsbroken packaging, inspect each piece both internally and externally. The purchasermay also wish to reinspect the pipe just prior to installation. If any imperfections ordamage are found, contact the supplier for recommendations concerning repair andreplacement. NOTE: Do not use pipe that appears damaged or defective. If in doubt,do not use. If it is necessary to transport pipes at the job site, it is best to use theoriginal shipping dunnage.

10.3 HANDLING _________________________________________Manufacturers’ instructions regarding use of slings, spreader bars, or other handlingdevices should be followed. Lift pipe sections with wide fabric straps, belts, or otherpliable materials. Do not allow the straps to deform the pipe. Avoid the use of steelcables, chains, or other materials that may damage the pipe surface. If cables, chains,or forklifts are used, sufficient care, padding, or protection must be used to preventgouging, cutting, or otherwise damaging the pipe.

Individual pipe sections can usually be lifted with a single sling (seeFigure 10-2) if properly balanced, but two slings as shown in Figure 10-3 (located atthe pipe quarter points) make the pipe easier to control. Do not lift pipe with hooks orrope inserted through the pipe ends.


Figure 10-1 Pipe shipment by truck



Because fiberglass pipe may be damaged by impact, do not drop or impact thepipe, especially the pipe ends. Pipe should never be thrown or dropped to the groundor set on sharp objects. Repair any damage prior to installation.

Bundles. Smaller pipe (24 in. [600 mm] diameter and less) are often unitizedor bundled by the manufacturer as shown in Figures 10-4 and 10-5. Bundles andunitized loads typically must be handled with a pair of slings (never a single sling).Do not lift a nonunitized stack of pipe as a single unit. Nonunitized stacked pipe mustbe unstacked and handled individually.

Nested Pipe. Nesting smaller pipes inside larger pipes is acceptable. Ensurethat the pipes are protected and secured properly to prevent relative motion ordamage during shipment. The pipe manufacturer will provide written instructions forshipping, handling, and denesting of pipe. Never lift nested pipe with a single strap;always use two or more straps as shown in Figure 10-6. Ensure that the lifting straps

Source: Owens Corning Engineered Pipe Systems,Brussels, Belgium.

Figure 10-2 Single sling handling


Figure 10-4 Unitized small diameter bundle

1/4 × L 1/2 × L 1/4 × L


Figure 10-5 Unitized load handling

1/4 × L1/2 × L1/4 × L


Figure 10-3 Double sling handling

SHIPPING, HANDLING, STORAGE, AND REPAIR 141


have the capacity to hold the bundle weight. Denesting is typically accomplished withthree or four fixed cradles that match the outside diameter of the largest pipe in thebundles. Denest beginning with the inside pipe (smallest diameter). The standarddenesting procedure is to insert a padded forklift boom, lift slightly to suspend thepipe, and carefully remove it without touching the other pipe (see Figure 10-7). Whenweight, length, and equipment limitations preclude this method, check with themanufacturer for specific recommendations for removing pipe from the bundle.

10.4 STORAGE __________________________________________Pipe is generally stored on flat timbers to facilitate placement and removal of liftingslings (see Figure 10-8). The support timbers should be of sufficient width to prevent

ControlRope


Figure 10-6 Handling nested pipes


Figure 10-8 Pipe stacking


Figure 10-7 Nesting pipes



point loads. Four-in. wide supports are recommended for large-diameter pipe. Pipeshould be chocked to prevent rolling in high winds. When stacking, timber supportsat the pipe quarter points are best. If available, use the original shipping dunnage forstorage. The maximum stack height is typically 8 ft (2.4 m). Consult the manufac-turer for maximum storage deflection. Bulges, flat areas, or other abrupt changes inpipe curvature are not permitted. Nylon or hemp rope tie-downs are best. Chaintie-downs must be well-padded to prevent damage to the pipe wall.

Rubber ring gaskets should be stored in the shade in the original packaging. Theytypically must be protected from sunlight, solvents, and petroleum-based greases andoils.

When stored directly on the ground, the pipe weight should not be supported bythe bell, coupling, or any other joint surface. The pipe should rest on plane groundand should not rest on rocks, boulders, or other hard debris that may cause a pointload sufficient to gouge, crack, puncture, or otherwise damage the pipe wall. The pipeinterior and all joining surfaces should be kept free of dirt and foreign matter.

Ultraviolet (UV) protection. Check with the pipe manufacturer regardingthe necessity of UV protection when stored outside.

Nested pipe. Store nested pipe only in the original transport packaging. Do notstack nested pipe unless approved by the manufacturer. Transport pipe only in theoriginal transport packaging.

10.5 REPAIR _____________________________________________Typically, damaged pipe can be repaired quickly and easily by qualified personnel ata jobsite. The repair design depends on the wall thickness, wall composition,application, and the type and extent of damage. Do not attempt to repair damaged ordefective pipe without consulting the pipe manufacturer.

Scrapes and gouges on the pipe exterior that are less than 10 percent of the pipewall thickness generally require no repair, while deeper scrapes generally requirerepair. Repair for damage to the inner liner depends on the damage depth. Scratches,scrapes, and abrasion that do not penetrate through the entire liner generally requireno repair. Gouges through the entire liner that penetrate the interior reinforced

Figure 10-9 Patch Figure 10-10 Cutout and replace

SHIPPING, HANDLING, STORAGE, AND REPAIR 143


structural glass require a mat/resin lay-up to restore the original pipe wall thickness.Structural fracture of the pipe wall is evaluated on a case-by-case basis to providerepair sufficient to restore the original pipe strength.

Damaged pipe can either be replaced or repaired. During repair, the pipelinecannot be under pressure and the area to be repaired must be dry throughout theprocedure. Repair techniques include patching small areas (see Figure 10-9), cut-outand replace (see Figure 10-10), repair clamps, hand lay-up, and flexible steelcouplings (see Figure 10-11). Consult the pipe manufacturer to determine which ofthese methods is appropriate.

Consult the pipe manufacturer regarding minor repairs of damaged fittings.Extensively damaged pipe and fittings must be replaced.

Hand lay-up repair. The pipe manufacturer should be contacted for job-spe-cific lay-up instructions. Some manufacturers provide field lay-up kits individuallyprepared for the pipe diameter and pressure rating. Kits include premeasured resin,catalyst, and precut glass mat. The ambient temperature should be between 60°F and100°F (15°C and 38°C), and the repair should be protected from the sun while curingto prevent temperature differentials. Lay-up repairs require clean, controlledconditions and skilled and trained personnel.

Flexible steel couplings can be used for joining pipe sections as well as forrepairs. Steel repair couplings consist of a steel mantle with an interior rubber sleeve.


Figure 10-11 Steel coupling



Glossary

Fiberglass pipe materials, processes, product standards, test methods, and installa-tion practices and procedures may introduce some terms and terminology that arenew to the unfamiliar user. This glossary provides basic definitions of fiberglass pipeterms used in this manual and by the fiberglass pipe industry.

Accelerator See Hardener.

Adapter A fitting used to join two pieces of pipe, or two pipe fittings, thathave different joining systems.

Aggregate Siliceous sand conforming to ASTM C33, except that therequirements for gradation do not apply.

Aliphatic amine curing agent Aliphatic amines are curing agents forepoxy resins. Aliphatic amine cured epoxy resins cure at room temperature,a property that makes them especially suitable for use in adhesives. Somefilament wound pipes use aliphatic amine cured epoxy resins. Theproperties of these pipes depend on the specific amine used in manufacture.

Anhydride curing agents Anhydrides are widely used curing agents forfiberglass reinforced epoxy pipe. The properties of these pipes depend onthe specific anhydride used in manufacture.

Bell and spigot A joining system in which two cylindrical surfaces cometogether to form a seal by adhesive bonding or by compression of anelastomeric gasket. The bell is the female end; the spigot is the male end.

Bisphenol-A One of the major ingredients used to make the mostcommon type of epoxy resin, Bisphenol-A epoxy resin. Also used as anintermediate to produce some polyester resins.

Box The female end of a threaded pipe, or fitting, connection.

Buckling See Collapse.

Burst pressure The ultimate pressure a pipe can resist for a short termbefore failing. Also see Weeping.

Burst strength (hoop stress) The circumferential stress (hoop stress) atburst pressure.

Bushing A fitting used to join two different sizes of pipe by reducing thesize of the female end of the joint.

Catalyst See Hardener.

Centrifugal casting A process used to manufacture tubular goods byapplying resin and reinforcement to the inside of a mold that is rotated andheated, subsequently polymerizing the resin system. The outside diameter(OD) of the finished pipe is determined by the inside diameter (ID) of themold tube. The ID of the finished pipe is determined by the amount ofmaterial introduced into the mold. Other materials may be introduced inthe process during manufacture of the pipe.

145


Collapse Failure caused as the result of application of a uniform forcearound the total circumference of the pipe. The force may be caused by anexternally applied pressure or vacuum inside the pipe. The mode of failureis usually stability related and occurs as flattening of the pipe but can becaused by compressive (shear) failure of the pipe wall.

Collar See Coupling.

Compressive force The force that occurs when opposing loads act on amaterial, thus crushing or attempting to crush it. In pipe, circumferentialcompressive forces may result from external pressure, or longitudinalcompressive forces may result from heating of an end-restrained fiberglasspipe.

Coupling (collar) A short, heavy wall cylindrical fitting used to join twopieces of the same sized pipe in a straight line. The coupling always hasfemale connection ends that can be threaded or that use adhesive bondingor elastomeric seals.

Creep Deformation or strain that occurs over time when a materialexperiences sustained stress. Creep is expressed in in./in./interval of time.Fiberglass pipe is subject to creep at all temperatures when subjected tostress.

Cure The hardening of a thermoset resin system by the action of heatand/or chemical action.

Cure stages Describes the degree to which a thermoset resin has crosslinked. Three stages, in order of increasing crosslinking, include B-stage,gelled, and fully cured.

Curing agent See Hardener.

Cut and mitered fittings Fittings manufactured by cutting, assembling,and bonding pipe sections into a desired configuration. The assembledproduct is then overlayed with resin impregnated roving, mat, or glasscloth to provide required strength.

Cyclic pressure rating The pressure rating obtained as the result ofperforming tests in accordance with ASTM D2992, procedure A. Thismethod rates pipe on the basis of 150 million cycles. This conservativeapproach results in lower pressure ratings for pipes than static testing, butis useful in comparing competitive products.

Design factor (FS) A number equal to or greater than 1.0, which takesinto consideration the variables and degree of safety involved in a design.Test data are divided by the design factor to obtain design allowable values.Reciprocal of service factor. Also called safety factor.

Drift diameter A measure of the effective minimum inside diameter (ID) ofa pipe including ovality and longitudinal warpage over a given length of pipe.

Elastic limit See Proportional limit.

Elastic modulus (modulus of elasticity) The “resistance” of a materialto movement. The slope of the stress–strain curve within the elastic range.

Epoxy resin (thermosetting) A polymer containing two or more three-membered rings, each consisting of one oxygen and two carbon atoms. The



polymer is cured by cross-linking with an amine or anhydride hardener,with or without heat, catalyst, or both.

Fatigue Permanent structural damage in a material subjected to fluctu-ating stress and strain.

Fiberglass pipe A tubular product containing glass-fiber reinforcementsembedded in or surrounded by cured thermosetting resin. The compositestructure may contain aggregate, granular, or platelet fillers, thixotropicagents, and pigments or dyes. Thermoplastic or thermosetting liners orcoatings may be included.

Filament winding A process used to manufacture tubular goods by windingcontinuous glass-fiber roving or roving tape onto the outside of a mandrel orcore pipe liner in a predetermined pattern under controlled tension. Theroving may be saturated with liquid resin or preimpregnated with partiallycured resin. Subsequent polymerization of the resin system may requireapplication of heat. The inside diameter (ID) of the finished pipe is fixed by themandrel diameter or the inner diameter of the core pipe liner. The outsidediameter (OD) of the finished pipe is determined by the amount of materialthat is wound on the mandrel or core pipe liner. Other materials may beintroduced in the process during the manufacture of the pipe.

Fillers Extender materials added to a resin that do not affect the cure ofthe resin, but may influence the physical and mechanical properties of theresin system and the finished product.

Fitting types The classification of fittings by the method of manufacture(i.e., molded, cut and mitered, filament wound).

Gel time The time it takes for a resin system to increase in viscosity soflow will not occur.

Glass fabric A bi-directional fabric reinforcing material made by theweaving of glass-fiber yarn.

Glass fibers A commercial grade of glass filaments with binder and sizingthat are compatible with the impregnating resin.

Hand lay-up Any of a number of methods for forming resin and fiberglassinto finished pipe products by manual procedures. These proceduresinclude overwrap techniques, contact molding, hand molding, and others.Complex shapes can be fabricated.

Hardener (accelerator, catalyst, curing agent, promoter) Any of anumber of chemicals added to the resin, individually or in combination,that speed up the curing process or cause hardening to occur.

Hoop stress Circumferential stress. See also Burst strength.

Hydrostatic Design Basis (HDB) The long-term hydrostatic hoop strengthof a specific fiberglass pipe material for water service as determined by testsand detailed evaluation procedures in accordance with ASTM D2992.

Isopolyester Unsaturated polyester based on isophthalic acid.

Integral joint A joint configuration in which the connection is an integralpart of the pipe. A length of pipe with integral joints will have one male endand one female end.

GLOSSARY 147


Joining (connecting) systems Any of a variety of methods for connect-ing two separate components of a piping system together. Included are belland spigot, threaded, coupling, and mechanical devices.

Joint A term sometimes used to describe an individual length of pipe aswell as the actual joining mechanism (i.e., adhesive bonded bell and spigot,threaded, gasketed bell and spigot, gasketed coupling, etc.).

Liner A filled or unfilled thermoplastic or thermosetting resin layer,nonreinforced or reinforced, forming the interior surface of the pipe.

Matrix The resin material used to bind reinforcements and fillerstogether. This resin may be epoxy or polyester and dictates to a largeextent the temperature and chemical performance for a pipe or fitting.

Minimum bending radius The allowable deflection of the center-line ofa pipe before damage occurs. The radius refers to an imaginary circle ofwhich the pipe length would be an arc.

Mitered fittings See Cut and mitered fittings.

Modulus of elasticity See Elastic modulus.

Molded fittings Pipe fittings formed by compressing resin, chopped fiber,and other ingredients in a mold under heat and pressure.

Pin The male end of a pipe or fitting that matches with the female end ofanother pipe or fitting.

Pipe stiffness A measure of the force required to deflect the diameter ofa pipe ring a unit amount.

Poisson’s effect (ratio) The property of a material that causes a change in itsdimensions due to a force applied perpendicular to the plane of the dimensionchange. Expressed as the ratio of lateral strain to load direction strain.

Polyester resin (thermosetting) An ethylenic unsaturated polymer withtwo or more ester groups, dissolved in a reactive diluent with vinylunsaturation. The polymer is cured by cross linking by means of afree-radical-initiated curing mechanism, such as peroxide catalyst and heat.

Any of a large family of resins that are normally cured by crosslinking withstyrene. The physical and chemical properties of polyester resins varygreatly. Some have excellent chemical and physical properties while othersdo not. Vinyl esters are a specific type of polyester resin. Polyester resinswith properties suitable for use in the manufacture of fiberglass pipeinclude orthophthalic, isophthalic, Bisphenol-A fumarate, and chlorhendicanhydride acid polyesters. Each type of resin has particular strengths andweaknesses for a given piping application.

Pressure class The maximum sustained pressure for which the pipe is designed.

Pressure rating The maximum long-term operating pressure a manufac-turer recommends for a given product. Also referred to as design pressure.

Promoter See Hardener.

Proportional (elastic) limit The greatest stress a material can sustainfor a short time without causing permanent deformation. It is defined by



the point at which the stress–strain curve deviates from linearity. Forcomposite materials, this point is called the “apparent elastic limit” since itis an arbitrary approximation on a nonlinear stress–strain curve. SeeStress–strain diagram.

Reducer A pipe fitting used to join two different sized pieces of pipe. Withthe same centerline in both pipes the reducer is concentric; if centerlinesare offset it is eccentric.

Reinforced plastic-mortar pipe (RPMP) A fiberglass pipe withaggregate.

Reinforced thermosetting-resin pipe (RTRP) A fiberglass pipewithout aggregate.

Reinforcement Glass fibers used to provide strength and stiffness to acomposite material. The form of reinforcement plays a major roll indetermining the properties of a composite. The fiber diameter and the typeof sizing used are also factors. Terms relating to the physical form of thereinforcement include:

Chopped fiber—Continuous fibers cut into short (0.125 in. to 2.0 in.[3.2 mm to 50 mm]) lengths.

Filament—A single fiber of glass (e.g., a monofilament).

Mats—A fibrous material consisting of random-oriented, chopped, orswirled filaments, loosely held together with a binder.

Milled fibers—Glass fibers, ground or milled into short (0.032 in. to0.125 in. [0.81 mm to 3.2 mm]) lengths.

Roving—A collection of parallel glass strands or filaments coated with afinish or coupling agent to improve compatibility with resins, gatheredwithout mechanical twist. Roving may be processed in a continuous orchopped form.

Yarn—Glass fiber filaments twisted together to form textile type fibers.

Yield—The number of yards of material made from one pound of product.

Resin Any class of solid or pseudosolid organic materials, often of highmolecular weight, with no definite melting point. In the broad sense, theterm is used to designate any polymer that is a basic material for plastics.

Service factor A number less than or equal to 1.0 that takes intoconsideration the variables and degree of safety involved in a design. Theservice design factor is multiplied by test values to obtain designallowables. Reciprocal of Design factor.

Static pressure rating The recommended constant pressure, at which pipecan be operated continuously for long periods without failure. Determined byconducting tests in accordance with ASTM D2992, procedure B.

Stiffness class The nominal stiffness of a specified pipe.

Strain Dimensional change per unit of length resultant from applied forceor load. Measured in in. per in. (mm/mm).

Stress The force per unit of cross-sectional area. Measured in psi (kPa).

GLOSSARY 149


Stress–strain diagram A graphic presentation of unit stress versus thecorresponding unit strain. As the load increases, elongation or deformationof the material also increases.

Support spacing The recommended maximum distance between pipesupports to prevent excessive pipe deformation (bending).

Surface layer A filled or unfilled resin layer, nonreinforced or reinforced,applied to the exterior surface of the pipe structural wall.

Surfacing mat A thin mat of fine fibers used primarily to produce asmooth surface on a reinforced plastic. Also called surfacing veil.

Surge allowance That portion of the surge pressure that can beaccommodated without changing pipe pressure class. The surge allowanceis expected to accommodate pressure surges usually encountered in typicalwater distribution systems.

Surge pressure A transient pressure increase greater than workingpressure, sometimes called water hammer, that is anticipated in a systemas a result of a change in the velocity of the water, such as when valves areoperated or when pumps are started or stopped.

Tape A unidirectional glass-fiber reinforcement consisting of rovingsknitted or woven into ribbon form.

Tensile force A force applied to a body tending to pull the material apart.

Thermal conductivity The rate at which a material transmits heat froman area of high temperature to an area of lower temperature. Fiberglasspipe has low thermal conductivity.

Thermal expansion The increase in dimensions of a material resultingfrom the application of heat. Thermal expansion is positive as temperatureincreases and negative as temperature decreases.

Thermoplastic resin A plastic that can be repeatedly softened byheating and hardened by cooling, and that, in the softened state, can befused or shaped by flow.

Thermoset A polymeric resin cured by heat or chemical additives. Oncecured, a thermoset resin becomes essentially infusible (cannot be remelted)and insoluble. Thermosetting resins used in pipe generally incorporatereinforcements. Typical thermosets include:

Vinyl esters Novolac or Epoxy Novolac Bisphenol-A methacrylates Bisphenol-F methacrylates Unsaturated Polyesters

Orthophthalic polyester Isophthalic polyester

Bisphenol-A fumarate polyester HET acid polyester

Epoxies Amine cured

Anhydride cured Aliphatic polyanhydrides Cycloaliphatic anhydrides

Aromatic anhydrides



Thrust forces Commonly used to describe the forces resulting fromchanges in direction of a moving column of fluid. Also used to describe theaxial or longitudinal end loads at fittings, valves, etc., resulting fromhydraulic pressure or thermal expansion.

Torque Used to quantify a twisting force (torsion) in pipe. Torque is measuredas a force times the distance from the force to the axis of rotation. Torque isexpressed in ft-pounds (ft-lb) or in.-pounds (in.-lb) (Newton meters [N-m]).

Ultimate pressure The ultimate pressure a pipe can resist for a shorttime before failing. This pressure is typically determined by the ASTMD1599 test. May also be referred to as ultimate burst pressure. For somefiberglass pipes, when pressured to their ultimate pressure, the failuremode may be by leakage or weeping through the pipe wall rather thanfracture of the pipe wall.

Vinyl ester A premium resin system with excellent corrosion resistance.

Weeping Leakage of minute amounts of fluid through the pipe wall.

Working pressure The maximum anticipated, long-term operating pres-sure of the water system resulting from normal system operation.

Woven roving A glass-fiber fabric reinforcing material made by theweaving of glass-fiber roving.

GLOSSARY 151


Index

NOTE: f. indicates a figure; t. indicates a table.

Aboveground pipe design, 103allowable tensile or compressive loads,

122anchor rules, 114-116anchors, 108, 109, 114-116, 117, 117f.bending, 120bending loads, 122-123buckling scaling constant, 123compressive loads, 122compressive scaling constant, 123cradles, 115, 116f.design stresses, 122directional changes, 113-114, 114f.expansion joints, 110-111, 111f.expansion loops, 112-113external pressure, 123fatigue resistance (cyclic), 105, 105f.fatigue resistance (static), 105, 106f.guide rules, 114-116guides, 109-110, 114-116, 117f.heat tracing, 121-122hoop strain calculations, 106hoop tensile stress calculations, 106internal pressure rating, 105-106modulus of elasticity, 122physical properties, 103, 104t.Poisson’s ratio, 123service design factors, 105six rules for supports, anchors, and

guides, 114-116spacing design, 109-110support rules, 114-116supporting valves and other heavy

equipment, 115, 116f.supports, 115, 115t., 117-120, 118f., tensile loads, 122test methods, 103, 104t.thermal conductivity, 120-121thermal end loads, 108-109thermal expansion and contraction, 107thermal expansion design, 107-114Type I supports, 117-119Type II supports, 119Type III supports, 119Type IV supports, 120vacuum pressure, 123vertical runs, 116, 116f.

American National Standards Institute, 2American Petroleum Institute, 2American Society for Testing and

Materials, 2American Society of Mechanical Engineers,

2Anchors, 108, 109, 117, 117f.

rules, 114, 116

ANSI. See American National StandardsInstitute

API. See American Petroleum InstituteASME. See American Society of

Mechanical EngineersASTM. See American Society for Testing

and Materials, 2

Backfill, 84-86final, 76initial, 76minimum cover, 86with small-horizontal-deflection thrust

restraint, 96-98, 97f.Bedding, 75Bending design factor, 42Buckling

calculations, 52-54theory, 52

Buried pipe. See Buried pipe design,Thrust restraints, Undergroundinstallation

Buried pipe design, 35. See alsoAboveground pipe design,Underground installation

axial loads, 54bending design factor, 42buckling, 52-54combined loading, 51-52conditions, 36-38deflection, 42-51example 1 (stress basis), 54-61, 55t.example 2 (strain basis), 55t., 61-66example 3 (strain basis), 55t., 66-71installation parameters, 38-39internal pressure, 39-41pipe properties, 38procedure, 39ring-bending, 41-42ring-bending strain, 42shape factor, 41-42, 42t.special considerations, 54terminology, 35-36variables, 36f.-37f.

Centrifugal casting, 18, 20f.chopped glass reinforcement method, 18,

19f.preformed glass reinforcement sleeve

method, 18, 19f.Chemical resistance testing, 5Combined loading, 51-52Compactibility, 75Compressive property

test methods, 4Cross-section, 75, 75f.

153


Darcy-Weisbach equation, 25-27Deflection, 42-43, 75

bedding coefficient, 44calculations, 43lag factor, 44live loads, 44-46, 45f. modulus of soil reaction, 46-51, monitoring, 87-88pipe stiffness, 46prediction, 43vertical soil load, 44

Design. See Aboveground pipe design,Buried pipe design

Design factor, 36Diameter

equations, 22Differential settlement, 83, 84f., 85f., 87

E′. See Modulus of soil reactionEconomic analysis. See Energy

consumption calculationsEmbedment materials, 77. See also Pipe

installation, Soil, Undergroundinstallation

categories with recommendations, 79t.consolidation using water, 86maximum particle size, 78migration, 78-80moisture content, 78soil stiffness categories, 77-78, 78t.

Energy consumption calculations, 29-31Engineer, 76

Factory Mutual Research, 2, 5Fiberglass

fillers, 10glass fiber reinforcements, 8-9inhibitors, 10other components, 10pigments, 10promoters and accelerators, 10resins, 8, 9-10

Fiberglass pipe. See also Pipe installationabrasion resistance, 11alternate names, 1applications, 2approvals, 5buried pipe design, 35-71centrifugal casting, 18-20characteristics, 7-8chemical resistance, 11chemical resistance testing, 5compressive property test methods, 4corrosion resistance, 7diameter equations, 22diameters, 2dimensional stability, 7-8dimensions, 4electrical properties, 7energy consumption calculations, 29-31external pressure testing, 5

filament winding, 15-18finishing ovens, 17, 18f.first introduction, 1flame retardants, 11-12handling, 140-142, 141f., 142f.head loss, 23-29history, 1-2hydraulics, 21-34installation, 4joining systems, 125-138lightness of weight, 7long-term internal pressure strength

testing, 4maintenance costs, 8manufacturing, 15-20materials, 1, 7- 10mechanical properties, 12, 13f.physical properties, 11-12pipe stiffness testing, 5piping codes, 5preliminary pipe sizing, 21-22pressures, 2product listings, 5recommended practices, 4repair, 143-144, 143f., 144f.resins, 1, 9-10resistance to biological attack, 12roughness coefficient, 23, 24shipping, 139-140, 140f.specifications, 2-4standards, 2-5storage, 142-143, 142f.strength to weight ratio, 7temperature resistance, 11tensile property test methods, 4test methods, 4-5and tuberculation, 12underground installation, 73-88velocity equations, 22water hammer, 31-34weathering resistance, 12weight, 7

Filament winding, 15continuous methods, 17, 17f., 18f.multiple mandrel method, 17process, 15, 16f.reciprocal method, 15ring and oscillating mandrel method, 18

Final backfill, 76Finishing ovens, 17, 18f.Fittings

head loss in, 27-29loss coefficients (K factors), 27-28, 28t.

FMR. See Factory Mutual ResearchFoundation, 76

Geotextile, 76Glass fiber reinforcements, 8

arrangements (fiber orientations), 9bidirectional, 9continuous roving form, 8forms, 8-9



multidirectional (isotropic), 9reinforcing mats, 9surface veils, 9types, 8unidirectional, 9woven roving form, 9

Guides, 109-110, 116, 117f.rules, 114, 116

Handling, 140-142bundles (unitized loads), 141, 141f.nested pipes, 141-142, 142f.

Haunching, 75f., 76, 84, 85f.Hazen-Williams equation, 23-24, 23f.HDB. See Hydrostatic design basisHead loss, 23, 29, 37-38

conversion to pressure drop, 24-25Darcy-Weisbach equation, 25-27in fittings, 27-29Hazen-Williams equation, 23-24, 23f.loss coefficients (K factors) for fittings,

27-28, 28t.Manning equation, 25Moody diagram, 26f., 27Reynolds number, 25, 27

Hydrostatic design basis, 36, 40Hydrostatic thrust, 91-92, 92f.

In situ soils, 76, 77Initial backfill, 76Internal shock. See Water hammer

Joining systemsadhesive-bonded joints, 126bell and spigot joints, 125, 126, 126f.,

127-129, 127f., 128f., 129f.bonded joints, 133compression molding, 134-135, 134f.contact molding, 138coupling, 129, 130f.fiberglass couplings, 125filament winding, 135fittings and specials, 134-138flanged joints, 134gasket sealed joints, 127-129, 129f.gaskets, 126heating and heating devices, 132, 133layout and preparation, 132machining equipment, 132mechanical coupling joints, 125mechanical joints, 129-131, 131f., 132f.mitered fittings, 135-136, 135f., 136f.,

137f.pipe cutting equipment, 132power drive adapters, 132reinforced-overlay joints, 126-127, 128f.restrained gasketed joints, 129, 130f.restrained pipe joints, 125-126safety and protective measures, 132, 134service line connections, 138threaded joints, 133-134tools and equipment, 132

unrestrained pipe joints, 125wrenches, 132

Mandrels, 15, 16f.Manning equation, 25Manufactured aggregates, 76Maximum standard Proctor density, 76Modulus of soil reaction, 46-51

values for native soil at pipe zoneelevation, 51t.

values for pipe zone embedment, 49t.-50t.Moody diagram, 26f., 27

Native soil, 76NSF International, 2, 5

Occupational Safety and HealthAdministration, 132

Open-graded aggregate, 76Optimum moisture content, 76

Pipe design. See Aboveground pipe design,Buried pipe design

Pipe installation. See also Embedmentmaterials, Soil, Undergroundinstallation

adhesive bonded and wrapped joints, 84adjacent systems, 85f., 87backfill, 84-86bedding material and support, 82-83, 82f.caps and plugs, 87compaction, 84-86, 85f.compaction of soils with few fines, 85compaction of soils with significant

fines, 86compaction of soils with some fines, 85connections and appurtenant

structures, 87connections to manholes, 87consolidation of embedment using

water, 86determination of in-place soil density, 86differential settlement, 83, 84f., 85f., 87elastomeric seal (gasketed) joints, 83-84exposing pipe for service line

connections, 87foundation, 82jointing, 83localized loadings, 83, 84f., 85f.location and alignment, 83minimum cover, 86and overexcavation, 83placing and joining, 83-84and rock or unyielding materials, 83and sloughing, 83thrust blocks, 87trench preparation, 82-83and unstable trench bottom, 83vertical risers, 87

Pipe stiffness testing, 5Pipe zone embedment, 76. See also

Embedment materials

INDEX 155


Power cost calculations. See Energyconsumption calculations

Pressure. See also Head loss, Workingpressure, Pressure class

aboveground external, 123aboveground internal rating, 105-106aboveground vacuum, 123external pressure testing, 5internal, 39-41long-term internal pressure strength

testing, 4Pressure class, 35, 39-40Pressure drop. See Head lossPressure loss. See Head lossPressure surge. See Water hammerProcessed aggregates, 76

Recommended practices, 4Relative density, 76Repair, 143-144

clamps, 144cut-out and replace, 143f., 144hand lay-up, 144patching, 143f., 144steel coupling, 144, 144f.

Resins, 9-10catalysts, 9-10epoxy, 10polyester, 9-10

Ring-bending, 41-42long-term strain, 42

Roughness coefficient, 23, 24

Shape factor, 41-42, 42t.Soil

categories with recommendations, 79t.classification chart, 47t.compaction, 84-86, 85f.compaction of soils with few fines, 85compaction of soils with significant fines,

86compaction of soils with some fines, 85consolidation using water, 86determination of in-place density, 86horizontal bearing strengths, 93, 94t.maximum particle size, 78migration, 78-80minimum density, 86modulus of soil reaction, 46-51moisture content, 78stiffness categories, 77-78, 78t.support combining factor, 48, 48t.

Soil stiffness, 76categories, 77-78, 78t.

Specifications, 2-4military, 3-4societies, 2

Split installation, 76Standards, 2-5

chemical resistance testing, 5compressive property test methods, 4external pressure testing, 5

long-term internal pressure strengthtesting, 4

pipe stiffness testing, 5recommended practices, 4societies, 2tensile property test methods, 4test methods, 4-5underground installation, 74-75

Storage, 142-143of nested pipe, 143stacking, 142-143, 142f.ultraviolet protection, 143

Strain basis design examples, 55t., 61-71Stress basis design examples, 54-61, 55t.Supports

aboveground, 115, 115t., 117-120, 118f., rules, 114-116trench, 81-82Type I, 117-119Type II, 119Type III, 119 Type IV, 120

Surge allowance, 36, 41Surge pressure, 36, 38, 40-41

Talbot equation, 32Tensile property

test methods, 4Terminology, 75-76Test methods, 4-5Thrust blocks, 87, 93-95, 93f.

and adjacent excavation, 95calculating size, 93configurations, 93f., 94, 95f.proper construction, 94

Thust restraintsdead weight resistance, 101horizontal bends and bulkheads, 100horizontal soil-bearing strengths, 93, 94t.hydrostatic thrust, 91-92, 92f.joints with small deflections, 95-99small horizontal deflections, 95-98, 96f.,

97f.small vertical deflections with joints free

to rotate, 98-99, 98f.thrust blocks, 93-95, 93f.thrust resistance, 92tied joints, 99-102, 99f.transmission of thrust force through

pipe, 102unbalanced thrust forces, 91vertical (uplift) bends, 101-102, 101f.

Transient pressures. See Water hammerTrench excavation and preparation, 80

bedding material and support, 82-83, 82f.differential settlement, 83, 84f., 85f., 87foundation, 82groundwater, 80-81localized loadings, 83, 84f.minimum trench width, 81movable supports, 81overexcavation, 83



removal of supports, 81-82rock and unyielding materials, 83running water, 81sloughing, 83support of trench walls, 81supports left in place, 81trench bottom, 82, 83unstable trench bottom, 83water control materials, 81water control, 80

UL. See Underwriters LaboratoriesUnderground installation, 73-74. See also

Embedment materials, Pipeinstallation, Soil

backfill, 84-86bedding, 75compactibility, 75contract document recommendations, 88cross-section, 75, 75f.deflection, 75embedment materials, 77-80engineer, 76field monitoring, 87-88final backfill, 76foundation, 76geotextile, 76haunching, 75f., 76, 84, 85f.

in situ soil, 76initial backfill, 76manufactured aggregates, 76maximum standard Proctor density, 76native soil, 76open-graded aggregate, 76optimum moisture content, 76pipe installation, 82-87pipe zone embedment, 76, 77-80placing and joining pipe, 83-84processed aggregates, 76related standards, 73, 74-75relative density, 76soil stiffness, 76soil stiffness categories, 77-78, 78t.split installation, 76terminology, 75-76trench excavation, 80-82

Underwriters Laboratories, 2, 5U.S. Department of Transportation, 5

Velocityequations, 22

Water hammer, 31-32calculation of, 32-34Talbot equation, 32

INDEX 157


AWWA Manuals

M1, Water Rates, Fourth Edition, 1991,#30001PA

M2, Automation and Instrumentation,Second Edition, 1983, #30002PA

M3, Safety Practices for Water Utilities,Fifth Edition, 1990, #30003PA

M4, Water Fluoridation Principles andPractices, Fourth Edition, 1995,#30004PA

M5, Water Utility Management Practices,First Edition, 1980, #30005PA

M6, Water Meters—Selection,Installation, Testing, andMaintenance, First Edition, 1986,#30006PA

M7, Problem Organisms in Water:Identification and Treatment, SecondEdition, 1995, #30007PA

M9, Concrete Pressure Pipe, SecondEdition, 1995, #30009PA

M11, Steel Pipe—A Guide for Design andInstallation, Fourth Edition, 1989,#30011PA

M12, Simplified Procedures for WaterExamination, Second Edition, 1977,#30012PA

M14, Recommended Practice for BackflowPrevention and Cross-ConnectionControl, Second Edition, 1990,#30014PA

M17, Installation, Field Testing, andMaintenance of Fire Hydrants, ThirdEdition, 1989, #30017PA

M19, Emergency Planning for WaterUtility Management, Third Edition,1984, #30019PA

M20, Water Chlorination Principles andPractices, First Edition, 1973,#30020PA

M21, Groundwater, Second Edition, 1989,#30021PA

M22, Sizing Water Service Lines andMeters, First Edition, 1975,#30022PA

M23, PVC Pipe—Design and Installation,First Edition, 1980, #30023PA

M24, Dual Water Systems, Second Edition,1994, #30024PA

M25, Flexible-Membrane Covers andLinings for Potable-Water Reservoirs,First Edition, 1996, #30025PA

M26, Water Rates and Related Charges,First Edition, 1986; Second Edition1996, #30026PA

M27, External Corrosion—Introduction toChemistry and Control, FirstEdition, 1987, #30027PA

M28, Cleaning and Lining Water Mains,First Edition, 1987, #30028PA

M29, Water Utility Capital Financing,First Edition, 1988, #30029PA

M30, Precoat Filtration, Second Edition,1995, #30030PA

M31, Distribution System Requirementsfor Fire Protection, Second Edition,1992, #30031PA

M32, Distribution Network Analysis forWater Utilities, First Edition, 1989,#30032PA

M33, Flowmeters in Water Supply, FirstEdition, 1989, #30033PA

M34, Alternative Rates, First Edition,1992, #30034PA

M35, Revenue Requirements, First Edition,1990, #30035PA

M36, Water Audits and Leak Detection,First Edition, 1990, #30036PA

M37, Operational Control of Coagulationand Filtration Processes, FirstEdition, 1992, #30037PA

M38, Electrodialysis and ElectrodialysisReversal, First Edition, 1995,#30038PA

M41, Ductile-Iron Pipe and Fittings, FirstEdition, 1996, #30041PA

M44, Valve Installation and Maintenance,First Edition, 1996, #30044PA

M47, Construction Contract Administration,First Edition, 1996, #30047PA

To order any of these manuals or other AWWA publications, call the Bookstore toll-free at 1 (800) 926-7337.

159


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