Manual de Diseño HDPE.

Polyethylene Pipin gSystems Manual

Innovative Supplier of Quality Piping Systems.

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TABLE OF CONTENTS

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TABLE OF CONTENTS ......................................................................................................I-IILIST OF TABLES ................................................................................................................IIILIST OF FIGURES ..............................................................................................................IVINTRODUCTION .................................................................................................................1

Driscopipe Piping Systems .....................................................................................2Characteristics of HDPE Pipe .................................................................................2Cautions ..................................................................................................................6Driscopipe Materials ...............................................................................................8Joining Polyethylene Pipe.........................................................................................9Design Considerations .............................................................................................10Installation Considerations ......................................................................................11Other Considerations ..............................................................................................12Contingency and Risk..............................................................................................13

DRISCOPIPEfi SYSTEMS DESIGN......................................................................................14System Pressure Requirements .............................................................................14

Dimension Ratio .........................................................................................14Design Pressure Ratings ............................................................................14Positive Pressure Pipelines ........................................................................15Water Hammer/ Pressure Surge ................................................................16Longitudinal Stress From Internal Pressure ...............................................17Fluid Flow ...................................................................................................17Initial Flow Estimates .................................................................................18Pressurized Flow .......................................................................................18Fitting Pressure Drop .................................................................................20Pressure Loss For Viscous Fluids .............................................................20Gravity Flow ................................................................................................21Vacuum or Suction Pipelines......................................................................25Sliplining Existing Lines .............................................................................27Gas Flow ...................................................................................................28

Thermal Considerations ..........................................................................................29Working Pressure Ratings (WPR).............................................................29Thermal Conductivity .................................................................................29Thermal Expansion and Contraction .........................................................29Thermal Stress Relaxation .........................................................................30 30Thermal Considerations in Supported Pipelines ........................................30Thermal Considerations in Overland Pipelines ..........................................30Lateral Deflection Due to Thermal Movement ............................................30Thermal Considerations in Buried Pipelines................................................31Thermal Considerations in Marine Pipelines ..............................................32Transition Connections ...............................................................................32

Burial Design ...........................................................................................................35Buried Pipelines...........................................................................................35Burial Design Considerations ......................................................................35Limits on Buried Pipe Due to External Soil Pressure ...................................35Calculation of Total Soil Pressure by Components .....................................36Burial Design Guidelines .............................................................................42

DRISCOPIPEfi SYSTEMS INSTALLATION .........................................................................47Supported or Suspended Pipelines............................................................................47

Pipe Support Spacing ..................................................................................47Overland Pipelines ....................................................................................................49

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Hot Climates ...............................................................................................49 5 5Cold Climates...............................................................................................50 5

Marine Pipelines .......................................................................................................50Critical Collapse Pressure ..........................................................................50Anchor Weights .........................................................................................50Anchor Spacing...........................................................................................50Installation of Marine Pipelines ..................................................................52

Water Surface Pipelines..........................................................................................53Marsh Pipelines ......................................................................................................53Sliplined Pipelines ...................................................................................................54Buried Pipelines ......................................................................................................55

Trenching and Bed Preparation .................................................................55Pipe Laying .................................................................................................57Fitting Installation .......................................................................................58

Pressure Testing Driscopipe Systems ....................................................................59Repair Techniques ..................................................................................................60

SHIPPING, HANDLING, & UNLOADING ............................................................................62Shipping ..................................................................................................................62Handling ..................................................................................................................62Unloading ................................................................................................................63Storage ....................................................................................................................64

INDEX ..................................................................................................................................65

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LIST OF TABLESPage

Table 1: Driscopipefi HDPE Chemical Resistance Data........................................................... 3, 4Table 2: Minimum Allowable Bend Radius @ 73.4 F....................................................................5Table 3: Identification by Cell Classification- ASTM D 3350.........................................................8Table 4: HDB Values for Medium and High Density Polyethylene............................................. 15Table 5: Working Pressure Ratings for Driscopipe PE 3408 Pipe at 23 C...................................1519Table 6: C Values for Hazen and Williams Formula ..............................................................19Table 7: Equivalent Lengths for Estimating Pressure Drop Through Fittings................................20Table 8: Changes in Velocity and Flow Capacity as a Function of Full Flow.............................. 22Table 9: Differential Pressure (Vacuum or External Fluid) Capability for

Unsupported Pipe @ 73.4 F............................................................................................26Table 10: Multipliers for Temperature Rerating...............................................................................26Table 11: Driscopipefi PE 3408 Pipe - Pressure rating (psi) vs. Temperature ( F)........................ 29Table 12: Instantaneous Modulus of Elasticity (psi) vs. Temperature ( F)......................................30Table 13: Value of E Based on Soil Type (ASTM D 2321) and Degree of Compaction . 36Table 14: Determining Soil Pressure from a Static Load . . 40Table 15: Allowable Ring Deflection of Driscopipefi Polyethylene Pipe Based upon DR 45Table 16: Allowance for Expansion under Test Pressure . 60Table 17: Standard Packaging for Driscopipefi Industrial Pipe . 62Table 18: Allowable Stacking Heights for Driscopipefi HDPE Pipe . . 64

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LIST OF FIGURESPage

Figure 1: Examples of Critical Flow for Viscous Slurries and Slurry Tailings.................................24Figure 2: Ring Deflection of Polyethylene Pipe.......................................................................... 27Figure 3: Lateral Deflection Due to Thermal Movement in Overland Pipelines....................... 31Figure 4: Unit Underground Soil Pressure Exerted by 1000 lb Load..............................................38Figure 5: H20 Highway Loading......................................................................................................41Figure 6: Cooper E-80 Live Loading................................................................................................42 42Figure 7: Plot of Vertical Stress-Strain Data for Typical Trench Backfill

(Except Clay) from Actual Tests......................................................................................44Figure 8: Calculating Ring Deflection........................................................................................ 45Figure 9: Pipe Support Spacing for DR32.5....................................................................................48Figure 10: Pipe Support Spacing for DR26.......................................................................................48Figure 11: Pipe Support Spacing for DR17.......................................................................................48Figure 12: Pipe Support Spacing for DR11.......................................................................................48Figure 13: Pipe Support Spacing for DR9................................................................................... 48Figure 14: Maximum Span Between Concrete Weights for Underwater Driscopipefi Pipelines.......51Figure 15: Anchor Weight Design.....................................................................................................52Figure 16: Suggestions for Transitioning Polyethylene Pipe to a Concrete Manhole................ ......54-55Figure 17: Examples of Concrete Thrust Blocks and Encasements.................................................56Figure 18: Trench Construction and Terminology.............................................................................57Figure 19: Concrete Supports for a Flanged Connection..................................................................58Figure 20: Using Flanged Connections to Repair a Damaged Pipe Section.....................................61

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POLYETHYLENE PIPINGSYSTEMS MANUAL

INTRODUCTIONThe plastics industry is more than 100 years old, but polyethylene was not invented until the 1930’s.Early polyethylenes were low density and were used primarily for cable coatings. Today's modernpolyethylene piping systems began with Phillips’ discovery of high density polyethylene in the early1950’s.

Today, Phillips Petroleum Company is one of the world's largest producers of polyolefin plastics.Phillips technology is used to manufacture much of the world's high density polyethylene. From theraw materials at the well head to the finished piping product, Phillips Petroleum Company and PhillipsDriscopipe develop and test high density polyethylene compounds and piping components. Thespecialized polyethylene resins used in Driscopipe® products are a result of this leadership andtechnical expertise.

Driscopipe piping systems, produced with Marlex® resins, have been installed world-wide. Tens ofthousands of miles of this pipe are in service in hundreds of different natural gas, industrial, andmunicipal applications.

This manual provides accurate and reliable information to the best of Phillips Driscopipe’s knowledge,but our suggestions and recommendations cannot be guaranteed because the conditions of use arebeyond our control. Each project has its own set of variables and conditions. Interpretation of thesevariables is important. The user must apply proper engineering judgement when designing andinstalling polyethylene piping systems. Phillips Petroleum Company and Phillips Driscopipe assumeno responsibility for the information presented herein and hereby expressly disclaim all liability relatingto the use of this information.

The information presented in this manual is based upon a PE3408 high density polyethylene resin witha cell classification of 345444C per ASTM D3350.

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DRISCOPIPE® PIPING SYSTEMSPhillips Driscopipe offers a complete line of pipe, fittings, and accessories as well as technical andinstallation support. Driscopipe systems include the following:

• Pipe and fittings in many sizes and design pressure ratings.• Custom fabrication of special components.• ISO 9001 Certification.• Technical personnel for consultation on design and installation of your system.• Product research, development, and testing.• Strategically located plants throughout the United States and abroad.• Qualified distributors.

ADVANTAGES Compared to traditional piping materials, Driscopipe HDPE pipe systems may offercost savings in installation, labor, and equipment. Considering the potential for reduced maintenancecosts and extended service life in many pipeline applications, Driscopipe polyethylene pipe is verycompetitive.

APPLICATIONS Typical applications include chemicals, acid and caustic solutions, corrosive waste,sewage, drainage, mine tailings, sludge, process and potable water, saltwater, corrosive gases,slurries, mud, crude oil, fuel gases, and many others. Phillips Driscopipe manufactures products tothe requirements of NSF and the American Water Works Association for use in potable watersystems, ASTM D2513 for natural gas distribution systems, and Factory Mutual for installation ofunderground fire protection systems.

PIPE Phillips Driscopipe produces high density and medium density polyethylene pipe and tubing insizes from ¾” through 54” in iron pipe sizes (IPS). Ductile iron pipe sizes (DIPS) are available through24” for the potable water market. Copper tube sizes (CTS) are available for natural gas distributionand water service tubing.

FITTINGS Molded fittings are available in sizes through 12" IPS. Fittings fabricated from pipe areavailable in various pressure ranges in sizes 1/2" through 54". Standard fabricated fittings and specialitems or assemblies are available on special order.

CHARACTERISTICS OF HDPE PIPE

ABRASION RESISTANCE In tests conducted by Williams Brothers Engineering Company (Tulsa,Oklahoma), Driscopipe high density polyethylene pipe was compared with X-52 grade steel pipe.Both piping systems were wear tested and compared using an iron ore-water slurry. The magnetitehad a specific gravity of five (five times the weight of water) and a coarse particle size. With a slurryvelocity of 13.5 feet per second, the Driscopipe system outperformed the X-52 steel pipe system 4 to1. With a velocity of 17 feet per second, the performance ratio was 3 to 1. These tests, undercontrolled conditions, demonstrate that polyethylene pipe is superior to steel in slurry handlingapplications. Driscopipe products have demonstrated outstanding performance in handling minetailings, fly ash, mud and rocks from dredging applications, and other abrasive materials.

CHEMICAL RESISTANCE Driscopipe HDPE pipe is suitable for many chemical solutions.Naturally occurring chemicals in the soil will not degrade the pipe. It is not an electrical conductor anddoes not rot, rust, or corrode by electrolytic action. It does not support the growth of algae, bacteria,or fungi and is resistant to marine biological attack. Gaseous hydrocarbons have no effect on

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expected service life. Liquid hydrocarbons will permeate the wall and reduce hydrostatic strength.When the hydrocarbon evaporates, the pipe will regain its original physical properties.

Some chemicals will affect polyethylene pipe. Chemical attack may be accompanied by anycombination of the following: swelling, discoloration, brittleness, or loss of strength. Laboratory testsusing non-stressed specimens under static conditions were used to develop the following data. Theratings shown are based primarily on chemical attack, solvent swelling, and changes in physicalproperties.

TABLE 1: DRISCOPIPE ® HDPE CHEMICAL RESISTANCE DATA

Legend: “S” -- Satisfactory “O” -- Some Attack “U” -- Unsatisfactory “NA” -- No Data Available

70OF 140OFAcrylic Emulsions S SAluminum Chloride Dilute S SAluminum Chloride Concentrated S SAluminum Fluoride Concentrated S SAluminum Sulfate Concentrated S S

Ammonia 100% Dry Gas S SAmmonium Carbonate S SAmmonium Chloride Saturated S SAmmonium Floride 20% S SAmmonium Metaphosphate Saturated S S

Ammonium Persulfate Saturated S SAmmonium Sulfate Saturated S SAmmonium Sulfide Saturated S SAmmonium Thiocyanate Saturated S SAniline 100% S NA

Antimony Chloride S SBarium Carbonate Saturated S SBarium Chloride Saturated S SBarium Sulfate Saturated S SBarium Sulfide Saturated S S

Benzene Sulfonic Acid S SBismuth Carbonate Saturated S SBlack Liquor S SBorax Cold Saturated S SBoric Acid Dilute S S

Bromic Acid 10% S SBromine Liquid 100% O UButanediol 10% S SButanediol 60% S SButanediol 100% S S

Butyl Acetate 100% O UCalcium Bisulfide S SCalcium Carbonate Saturated S SCalcium Chlorate Saturated S SCalcium Hypochlorite Bleach Solution S S

Calcium Nitrate 50% S SCalcium Sulfate S SCarbon Dioxide 100% Dry S SCarbon Dioxide 100% Wet S SCarbon Dioxide Cold Saturated S S

Carbon Disulphide NA UCarbon Monoxide S SChlorine Liquid O UChlorosulfonic Acid 100% U UChromic Acid 50% S O

Cider S SCoconut Oil Alcohols S SCopper Chloride Saturated S S

Copper Cyanide Saturated S SCopper Fluoride 2% S S

Copper Nitrate Saturated S SCopper Sulfate Dilute S SCopper Sulfate Saturated S SCuprous Chloride Saturated S S

Cyclohexanone U UDextrin Saturated S SDextrose Saturated S SDisodium Phosphate S SDiethylene Glycol S SEmulsions Photographic S S

Ethyl Chloride O UFerric Chloride Saturated S SFerric Nitrate Saturated S SFerrous Chloride Saturated S SFerrous Sulfate S S

Fluoboric Acid S SFluorine S UFluosilicic Acid 32% S SFluosilicic Acid Concentrated S SFormic Acid 20% S S

Formic Acid 50% S SFormic Acid 100% S SFructose Saturated S SFuel Oil S UGlycol S S

Glycolic Acid 30% S SHydrobromic Acid 50% S SHydrocyanic Acid Saturated S SHydrochloric Acid 30% S SHydrofluoric Acid 40% S S

Hydrofluoric Acid 60% S SHydrogen 100% S SHydrogen Bromide 10% S SHydrogen Chloride Gas Dry S SHydroquinone S S

Hydrogen Sulfide S SHypochlorous Acid Concentrated S SLead Acetate Saturated S SMagnesium Carbonate Saturated S SMagnesium Chloride Saturated S S

Magnesium Hydroxide Saturated S SMagnesium Nitrate Saturated S SMagnesium Sulfate Saturated S SMercuric Chloride S SMercuric Cyanide Saturated S S

Mercurous Nitrate Saturated S S

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Methyl Ethyl Ketone 100% U UMethyl Bromide O UMethylsulfuric Acid S SMethylene Chloride 100% U U

Nickel Chloride Saturated S SNickel Nitrate Concentrated S SNickel Sulfate Saturated S SNicotinic Acid S SNitric Acid <50% S O

Nitrobenzene 100% U UOleum Concentrated U UOxalic Acid Dilute S SOxalic Acid Saturated S SPetroleum Ether U U

Phosphoric Acid 0-30% S SPhosphoric Acid 90% S SPhotographic Solutions S SPotassium Bicarbonate Saturated S SPotassium Borate 1 % S S

Potassium Bromate 10% S SPotassium Bromide Saturated S SPotassium Carbonate S SPotassium Chlorate Saturated S SPotassium Chloride Saturated S S

Potassium Chromate 40% S SPotassium Cyanide Saturated S SPotassium Ferri/Ferro Cyanide S SPotassium Fluoride S SPotassium Nitrate Saturated S S

Potassium Perborate Saturated S SPotassium Perchlorate 10% S SPotassium Permanganate 20% S SPotassium Sulfate Concentrated S SPotassium Sulfide Concentrated S S

Potassium Sulfite Concentrated S SPotassium Persulfate Saturated S SPropargyl Alcohol S SPropylene Glycol S SRayon Coagulating Bath S S

Sea Water S SShortening S SSilicic Acid S SSodium Acetate Saturated S SSodium Benzoate 35% S S

Sodium Bisulfate Saturated S SSodium Bisulfite Saturated S SSodium Borate S SSodium Bromide Oil Solution S SSodium Carbonate Concentrated S S

Sodium Carbonate S SSodium Chlorate Saturated S SSodium Chloride Saturated S SSodium Cyanide S SSodium Dichromate Saturated S S

Sodium Ferricyanide Saturated S SSodium Ferrocyanide S SSodium Fluoride Saturated S SSodium Nitrate S SSodium Sulfate S S

Sodium Sulfide 25% to Saturated S SSodium Sulfite Saturated S SStannous Chloride Saturated S SStannic Chloride Saturated S SStarch Solution Saturated S S

Sulfuric Acid <50% S S

Sulfuric Acid 96% O USulfuric Acid 98% Concentrated O USulfurous Acid S STannic Acid 10% S S

Tartaric Acid Saturated NA NATetralin U UTetrahydrofuran O OTransformer Oil S OTrichloroacetic Acid 10% S S

Trisodium Phosphate Saturated S SUrea S SUrine S SWetting Agents S SXylene U U

Zinc Chloride Saturated S SZinc Sulfate Saturated S S

NOTE: Due to the infinite number of potentialcombinations of chemicals and concentrations, it isnot possible to evaluate every situation that may beencountered with Driscopipe HDPE pipe andfittings. Appropriate chemical resistance testingshould be conducted if Driscopipe products are tobe used in a chemical solution that has not beenverified for use with polyethylene.

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FLEXIBILITY The flexibility of polyethylene pipe allows it to be curved over, under, and aroundobstacles as well as make elevation and directional changes. In some instances, the pipe’s flexibilitycan eliminate the need for fittings and reduce installation costs.

Driscopipe HDPE pipe can be bent to a minimum radius between 20 to 40 times the pipe diameter.

TABLE 2: MINIMUM ALLOWABLE BEND RADIUS @ 73.4°F

SDR Minimum Allowable Bend Radius, R a

32.5 > 40 times outside diameter26 > 35 times outside diameter21 > 28 times outside diameter19 > 27 times outside diameter17 > 27 times outside diameter

15.5 > 27 times outside diameter13.5 > 25 times outside diameter11 > 25 times outside diameter9 > 20 times outside diameter7 > 20 times outside diameter

Example: Assume a 24” diameter DR 21 pipe was to be bent. The minimum bend radius can becalculated as follows:

R Da > ×28 Ra > ×28 24" Ra > 672"(56ft)

Where: Ra is the radius of curvature of the bend in the pipe, in.D is the outside diameter of the pipe, in.

The radius of the circular sector (bend) must be greater than 672” (56 ft).

FLOW FACTORS Driscopipe polyethylene pipe has a smooth inside surface. A "C" factor of 150 isrecommended in the Hazen-Williams Formula. Polyethylene pipe has a recommended Manning’s “n”value of 0.009. The smoothness factor, ε, is equal to 7x10-5 ft. Smooth walls and the non-wettingcharacteristic of polyethylene allow higher flow capacity and reduced friction loss with polyethylenepipe.

LIFE EXPECTANCY The hydrostatic design basis for Driscopipe pipe is based on extensivehydrostatic testing data evaluated by standardized industry methods. Based on ASTM D2837,regression curves project a life expectancy of approximately 50 years when transporting water at73.4°F. Internal and external environmental conditions may alter the expected life or change therecommended design basis for a given application.

LIGHTWEIGHT Polyethylene pipe is much lighter than concrete, cast iron, or steel pipe.It is easier to handle and install. Reduced manpower and equipment requirements may result ininstallation savings.

PRESSURE RATINGS Phillips Driscopipe manufactures polyethylene pipe for gravity flow andpressure service through 267 psi at 73.4o F. Some applications or design codes require that the pipebe derated, resulting in lower design pressure ratings. The formulas used to design polyethylenepiping systems include a 2:1 safety factor in hydrostatic stress and a greater than 2:1 safety factor insurge fatigue.

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THERMAL CHARACTERISTICS Polyethylene is a thermoplastic material. Some changes inphysical and chemical properties occur when the system temperature is increased or decreased. Forinstance, the pipe will expand and contract as it is heated or cooled. Temperature must beconsidered when designing a Driscopipe system. The characteristics of polyethylene pipe areestablished at ambient temperature (23°C, 73.4°F). As temperature increases, long-term strengthdecreases, and vice-versa. The maximum recommended operating temperature for Driscopipeproducts is 140°F.

The linear thermal expansion coefficient for Driscopipe pipe is approximately 1.2 x 10-4 in./in./°F.Refer to Driscopipe data sheets for the physical properties of a specific product.

TOUGHNESS Polyethylene has low notch sensitivity, high tear strength, and excellent scratch andabrasion resistance. Its resistance to environmental stress cracking is outstanding.

ULTRAVIOLET PROTECTION Black polyethylene pipe, containing 2 to 2.5% finely divided carbonblack, can be safely stored outside in most climates for many years without damage from ultra-violetexposure. Carbon black is the most effective single additive to enhance the weatheringcharacteristics of plastic materials. Other stabilizers or UV absorbers are not required when carbonblack is used.

In colors other than black, Driscopipe products can be stored outside in sunlight for three to four yearswithout degradation. Colored Driscopipe products use ultra-violet stabilization chemicals to provideprotection during outdoor storage. These products are not recommended for above groundapplications if the pipe will be exposed to sunlight for more than four years.

CAUTIONSDriscopipe products have been used safely in thousands of applications. Still, there areprecautions that should be adhered to when using any product. The following is a listingof some of the cautions that should be considered when using Phillips Driscopipeproducts.

FUSION During the heat fusion process the equipment will reach temperatures of 375o

- 500o F. Caution should be used to prevent burns.

• Review Heat Fusion Cards and Heat Fusion Qualification Guides

WEIGHT Although polyethylene pipe is not as heavy as some alternative pipeproducts, there is significant weight involved. Care should be exercised whenhandling or working around HDPE pipe.

• Know the weight involved! Review Driscopipe size and dimension sheets• Review Phillips Driscopipe’s “Recommendations for Handling and Unloading”

sheet

AIR PRESSURE High pressure air is not recommended for testing Driscopipesystems. Driscopipe products should not be used for process air. Consult yoursupplier for additional precautions.

• • Review the installation procedures in this manual

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STATIC ELECRICITY High static electricity charges can be associated with HDPE pipe products.Improper use of pinch-off equipment and other procedures in the presence of flammable or explosivegases can be extremely dangerous.

• Review the installation guidelines in this manual• Review Driscopipe product brochures

UNLOADING Assure that proper equipment is used when unloading pipe. The equipment should beof a size to handle the loads. The condition of all straps should be checked.

• Review the Driscopipe “Recommendations for Handling and Unloading” Sheet

BURIAL Consult the appropriate authority on trench construction requirements. All safety precautionsshould be taken when working in a trench.

TESTING Water is the recommended test medium. All precautions should be taken for pipemovement and damage during testing.

• Review the installation section of this manual• Review Driscopipe Technical Note #35

IMPACT OR HITTING HDPE pipe is impact resistant. Hitting the pipe with an instrument, such as ahammer, may result in uncontrolled rebound.

• Review product data sheets

PRODUCT CONSIDERATION Some products are not recommended for use in HDPE pipesystems. Consult your supplier for a listing of chemical resistance.

• Review Table 1

COILS Coiled HDPE pipe may contain energy as a spring. Uncontrolled release, i.e. cutting of straps,can result in dangerous, irrepressible forces. Safety precautions and proper equipment are required.

• Review Phillips Driscopipe “Recommendations for Handling and Unloading” Sheet

LOCATING Polyethylene materials are generally not detectable by standard magnetic locatingequipment. There are several methods available to aid in the detection of polyethylene pipelines.These include tracer wires, identification tape, detection tape, line markers, electronic markersystems, acoustic pipe tracing, and “call before you dig” line location. When installing a polyethylenepipe system, consideration should be given to a method or methods that will allow the pipeline to belocated in the future. If posted signs are used to indicate the location of buried pipe, it isrecommended that the signs indicate that the buried line is polyethylene. This alerts the locatingpersonnel that the pipeline may not be identifiable by standard locating equipment. The gas companyshould always be contacted prior to any excavation or trenching.

• Contact utility companies

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DRISCOPIPE® MATERIALS

IDENTIFICATION AND STANDARD DESIGNATION OF PE MATERIALSFor many years, polyethylene piping materials have been identified using codes established in ASTMStandard D 1248, “Standard Specification for Polyethylene Plastics Molding and Extrusion Materials”.This standard classified polyethylene resin according to type, class, and grade. ASTM D 3350,"Polyethylene Plastics Pipe and Fittings Materials", was written in 1974 to allow better identification ofPE pipe materials. Today, ASTM Standard D 1248 is incorporated into D 3350.

ASTM D 3350 uses a cell classification system which allows more specific identification of the PEcompound by using cell classification limits for density, melt index, flexural modulus, tensile strength,environmental stress crack resistance, and hydrostatic design basis. These cells and theircorresponding values are shown in Table3. The color of the pipe and the ultraviolet (UV) stabilizer arealso recognized. For instance, Driscopipe 1000 series pipe is classified as a 345444C according toASTM D 3350. The “3” in the first cell corresponds with a density of 0.941-0.955 g/cm3 when testedaccording to ASTM D 1505. The “4” in the second cell corresponds with a melt index <15 gm/10minwhen tested according to ASTM D 1238. The values for the remaining cells can be determined in asimilar fashion. The new cell classification provides more information about the polyethylenecompound and assures the characteristics of the product are more clearly defined.

ASTM D 3350 also classifies polyethylene resin according to grade. Grade, as defined by ASTM D3350, is a code for polyethylene pipe and fittings materials that consists of two letters that indicate thekind of thermoplastic, followed by two numbers that designate the density and ESCR cell of thethermoplastic. A grade PE34 pipe represents polyethylene (PE) pipe with a density value of “3” andan ESCR value of “4” according to Table 3.

TABLE 3: IDENTIFICATION BY CELL CLASSIFICATION - ASTM D 3350Test Cell Number

Property Method 0 1 2 3 4 5 61. Density,

gm/cm 3D 1505 0.910 -

0.9250.926 -0.940

0.941 - 0.955 > 0.955 N/A N/A

2. Melt Index, Condition E, gm/10 min.

D 1238 > 1.0 1.0 - 0.4 < 0.4 - 0.15 <0.15 N/A N/A

3. Flexural Modulus, MPa (psi)

D 790 <138<(20,000)

138 -<276

(20,000 -<40,000)

276 - <552(40,000 -<80,000)

552 - <758(80,000 -<110,000

758 - <1,103(110,000 -160,000)

>1,103(>160,000)

4. Tensile Strengthat Yield, MPa (psi)

D 638 <15(<2,200)

15 - <18(2,200 -<2,600)

18 -<21(2,600 -<3,000)

21 - <24(3,000 -3,500)

24 - <28(3,500 -<4,000)

>28(>4,000)

5. EnvironmentalStress CrackResistance, a. Test Condition b. Test Duration, hours c. Failure, Max. %

D1693

A4850

B2450

C19220

C60020

6. Hydrostatic DesignBasis, MPa (psi) @ 23 o C.

D 2837 NPRNotPressureRated

5.52(800)

6.89(1,000)

8.62(1,250)

11.03(1,600)

Color and UltravioletStabilizer

ANatural

BColored

CBlack with 2%min. Carbon

Black

DNatural withUV Stabilizer

EColored WithUV Stabilizer

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JOINING POLYETHYLENE PIPE

HEAT FUSION Polyethylene pipe is joined by butt fusion, socket fusion, or electrofusion. Extrusionwelding has been used with some success to fabricate non-pressure, structural components. It is notrecommended for joining pipe to be used in pressurized systems.

MECHANICAL JOINING Driscopipe pipe can be connected mechanically. Flange adapters withsteel or ductile iron back-up rings, mechanical joint adapters, compression couplings, and othermeans are available for joining PE pipe. Each has its own set of advantages and limitations. The usershould be aware of these limitations.

Flange adapters and slip-on back-up rings are available in many sizes. Generally, a PE adapter to aPE adapter does not require a gasket. However, large diameter, high pressure flange adapters mayrequire a gasket. Gaskets are recommended when transitioning polyethylene flange adapters to othermaterials (steel, ductile iron, etc.). Sufficient torque should be applied evenly to the bolts to preventleaks. Re-tightening of the bolts is recommended after the connection has set for a period of time(usually a few hours). Refer to Driscopipe Technical Note #33.

Driscopipe products are joined to bell jointductile iron pipe using a mechanical jointadapter. This adapter uses a gasket seal andis restrained by bolts. Due to the resilience ofthe gasket, retightening of the bolts is notrequired.

Compression type couplings with internal stiffeners are available in some sizes and are generallysatisfactory when temperature changes within the system are small. When using compressioncouplings to join PE pipe, the “pull-out” resistance of the coupling must be considered. The pipeshould be anchored if the expected tensile loading in the pipe exceeds the couplings capability undertensile loading.

Mechanical joining with bolt-on wrap-around clamps is generally not recommended as a permanent,long-term method of joining polyethylene pipe unless the connection is stabilized in some manner.Due to the magnitude of thermal expansion and contraction of polyethylene materials and its creepflow characteristics under load, it can be difficult to maintain a permanent leak-proof seal with certainmechanical wrap-around clamps. They have been used successfully in low pressure or non-pressure,non-critical applications when it is not feasible to flange or fuse the sections together. Heat shrinkable

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polyethylene sleeves have also been used for non-pressure applications to achieve an effective sealbut are also subject to tension pullout with thermal contraction of the pipe.

THREADING & GLUING Threading is not recommended for joining Driscopipe products. Solventcements or adhesives do not bond polyethylene. There is no known cement or glue recommended forjoining Driscopipe products.

DESIGN CONSIDERATIONSThe industries served by Phillips Driscopipe are diverse. The applications within each industry areextensive. Some are clear and straightforward. Others are complex and may require considerationbeyond the scope of this manual.

Proper system design should give consideration to the following design criteria: burial, fluid properties,operating conditions, temperature range, installation, and also the contingencies specific to eachdesign.

BURIAL Tests conducted on Driscopipe pipe at Utah State University by Dr. Reynold K. Watkins showthat it will not buckle under ordinary conditions if the soil envelope is properly compacted and is in fullcontact with the pipe. Compaction to 85% Standard Proctor Density (AASHTO T-99) should beconsidered a conservative minimum. ASTM D 2321, “Standard Recommended Practice forUnderground Installation of Flexible Thermoplastic Sewer Pipe”, should be used as a guide fordetermining the method of placing and compacting the backfill.

FLUID PROPERTIESCHEMICAL COMPATIBILITY Driscopipe high density polyethylene pipe does not react withmost products being piped. There are some strong chemicals which affect it. Whenreviewing Table 1, it is helpful to keep the following three factors in mind.

1. The chemical resistance of Driscopipe products is related to the chemicalitself, the operating temperature and the concentration of the chemical.

2. Strong oxidizing agents such as nitric acid, sulfuric acid, chlorine gas, andliquid bromine are most aggressive and deserve special consideration.

3. Permeation of the pipe wall is negligible for most products. However,aromatic hydrocarbon permeation rates should be reviewed.

DENSITY A close approximation should be made of the fluid’s density or specific gravity forlater use in flow calculations and/or installation calculations.

SOLIDS CONTENT HDPE pipe and fittings are used to convey many slurry mixtures. Someare primary processing pipelines. Some are secondary waste conveying pipelines. Thesystem designer should consider the slurry solids content, its particle structure, abrasivenature, size distribution, and net specific gravity.

OPERATING CONDITIONS

SYSTEM PRESSURES Since few pipelines operate at a stable pressure, the engineershould accurately determine the system’s design operating pressure. Typically, this is thehighest pressure at which the system is expected to operate. An additional safety factor is

11

gained when the system is operating at lower pressures. In addition, the engineer mustrecognize the interdependence of the operating pressure and the operating temperature.

FLOW REQUIREMENTS Polyethylene pipe has a smooth wall. Compared to steel orconcrete, smaller diameter polyethylene pipe can often carry the same fluid flow at the samepressure as the concrete or steel pipe. This makes polyethylene an ideal choice for reliningpipes while maintaining flow capabilities.

SURGE PRESSURES (Water Hammer) When flow in a fluid system is stopped quickly,surge pressure can occur. Driscopipe HDPE pipe can absorb significant surge pressures. Inaddition, surge pressures in Driscopipe systems are typically lower than other pipingmaterials. As with all systems, limitations in this area should be examined.

VACUUM Vacuum systems using HDPE pipe have operated successfully for many years.Due to the long term “creep” properties of polyethylene, the appropriate DR should be used.

In full flow gravity lines, a siphon or vacuum condition can develop when sudden changes inelevation are encountered. When vacuum is expected, Driscopipe systems must beengineered to prevent pipe collapse. In gravity flow situations, the vacuum can be “broken” byan air intake valve. Refer to Table 9 in the design section of this manual to review vacuumcapabilities.

TEMPERATURE RANGEThe temperature of the fluid being conveyed will have an effect on the service capability ofDriscopipe HDPE pipe. As with all thermoplastic piping, polyethylene pipe loses stiffness andtensile strength as temperature increases. As temperature rises, the normal operatingpressure of the pipe must be derated. A heavier wall pipe can be specified to hold the samepressure at higher temperatures.

As the temperature decreases, Driscopipe products gain strength. The pipe may be designedto hold rated pressure at 73.4oF with recognition of a greater safety factor at lowertemperatures.

Allowances for thermal expansion and contraction should be engineered into any installationbased upon the fluid or environmental temperature.

INSTALLATION CONSIDERATIONS

LOADS ON SUPPORTED OR SUSPENDED PIPELINES Support must befrequent enough to minimize deflection from the weight of the pipe and contents. Supportscan also be used to control or restrain movements due to thermal expansion and contraction.

LOADS ON EXPOSED, ABOVE GROUND PIPELINES Pipelines laid overland areexposed to numerous hazards. From day to night and season to season, the pipe willnaturally expand and contract. Movement should be controlled by such means as snaking,anchoring, or shallow trenching.

In summer temperatures, the pipe will typically become heated. This will decrease thepressure rating of the pipe. As the winter temperature decreases, the safety factor on pipepressure is increased.

LOADS ON BURIED, UNDERGROUND PIPELINES Buried installations mustconsider earth loading and loads from external sources such as traffic, nearby structures, andpotential hydrostatic heads. If changes in system temperature are expected, control ofthermal expansion should be considered.

12

LOADS ON BURIED, MARINE PIPELINES Driscopipe HDPE pipe is an excellentchoice when installing marine pipelines. It is lighter than water and will float. Design of buriedmarine pipelines should include methods to anchor or secure the pipeline in place. If thepipeline is not entirely filled with water at all times, the anchor weights should be increased tomaintain the appropriate amount of buoyancy under all operating conditions. The designershould also consider anchoring the pipe as it enters or leaves the water.

Polyethylene pipe may be buried in marine installations, but it is not required. Considerationshould be given to possible damage from boat anchors, debris, and current action as well asthe potentially weak support capacity of the bottom material.

Driscopipe HDPE pipe is typically floated into position with the anchor weights attached.Then it is filled with water and allowed to sink into place. This process must be controlled toaccurately place the pipeline and to minimize excessive strain on the pipe during the sinkingprocess.

LOADS ON BURIED, MARSHLAND PIPELINES Marshy installations do notsimply imply those areas filled with peat moss and weeds. It also includes areas where thesoil may become liquefied or fluidized. Under such conditions, the pipe may be easilydisplaced in the soil. Driscopipe HDPE pipe can be weighted to provide “neutral” buoyancy inmost conditions. The combination of soil loads, water loads, buoyancy, and soil support mustbe considered.

LOADS ON EXPOSED, WATER SURFACE PIPELINES Even when filled withwater, Driscopipe HDPE pipe will float on the water surface. As a float or a floating pipeline,consideration should be given to wind forces and wave action. Possible damage by boats orfloating debris is also a concern. When the pipe is used for process fluids that may vary indensity (e.g. dredge lines), additional flotation should be considered.

LIVE TRAFFIC LOADS Traffic operating over or near a buried pipeline causes the earthto move slightly under its weight. This causes a dynamic load transfer from the vehicle to theground. The heavier the vehicle, the greater the load transfer. To distribute and reduce theload on the pipe, it can be buried deeper and/or located farther from traffic. The stress on thepipe may also be reduced by increasing the soil compaction (density). The system designershould review the various traffic weight classes, soil compaction factors, and the associatedstress.

OTHER CONSIDERATIONS

STATIC ELECTRICITY Electrical charges are generated on polyethylene pipe by friction. Theflow of air or gas containing particulate matter can build up significant static charges. Polyethylenepipe should not be used to convey dry materials. Examples include grain chutes and pneumatictransfer systems. Static charges can also occur when particles strike the exterior of the pipe. Thismay occur in areas where polyethylene transporting a gas is damaged and leaking. Static chargesare a safety hazard, particularly in areas where there is leaking gas or an explosiveatmosphere.

Plastic pipe does not conduct electricity and static charges will remain in place until some groundingdevice comes close enough to allow it to discharge. The result will vary from an slight physical shockto a possible fire if a flammable gas-air mixture is present. The potential for a static discharge can beminimized by applying a film of water with a 5% soap solution to the pipe’s surface to drain away thestatic electricity. Since the plastic pipe is a non-conductor, a ground wire installed on the plastic pipewill only discharge static electricity in a small, localized area.

When workers must enter a bellhole to hot tap a line or make emergency repairs to a damaged orleaking line, it is important that all safety precautions be observed. If the potential for static charges

13

exists, the surface of the polyethylene pipe should be doused with soapy water before entering thearea. A 5% soap solution enables the water to form a continuous film on the pipe rather than formingunconnected droplets. A wet cloth dipped in the soap solution should be kept on the pipe to drain offstatic charge that may build up while working on the line.

ANIMAL AND INSECT ATTAC K Polyethylene pipe will not support bacterial growth. It is notdigestible. Therefore, it holds no food value for insects, earthworms, marine worms, or smallmammals. Because Driscopipe is smooth and inert, it is difficult for marine growths and algae toadhere.

MISCELLANEOU S The engineer should be aware of the total environment in which the Driscopipesystem is to be used. As with any other pipeline, pump cavitation and vibration should be eliminatedor minimized.

Driscopipe products cannot be located by metal detectors. If a buried pipeline needs to be traced, atracer wire should be buried above the pipe.

When polyethylene pipe is being used near a heat source, the pipe should be insulated from the heator appropriate design temperature service factors should be applied when calculating systempressure ratings.

Hydrocarbons do not attack the pipe but will permeate the pipe wall causing swelling and loss ofstrength. These effects are reversible. Heavier wall pipe should be selected to provide adequatestrength for the pipeline pressure.

NOTE: When Driscopipe HDPE pipe is used to transport potable water, it should not be direct buriedin soils contaminated by hydrocarbon fuels or other chemicals known to affect polyethylene. Dualcontainment of the HDPE pipeline should be considered. Furthermore, polyethylene should not beinstalled where there is a high risk of petroleum or chemical spills. In these applications, no pipingsystem, whether it is plastic or metal, can be considered immune to contamination by permeationthrough the walls or joints. If the contaminating source cannot be safely controlled, it is best to changethe piping route altogether.

DISINFECTING For potable water systems using chlorine as a disinfectant, it is recommended tolimit the chlorine dosage to 25 mg/L free chlorine with a residual of 10 mg/L at the end of the 24 hourstand period. The disinfectant is flushed per the requirements of AWWA C651, Standard forDisinfecting Water Mains. The daily amounts of chlorine should not exceed 3 ppm.

CONTINGENCY AND RISK

In some cases, there is justification for the selection of a pipe size or wall thickness other than thatdetermined through an engineering analysis. For example, a thicker pipe is often specified for a slurryapplication to maintain the desired pipe pressure rating as the wall wears over time.

Upgrading may also be a contingency against unknowns such as variable operating conditions,system abuse, suspicious soil conditions, etc. Use of a thicker wall will reduce hoop stress andincrease the factor of safety. In situations where the risk of damage is high or when serious economicconsequences may result from a failure, the engineer may wish to provide an additional safety factorin the design of the pipeline.

14

DRISCOPIPE®

SYSTEMS DESIGNDesign of a Driscopipe system is straightforward, but operating conditions can be extremely diverse.Based on the project’s operating requirements, a pipe with the correct pressure capability is selected.Then, a size designed to transport the required flow is chosen. The design is completed by evaluatingthe pipe’s ability to function when properly installed.

The following guidelines are typical considerations when designing a Driscopipe system. Due toproject requirements, it may be necessary to approach the design procedure in a different order.

GUIDELINES:• Determine pipe wall thickness (DR) to meet the project’s pressure requirements.• If required, derate the pipe (DR) based on system operating conditions.• Evaluate the system’s flow requirements to determine the pipe size.• Verify the pipe’s ability to function under planned installation conditions. Examples

include burial calculations, thermal effects, etc.• Adjust the pipe wall thickness as required for external loads.• Review the final pipe size and wall thickness to meet flow, pressure, and external load

requirements when the system is installed and operated as designed.

SYSTEM PRESSURE REQUIREMENTSMost pipeline systems are designed for one of three types of service: a) pressurized flow, b) gravityflow, or c) vacuum flow. When designing a pressurized pipe system, the pipe selected must hold theinternal pressure safely. In a non-pressurized system such as a gravity flow sewer, pipe selectiondepends on structural and flow factors. Vacuum piping systems must resist collapse. For eachinstallation, the design engineer will use different design criteria and calculations

DIMENSION RATIO Polyethylene pipe design is based on the “Dimension Ratio” of the pipe,typically abbreviated as “DR”. By definition, dimension ratio is the ratio of the pipe’s outside diameterto its minimum wall thickness. This ratio may also be referenced as the “SDR” or “StandardDimension Ratio” of the pipe.

DROD

t=

Where: DR = Dimension Ratio (also called Standard Dimension Ratio)OD = Pipe outside diameter, inchest = Pipe minimum wall thickness, inches

For a given DR, the ratio of the outside diameter to the minimum wall thickness remains constant.The outside diameter of DR 11 pipe is eleven times the wall thickness. This is true for all diameters.For high DR ratios, the pipe wall is thin in comparison to the pipe outside diameter. For low DR ratios,the wall is thick in comparison to the pipe outside diameter.

DESIGN PRESSURE RATINGS The hydrostatic design basis of Driscopipe products isestablished using the procedures defined in ASTM D 2837. The hydrostatic design stress (S) iscalculated by dividing the hydrostatic design basis (HDB) by a typical safety factor of 2.0. This factorof safety is an industry accepted standard designed to preserve the integrity of the pipeline as well asto protect the public. Safety factors used to calculate the hydrostatic design stress vary by industryand regulatory agencies.

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TABLE 4: HDB VALUES FOR MEDIUM AND HIGH DENSITY POLYETHYLENE

PE 2406 PE 3408

Hydrostatic Design Basis(73.4°F @ 100,000 hours) 1250 psi 1600 psi

Hydrostatic Design Stress 630 psi 800 psiSafety Factor 2.0 2.0

Use of a higher design stress may reduce the factor of safety and shorten the service life of the pipingsystem. The prudent engineer will double-check the hydrostatic design stress according to theindustry accepted formula as defined in ASTM D 2837.

( )P2St

t=

−D

Where: P = Working Pressure Rating (WPR) S = Hydrostatic Design StressD = Average Outside Diameter t = Minimum Wall Thickness

POSITIVE PRESSURE PIPELINES The pressure rating of thermoplastic pipe is calculated fromDR and hydrostatic design stress. Polyethylene pipe with a numerically high DR has a lower pressurerating than pipe with a low DR. In other words, as DR decreases, pressure rating increases, and viceversa.

The formula relating DR and hydrostatic design stress has been adopted by ISO (InternationalStandards Organization), ASTM (American Society For Testing and Materials), and PPI (Plastics PipeInstitute) as the standard for the industry.

The formula is:

P2St

OD t=

− or P

2SDR 1

=−

Where: P = Working Pressure Rating, psiOD = Pipe Outside Diameter, in.S = Hydrostatic Design Stress, psit = Minimum Wall Thickness, in.DR = OD/t

All pipe of the same DR (regardless of diameter) has the same pressure rating for a givendesign stress . Pressure ratings for PE 3408 materials are shown in Table 5. These values arebased on industry standard design conditions using water at 73.4oF and a hydrostatic design stress of800 psi.

16

TABLE 5: WORKING PRESSURE RATINGS (WPR) FOR DRISCOPIPE

PE3408 PIPE AT 23°C (73.4°F)

Dimension Ratio 32.5 26 21 19 17 15.5 13.5 11 9 7Pressure Rating, psig 51 64 80 89 100 110 128 160 200 267

Note: This chart is only valid at temperatures at or below 73.4°F; Please refer to Table11 for higher temperature ratings.

WATER HAMMER/ PRESSURE SURGE Flowing liquid has momentum and inertia. When flowis suddenly stopped, the mass inertia of the flowing stream is converted into a shock wave. Highstatic head exists on the pressure side of the pipeline. Some of the more common causes ofhydraulic transients are opening and closing (full or partial) valves, starting and stopping pumps,changing turbine speed, reservoir wave action, liquid column separation, and entrapped air.

Quick surge pressures are shock waves known as “water hammer”. The pressure wave due to water hammerraces back and forth in the pipe getting progressively weaker with each “hammer”. Maximum surge pressureresults when the time required to change a flow velocity a given amount is equal to or less than 2 L/S suchthat:

t2LS

≤

Where: L = Length of the pipeline, ftS = Speed of the pressure wave, ft/st = Time, s

S is determined from: ( ) ( )( )S 12K E

= ××

× + ×w g E K DR/

Where: S = Speed of the pressure wave, ft/sK = Bulk modulus of the liquid, psi = 300,000 psi for waterE = Modulus of elasticity of pipe material, psi = 100,000 (short term)DR = Dimension Ratio of pipe w = Unit weight of fluid, lbs/ft3

g = Acceleration due to gravity = 32.2 ft/s2

The excess pressure due to water hammer is: PwSV144gs

c=

Where: Ps = change in pressure, psiVc = change in velocity, ft/s occurring within critical time 2L/S

w, g and S are as above.

EXAMPLE: Water is flowing in a Driscopipe pipeline with a DR of 32.5 at a velocity of 10 ft/sec.Determine the maximum pressure increase when a valve is closed in a time equal to or less than 2L/S.

Where: DR = 32.5 K = 300,000 psi E = 100,000 psi

17

S ft s= ××

× +=12

300 000 100 000

62 4 32 2 100 000 300 000 32 5476

( , , )

( . / . ) ( , ( , )( . )/

P psiS =× ×

×=

62 4 476 10

144 32 264 1

.

..

When the time to stop flow is greater than 2L/S, the change in pressure can be minimized. Particularattention should be given to the final portion of valve closure. This is the time of maximum effect onthe velocity of the flowing liquid. The actual increase in pressure caused by valve closure is difficult todetermine but a closure time of 10 times 2L/S for a gate valve with linear closure characteristicsshould reduce the pressure surge to the range of 10% to 20% of the surge caused by closure in atime equal to or less than 2L/S.

In general, good system design will eliminate quick opening/closing valves. The design engineershould use judgment with regard to surge pressures when selecting the thickness of the pipe. Thefollowing rules of thumb may be of help:

• Surge pressures in polyethylene pipe are significantly less than those encountered in rigid pipe under the same conditions.

• Occasional shock pressures can be accommodated within the design safety factor. Due tothe short time duration of the surge pressure, occasional shock wave surge pressures to 2.0times the DR pressure rating at 73.4°F are usually allowable.

• If surge pressure or water hammer is expected in a system, maintain the flow velocity of thesystem at a conservative level.

• If surge pressure or water hammer is expected, maximize the time required to shut off a valveor reduce flow. A shutoff cycle 6-10 times the time period 2L/S is suggested to minimizesurge pressures by gradually slowing the fluid flowstream. If constant and repetitive surgepressures are present, the excess pressure should be added to the nominal operatingpressure when selecting the pipe DR.

LONGITUDINAL STRESS FROM INTERNAL PRESSURE When a fully restrained pipelineis pressurized, longitudinal stresses develop in the pipe wall. The longitudinal stress is calculated asfollows:

SP OD t

tL =−µ ( )

2Where: SL = Longitudinal tensile stress, psi µ = Poisson’s ratio ( = 0.45 for HDPE)

P = Internal operating pressure, psi OD = Pipe outside diameter, in.t = Pipe wall thickness, in.

Most pressurized pipe systems operate under a dual state of hoop stress and longitudinal stress. Thelongitudinal stress factor is already included in the pipe’s pressure rating.

FLUID FLOW Polyethylene pipe has excellent flow properties. Because polyethylene pipe has lessdrag and less turbulence at higher flows, it may carry a greater volume of fluid than steel, cast iron, orconcrete pipe of the same size. Driscopipe HDPE pipe is corrosion resistant and less susceptible todeposits and bacterial growth. Unlike other piping materials, polyethylene will retain these flowcharacteristics over its service life.

INITIAL FLOW ESTIMATES When the inside diameter of a particular pipe size is known and anominal velocity is chosen, the flow rate (gpm) can be calculated using:

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1.) Q = 2.449 V(ID)2 2.) ID 0.639QV

= 3.) VQ

ID2=

× 0 408.

Where: Q = Gallons per minute, gpmV = Velocity, ft/sID = Inside Diameter, in.

Using these formulas, the engineer can calculate an approximate inside diameter, flow rate, or flowvelocity when the other two variables are known or estimated.

PRESSURIZED FLOW Many equations are available to show the relationship between fluid flowand pressure drop in a given pipeline. The equations typically involve a friction factor based on thepipe material.

Darcy-Weisbach is one commonly used equation. The Darcy-Weisbach equation requires the Moodyfriction factor diagram or an equation to calculate the friction factor of the pipe based on its relativeroughness. The smoothness factor for Driscopipe is ε = 7x10-5 ft or ε = 8.4 x 10-4 in.

The Darcy-Weisbach equation and the Colebrook-White expression for the friction factor are shownbelow. The Moody diagram has not been reprinted but is available in a number of reference books.

Darcy-Weisbach: h ff =Ld

V2g

2

Colebrook-White: 1

f2 log

2.51

Re f

/ d3.7

= − +

ε

Where:hf = Friction head lossd = Inside diameterV = Velocityg = Gravitational accelerationf = Friction factorε = Smoothness factorRe = Reynolds numberL = Length

For a simpler solution to fluid flow in Driscopipe HDPE pipe, consider the Hazen-Williams formula.

THE HAZEN AND WILLIAMS FORMULA:

∆P452QC D100

1.85

1.85 4.86=

19

Where:

∆P100 = Friction pressure loss, psi per 100 feet of pipeQ = Rate of flow, U.S. gpmC = Pipe coefficient (see Table 6)D = Inside diameter, in.

The coefficient C is essentially a friction factor. Table 6 outlines “C” values for various types and agesof pipe. The designer must use proper judgment to select pipe sizes that best meet the projectconditions.

The following may be helpful:

• At a given flow rate, a larger diameter pipe will have a lower velocity andless pressure drop.

• At a given flow rate, a smaller diameter pipe will have higher velocity andincreased pressure drop.

• The frictional head loss is less in larger diameter pipes than smaller pipeflowing at same velocity.

TABLE 6: “C” VALUES FOR HAZEN AND WILLIAMS FORMULA *

Constant Type of Pipe150 Driscopipe HDPE pipe

140 New steel pipe or tubingGlass tubingAsbestos cement

130 Copper tubingCast iron- new

125 Steel pipe- old

120 Wood stave pipeConcrete pipeCast iron pipe- 4-6 years old

110 Cast iron pipe- 10-12 years oldGalvanized steel

100 Cast iron pipe- 13-20 years oldGalvanized steel- More than 5 years old

90 Cast iron pipe- 26-30 years old

60 Corrugated steel pipe

*Historically, Driscopipe has published a C Factor of 155. This was based on testing conducted in the 1970’s. Similartesting was repeated in 1995. Using state of the art measurement technology, the same laboratory established a CFactor near 153. As a conservative design parameter, Phillips Driscopipe now states a C Factor of 150. For many years,Driscopipe systems have been designed and have proven their performance with a C factor of 155.

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FITTING PRESSURE DROP Fittings increase head loss in a system. To calculate the effect offittings on a system’s flow, the fittings are converted to “equivalent” feet of pipe. The inside diameterof the fitting (ft) is multiplied by the appropriate ratio to calculate an “equivalent” length (in feet) of pipe.This value is added to the total footage of the piping system when calculating the total systempressure drop.

These equivalent lengths should be considered an approximation suitable for most installations.

TABLE 7: EQUIVALENT LENGTHS FOR ESTIMATING PRESSURE DROP THROUGHFITTINGS

Fabricated Fitting Equivalent LengthRunning Tee 20 DBranch Tee 50 D90o Fab., Ell 30 D60o Fab., Ell 25 D45o Fab., Ell 18 D45o Fab., Wye 60 DConventional Globe Valve (Full Open) 350 DConventional Angle Valve (Full Open) 180 DConventional Wedge Gate Valve (Full Open) 15 DButterfly Valve (Full Open) 40 DConventional Swing Check Valve 100 D

Fabricated fittings are manufactured from segments of pipe using butt fusion. Due to geometricconsiderations, the pressure rating of fabricated tees, wyes, and elbows is approximately 75% of thepressure rating of the pipe used to make the fitting. To obtain a completely pressure rated system,fabricated tees, wyes, and elbows should be chosen from a heavier wall pipe (lower DR). Alternately,the fitting may be externally reinforced to bring it to the full pressure rating.

The need for reinforcement, encasement, or other support should be evaluated for each installation.

PRESSURE LOSS FOR VISCOUS FLUIDSWATER BASE FLUIDS For water base fluids with viscosities different from pure water, an estimateof the pressure loss can be calculated by multiplying the Hazen-Williams frictional pressure loss bythe specific gravity of the fluid.

NON-WATER BASE FLUIDS When the Reynolds number of flow in pipes is less than 1200, viscousflow exists. The Reynolds number can be calculated from:

Re.

=50 7Q

d

ρµ

Where: Q = flow rate, gpm ρ = density of fluid, lbs/ft3

d = inside diameter, in. µ = absolute (dynamic) viscosity, centipoise

The pressure drop for viscous flow typical of some oils and liquids other than water can be calculatedfrom:

∆PQ

d100

0 0237=

×. µ4

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GRAVITY FLOWGravity flow systems transport fluids without pumping. They are typically non-pressure systems. Insome installations, water head may cause pressure in a gravity flow system. Some may operate withfull flow and some may operate partially full.

FULL FLOW Selection of Driscopipe HDPE for a full flow gravity system requires: (1) the flow raterequirement in gallons per minute, (2) the slope of the pipeline, and (3) identification of an appropriatepipe inside diameter. Based upon a full flow situation, the flow rate in gallons per minute can becalculated from the Manning equation:

THE MANNING FORMULA:

The volumetric flow rate in a gravity system can be determined from the Manning formula:

Q AR Sh= 98 32

312.

Where: Q = Flow rate, gpmRh = Hydraulic radius, in., cross-sectional flow area divided by wetted perimeterRh = ID/4 for full flow

S = Slope, ft/ftV = Velocity, ft/sA = Cross-sectional flow area of the pipe, in2

Note: The above formula is a derivation of the Manning formula and includes a “n” value of 0.009

The velocity, inside diameter, and slope can be calculated by the following equations:

VQ

A=

0 320.

IDQ

S=

0 0327912

2 67.

.

SQ

ID=

0 001075 2

5 34

..

PARTIAL FLOW A gravity pipeline will carry more liquid when running 85%-95% full than when100% full.

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TABLE 8: CHANGES IN VELOCITY AND FLOW CAPACITY AS A FUNCTION OF FULL FLOW

% Full

Velocity

(As a % of Full Flow)

Flow Capacity

(As a % of Full Flow)

100 100 10095 111 106.390 115 107.380 116 9870 114 8460 108 6750 100 5040 88 3330 72 1920 56 910 36 3

Usually, a partially full gravity flow pipeline is evaluated as a full flow pipeline of a different, but smaller,“equivalent” diameter. The equivalent diameter matches all the hydraulic characteristics of the larger,partial flow gravity pipeline. The velocity, GPM flow rate, and slope are identical in each case. Theequivalent diameter is four times the hydraulic radius (DE = 4 x Rh). The hydraulic radius for partial flowgravity pipelines is defined as the ratio of the cross-section flow area divided by the wetted perimeter.

EXAMPLE: At a slope of 0.01 ft/ft, 20” I.D. Driscopipe HDPE pipe will carry approximately 9000 gpmat a velocity of 9.0 ft/s at full flow. From Gravity Full Flow chart, What will it carry if flow is 15” deep?

D

DP

F

= =15

200 75

"

".

Q QP F= × = × =0 91 9000 0 91 8190. . gpm

V VP F= × = × =115 9 0 115 10 35. . . . ft/s

In gravity flow systems, there is no supporting internal pressure. The pipeline must be able to supportany external water table over the long-term per Table 10. If there are areas where siphon (vacuum)effects are anticipated, the internal vacuum (in feet of water) must be added to the external hydrostatichead as an apparent external pressure. When a pressurized forced main is in operation, the internalpressure often exceeds any external hydrostatic head.

SLURRIES A slurry is a two-phase mixture of solid particles in an aqueous phase where the twophases do not chemically react and can be separated by mechanical means. Slurry systems aredivided into two types:

1. Non-settling slurries 2. Settling slurries

Non-settling slurries take on the flow characteristics of a viscous fluid. Such slurries are designedaccording to standard procedures with allowances for the higher viscosity. Most slurry applicationsare of the “settling” type. The solids tend to settle out of the carrier fluid. As the flow velocity is

23

reduced, the fluid flow goes through settling phases. Settling tendencies are often countered byincreases in flow velocity.

FLOW PHASES Changes in the flow velocity of a slurry affect the mode of flow. If the flow velocity isinitially high and then is gradually slowed, the slurry will pass through four flow modes:

• Homogeneous Flow: This term describes a system in which the solids are uniformlydistributed throughout the liquid. This is the most desirable of all flow modes becausethe particles do not contact the wall as frequently, thus reducing abrasion.

• Heterogeneous Flow: The solids tend to flow nearer the bottom of the pipe but donot actually slide on the pipe bottom. This is the most economical flow mode and istypically used for sand sized solids.

• Saltation Flow: In this mode, solid particles tend to bounce along the bottom of thepipe. This flow is particularly aggressive in its abrasion of pipe. Due to the resilienceof Driscopipe polyethylene pipe, the particles tend to bounce and rebound. In steelpipe, the particles work-harden the wall surface and chisel away at the steel.

• Sliding Bed Flow: This mode of flow is generally unsatisfactory. Solids slide and rollon the pipe bottom. Excessive erosion along the pipe bottom occurs rapidly.Blockages can occur frequently.

The sliding bed and saltation modes can often be upgraded into homogeneous and heterogeneousmodes by increasing flow velocity. However, the operational cost (i.e., power requirements) couldincrease significantly.

CRITICAL VELOCITY When the flow velocity of a slurry is below the critical velocity, the solidparticles tend to drop out of suspension and settle to the bottom of the pipe. The critical velocity isdetermined by the particle size and shape, size distribution, concentration, particle density, and carrierfluid density.

CRITICAL “TRANSITION” VELOCITY Some solids (e.g. fine fly ash) form a viscous fluid with theliquid carrier. When the flow velocity of such fluids makes a “transition” from the turbulent flow regionto the laminar flow region, the viscous, homogeneous fluid changes from a smooth mixture to aseparated mixture. When turbulence stops and laminar flow develops, the homogeneous mode offlow ends and the saltation or sliding bed mode begins. Turbulent flow is necessary to keep the solidsin suspension. The following rules of thumb should be helpful in designing a pipe system for this typeof slurry:

• As the slurry viscosity increases, the flow velocity must be increased to prevent settling.• As the solids concentration increases, the flow velocity must be increased to prevent settling.• As the particle size increases, the flow velocity must be increased to prevent settling.• Slurries with high concentrations of fine size particles can be more abrasive than slurries with

larger size particles. The basic reason is that the particle/wall contact is greater and morefrequent with a “fine” slurry.

CRITICAL “DEPOSITION” VELOCITY Some particle solids will form a heterogeneous suspensionrather than a viscous, homogeneous fluid. In horizontal flow, the inertia and weight of the particle arepredominant. Even at full flow, the concentrations of solids along the bottom of the pipe are greaterthan at the top. At the critical velocity, the weight of the particle exceeds the carrier fluid’s suspensioncapability, and the solid begins to form deposits on the bottom of the pipe. The critical velocity,therefore, is a deposition velocity. The deposition velocity, usually turbulent, is a function of particlesize, particle density, and solids concentration. For example, high concentrations of large, heavygravel in flowing water must be maintained at a fairly high velocity to prevent settling. The following“rules of thumb” should be helpful in designing a pipe system for such a slurry:

24

• As the particle “fall” velocity increases, the deposition velocity must be increased to maintain aheterogeneous flow.

• Generally speaking, as particle size increases, the deposition velocity must increase.• As the density of the solids increases, the deposition velocity must increase.• As the concentration of the solids in the fluid increases, the velocity must increase.• As the pipe diameter is increased, the deposition velocity must be increased to maintain

turbulence and prevent settling.• The deposition critical velocity represents the lower limit of safe operations due to increased

abrasion, solids, bed buildup, and plugging.

DUAL CHARACTER SLURRY Many commercial slurries are of a mixed character exhibitingbehavior of both “deposition” and “transition” settling. The size distribution of the solids may permitthe “fines” to join the fluid to form a homogeneous, viscous flow pattern, while the coarse solids areheterogeneously suspended. A coal slurry is a good example of this dual behavior. For theseapplications as well as for long-distance slurry pipelines, the design engineer should considerturbulent flow for the full length of the pipeline. These additional rules of thumb and design hints maybe helpful in a specific application:

• Generally, the smaller the particle, the easier it is to transport in a slurry.• The particle shape affects the settling rate (fall velocity) of the particle in the fluid.• The more spherical the particle, the faster it settles.• Heavier particles require higher transport velocities.• Heavier transport fluids such as saltwater reduce the weight of the particle through

buoyancy and will reduce settling velocities and transport velocities.• The use of viscous fluids such as fine slurries or oils reduces settling velocity. Thus,

slower transport velocities can be used for large, heavy solids.• Generally, slurries are pumped at a concentration of less than 25% by volume.• Slurries are usually specified in terms of concentrations by weight. Such

specifications should normally follow the previous criterion, taking into account thebulk density of the solids.

FIGURE 1: EXAMPLES OF CRITICAL FLOW FOR VISCOUS SLURRIES

AND SLURRY TAILINGS

SLURRY APPLICATIONS Driscopipe HDPE pipe is excellent for transporting many different kindsof slurries. Typical slurry applications include dredging lines, coal or limestone slurry, wood chips,sand, mine tailings, and many others. Slurry pipelines are usually installed above ground. Thisprovides easy access to lines if plugging should occur. Furthermore, the pipe can be rotated todistribute wear more evenly around the inside diameter of the pipe.

Slurry Critical FlowTotal Suspension Sub-Critical Velocity

Viscous Slurry “Transition Settlin g”

Slurry Critical FlowTotal Suspension Sub-Critical Velocity

Slurr y Tailings “Deposition Settling”

Full Turbulence Transition to Laminar FlowResulting in Separation

Full Movement Slow Velocity Resultingin Bed Buildup

25

Grade changes in slurry pipelines should be gradual. Exercise caution when slopes becomeexcessive. Turbulence often increases abrasion. Drop boxes are often used to reduce turbulence.They are also used to relieve pressure buildup caused by surface gradients. Drop boxes aregenerally used on gravity lines. However, pressure lines can also empty into drop boxes. Design ofthe drop box should allow the slurry to fall freely into the fluid in the bottom of the box or utilize arubber liner on the wall opposite the inlet pipe.

It is difficult to predict actual wear characteristics when using polyethylene pipe to transport slurries.Every application has different parameters. When transporting slurries with Driscopipe products,minimum wear will occur when velocity is minimized and solids are kept in suspension. A maximumvelocity of 12-15 feet per second is preferred. It is generally recommended that very sharp abrasivessuch as bottom ash should not exceed 10 feet per second. A solid concentration below 25% byvolume with particle size of ¼” or less is generally recommended. System temperatures at or nearambient are preferred. Maximum wear and flow properties will be obtained if long radius elbows,sweep elbows, and molded flange adapters are used in the installation.Driscopipe products will withstand some abrasive particles along the inside of the pipe.However, turbulent solids can be harmful to polyethylene pipe when the solids impinge directlyon the inner wall or at very sharp angles. For instance, in a dredging operation, the section ofpipe directly off the pump may experience excessive wear due to increased turbulence andvibration.

VACUUM OR SUCTION PIPELINES

Driscopipe HDPE pipe may be subjected to internal pressure or internal vacuum. Vacuum systemsusually can be categorized into one of three general situations applicable to most installations. Thoseare vacuum pipelines above ground, vacuum pipelines underwater (submerged), and underground(buried) pipelines.

Typical applications for above ground vacuum pipelines could be:

• Moisture removal (dryer) suction lines in a paper mill.• Suction lines for a dredge barge.• The down-hill run of a large-diameter gravity-flow siphon line.

When a vacuum condition exists in a pipeline, the pipe wall must be selected to resist the collapsingforces. The dimension ratio of the pipe governs the amount of vacuum a pipeline can support on ashort-term or long-term basis. Selection of a thicker wall pipe will allow the system to operate underhigher vacuum conditions.

Phillips Driscopipe conducted extensive testing to develop data for practical, industrial installationswhich would provide for long term vacuum service with a high degree of confidence and reliability.The tests examined sections of various DR pipes in a controlled and monitored environment. Thedata derived incorporates the pipe DR, ovality, acceptable tolerances in wall thickness, and timeduration of various stress levels. The aboveground vacuum capabilities given in Table 9 are thepractical, maximum levels of vacuum that Driscopipe HDPE pipe of a given DR can support.

26

TABLE 9: DIFFERENTIAL PRESSURE (VACUUM OR EXTERNAL FLUID) CAPABILITYFOR UNSUPPORTED PIPE @ 73.4°F

Service Life Units 7 9.3 11 17 19 21 26 32.5psi 189 146 87 28 21 16 8 4

1 Day Feet of Water 437 337 202 65 48 36 18 10Inches of Mercury 386 298 178 57 42 32 16 9

psi 108 83 64 15 12 11 4 2

1 Month Feet of Water 249 192 147 34 28 25 10 6Inches of Mercury 220 170 130 30 25 22 9 5

psi 100 78 48 14 9 8 4 2

1 Year Feet of Water 232 182 111 32 23 19 10 5Inches of Mercury 205 159 98 28 19 17 9 4

psi 88 69 42 13 10 7 4 2

50 Years Feet of Water 204 159 97 29 22 17 9 4Inches of Mercury 180 140 86 26 20 15 8 4

• Table 9 is extrapolated from critical collapse test data of actual pipe samples• Full Vacuum is 14.7 psi, 34 feet of water or 30 inches of mercury

Note: The values presented in Table 9 represent the safe maximum differential pressures which can beapplied to polyethylene pipe without buckling or collapsing the pipe. These values are calculated usinglower tolerance limits based on extensive long-term differential pressure test data on lengths of pipe.Temperature affects the long and short-term strength of polyethylene pipe. The following multipliers applyto Table 9 for temperature rerating.

TABLE 10: MULITIPLIERS FOR TEMPERATURE RERATING

50°F (10°C) 73.4° (23°C) 100°F (38°C) 120°F (49°C) 140°F (60°C)1.14 1.00 0.79 0.62 0.50

Note: Direct burial or grouting of the pipe provides additional support for the pipe and can increase itsstructural differential-pressure capability by up to four-fold. The degree of increase is difficult to quantify.Structural support is dependent upon installation practices. Caution should be used if designs are basedon this factor.

If these vacuum ratings are exceeded, pipeline collapse may be accelerated. Under excessive vacuum,the mode of failure is not immediate closure or collapse but rather progressive oval deflection. Failure of avacuum pipeline is considered to occur when the maximum pipe diameter in a deflected pipe is 120% ofthe original pipe diameter, (i.e. Dmax = 1.2 x Do)

27

FIGURE 2: RING DEFLECTION OF POLYETHYLENE PIPE

DMAX

Deflected Pipe

DO DMIN

%RingDeflectionD

DMIN

O

= −

×1 100% %Ovality

D

DMAX

MIN

= −

×1 100%

At the deflection limit, the cross-sectional flow area of the pipe is reduced to about 98% of the area ofperfectly round pipe, and the flow is slightly impeded. Ring ovality at this level has been accepted asthe limit. Further deflection beyond this limit occurs rather rapidly, proceeding to full collapse andclosure of the pipeline.

SLIPLINING EXISTING PIPELINES Sliplining is an economical and effective method ofpermanently restoring deteriorated sewer systems. Although a smaller pipe is slipped into an existingmain, the flow properties of polyethylene pipe may restore the capacity of the system while the butt-fused joints eliminate groundwater infiltration. Eliminating infiltration reduces the quantity of sewage tobe transported and treated.

PERFORMANCE CAPABILITY When Driscopipe HDPE pipe is used as a non-pressurized liner, theengineer must design a system that will resist any short-term or long-term external hydrostatic headwithout the benefit of circumferential soil support. The external water table may infiltrate the spacebetween the old sewer and the new liner pipe. The polyethylene liner pipe must be capable ofsupporting this external hydrostatic head.

SLIPLINING CAPACITY Since most sewage flow is gravity flow, the Manning’s formula can beapplied to many sliplining applications. Using the formulae on p. 21 of this manual, a liner size canoften be selected to restore the sewer to its original capacity. A good rule of thumb in sizing the pipeliner is to allow 10% clearance between the existing pipe and the new sliplined pipe (i.e.: ODPolyethylene

= 90% IDSewer).

Using the Manning roughness coefficient for polyethylene, clay tile, and concrete, it can be shown thatfor the same slope, the inside diameter of Driscopipe need be only 82.6% of the ID of the concretepipe and 89.8% of the ID of clay pipe to provide the same flow rate.

Example: A concrete sewer with an ID of 12” has been corroded by the hydrogen sulfideproduced by the sewage. It must be relined. What is the minimum inside diameter requiredto restore full design flow when sliplining with Driscopipe HDPE pipe?

Because the ID of polyethylene pipe needs to be only 82.6% of the ID of the concrete pipe toprovide the same flow, a new liner can be selected as follows:

28

0826 12 9 912. " . "× =One Driscopipe liner that would satisfy this application is 10” DR26 with an ID of 9.924”. Inthis application, the liner would offer greater than 100% of the original flow.

Additional information on design and installation of slip lined systems is available in ASTM F 585,“Practice for Insertion of Flexible PE Pipe into Existing Sewers”, and the Plastics Pipe Institutepublication “Pipeline Rehabilitation with Polyethylene Pipe”.

Note: When sliplining sewers, allow the pipe to normalize to the ground temperature andrecover any imposed stretch (usually 8-10 hours) before cutting the pipe to lengthbetween manholes. If the pipe is not secured at each end, it may contract or shrink intothe existing sewer.

GROUTING Pipe running through the wall of a manhole can be anchored by fusing a side-walledbranch saddle and encasing it into the concrete wall of the manhole. Expandable rubber seals andgrouting have proven successful in sealing an annulus between a casing pipe and polyethylene pipewhen it enters a manhole.

The annulus between the inner polyethylene pipe and the outer pipe is sometimes grouted.Continuous grouting without voids can provide structural support to the liner pipe. If a void exists inthe annular space, the potential structural benefits will be lost. In actual grouting procedures, it isextremely difficult to achieve a void free annulus.

Localized grouting can be used at connections to manholes and to stabilize movement of the linerpipe. Caution must be exercised during the grouting process not to exceed the collapse pressure ofthe polyethylene pipe. Please refer to Table 9 for external pressure capability of unsupported pipe.

In sliplining installations, consideration should be given to:(1) Anchoring the polyethylene pipe within the casing pipe to eliminate expansion and

contraction if such a problem exists.(2) Sealing the annulus to prevent infiltration and/or contamination.

GAS FLOWThe Mueller Formula will calculate the flow capacity of polyethylene pipe carrying a gas.

The Mueller Formula:

Q2826G

P PL

x D0.42512

22 0.575

2.725= −

Where: Q = Gas flow rate, standard cubic feet per hour (SCFH)G = Specific gravity (Air = 1.0; Natural Gas = 0.65)P1 = Inlet pressure, psia (absolute pressure; Pabsolute = Pgauge + Patmospheric)P2 = Outlet pressure, psiaL = Pipeline length, ftD = Inside diameter, in.

Note: Polyethylene is a excellent electrical insulator. Static electric charge generated in the pipe wall dueto gas flow is not readily dissipated. Appropriate safety precautions should be used to prevent accidentaldischarge of static electricity.

Additionally, in gas pipeline applications exposed to the sun, black Driscopipe products may result in atemperature rise of the gaseous product and a subsequent increase in pressure.

29

THERMAL CONSIDERATIONSTests conducted on Driscopipe HDPE pipe have defined its response to temperature within a practicalrange from below freezing to 140o F. This information allows the engineer to evaluate expansion andcontraction over the system’s operating temperature range and to design anchoring when required.

PRESSURE RATINGS Pressure rating is a function of DR and temperature.The pressure rating of PE 3408 resin can be obtained from Table 11. A linearinterpolation may be made within the temperatures shown.

TABLE 11: DRISCOPIPE ® PE 3408 PIPE - PRESSURE RATING (PSI) VS. TEMPERATURE (°F)

Temperature Hydrostatic Design Pipe DR°F Basis, psi 32.5 26 21 19 17 15.5 13.5 11 9 750 1,820 58 73 91 101 114 126 146 182 228 30360 1,730 55 69 87 96 108 119 138 173 216 288

73.4 1,600 51 64 80 89 100 110 128 160 200 26780 1,520 48 61 76 84 95 105 122 152 190 25390 1,390 44 56 70 77 87 96 111 139 174 232

100 1,260 40 50 63 70 79 87 101 126 158 210110 1,130 36 45 57 63 71 78 90 113 141 188120 1,000 32 40 50 56 63 69 80 100 125 167130 900 29 36 45 50 56 62 72 90 113 150140 800 25 32 40 44 50 55 64 80 100 133

TABLE 12: INSTANTANEOUS MODULUS OF ELASTICITY (psi) VS. TEMPERATURE (°F)

140°F 50,000 psi100 °F 100,000 psi73.4°F 130,000 psi50°F 165,000 psi32°F 200,000 psi0°F 260,000 psi

-20°F 300,000 psi

THERMAL CONDUCTIVITY The thermal conductivity of polyethylene is low compared to metals.The coefficient of thermal conductivity is 2.7 BTU in/ ft2 hr °F.

THERMAL EXPANSION AND CONTRACTION All materials expand and contract as a result oftemperature changes. Polyethylene has a higher coefficient of expansion than most other pipingmaterials. The forces generated by thermal stresses are much lower due to polyethylene’s lowermodulus of elasticity and its capability to stress relax. The expansion and contraction characteristicsof polyethylene should be considered in the design and installation of systems.

The linear thermal expansion coefficient for Driscopipe HDPE pipe is 1.2 x 10-4 in./in./°F. Thecircumferential coefficient of expansion is approximately half of the linear expansion coefficient, (i.e.0.6 x 10-4 in./in./°F).

30

The amount of linear expansion or contraction for an unrestrained polyethylene pipe can be calculatedfrom the following equation:

Where: ∆L = Theoretical length change, in.α = Coefficient of linear expansion, 1.2 x 10-4 in./in./°FT2 = Final temperature, °FT1 = Initial Temperature, °FL = Length of pipe, in. at T1

THERMAL STRESS RELAXATION When the temperature of a Driscopipe system changes,internal stresses develop as the pipe expands or contracts. This does not adversely affect oroverstress the pipe. Polyethylene is a viscoelastic material and will relieve stresses by slightlyrealigning its molecular structure until equilibrium is achieved. This is a valuable engineering propertywhich dissipates a major portion of the stress developed as the pipe tries to expand or contract.

The engineering formulas used to calculate forces resulting from expansion or contraction assumeinstantaneous temperature change. It is physically impossible to change the temperature of an objectinstantly. In laboratory experiments structured to create a near “instantaneous” temperature changeon the pipe, the thermal stress has been measured and found to be about half the theoretical,calculated value. When the temperature change occurs over an extended period of time, the thermalstress is further reduced as stress relaxation occurs. Typically, Driscopipe systems are designedusing one half the calculated tensile stress due to an “instantaneous” temperature change.

THERMAL CONSIDERATIONS IN SUPPORTED PIPELINES If practical, install the pipewhen its temperature is near the maximum system operating temperature. As the pipe cools, tensilestress will develop and keep it straight between supports. When the pipe warms to its installationtemperature, it returns to its installation condition and straightness. In this manner, sag betweensupports is minimized.

THERMAL CONSIDERATIONS IN OVERLAND PIPELINES By installing overland pipelinesin a slightly snaked pattern, changes in the pipe’s length can be controlled by lateral deflection. As thepipeline warms, the “S” configuration becomes slightly greater. As the pipe cools, the pipelinebecomes straighter. Surface lines that are continuously operated full of fluid normally experiencesmall temperature variations and are easy to control. The weight of the fluid also increasesfriction between the pipe and the ground and therefore reduces deflection.

It may be necessary to anchor the line at intervals to direct and limit the deflection to selectedlocations. In extreme cases, all deflection may occur in one area where friction is low. This conditionis most likely to occur with empty lines or where large, sudden operating temperature changes occur.

LATERAL DEFLECTION DUE TO THERMAL MOVEMENT The following formulae willallow the designer to calculate lateral deflection of the pipeline and anchor point spacing.

∆ ∆Y L T= 0 50. α

LY

T=

∆∆050. α

LD T

=96αε

∆

∆L T T L= −α ( )2 1

31

Where: ∆Y = Lateral deflection, in.L = Length of pipe between anchors, in.α = Coefficient of thermal expansion, in./in./°F

∆T = Change in temperature, oFD = Pipe outside diameter, in.ε = Tangential strain, in./in.

FIGURE 3: LATERAL DEFLECTION DUE TO THERMAL MOVEMENT IN OVERLANDPIPELINES

For any set of thermal conditions, an increase in anchor spacing will increase deflection, and viceversa. Increasing anchor spacing, L, to the maximum will reduce the number of anchor points neededbut may increase wear on the pipe from movement and may increase the possibility of kinking the lineif lateral movement does not occur uniformly.

One practical approach is to calculate anchor spacing by limiting strain, ε, in the pipe wall between 1%and 5%. The spacing at 5% strain will give the minimum distance between anchor points at themaximum allowable strain (εmax). The spacing should be as large as possible considering otherfactors such as available right-of-way and slope of the ground. Higher values for L mean less strainand fewer anchor points.

Example: A pipeline installed on top of the ground in a straight condition and anchored at 50 footintervals undergoes an increase in temperature of 50°F.

∆Y ft in ft F= × × ×50 12 050 00012 50./ . .

∆Y in= 33 .

THERMAL CONSIDERATIONS IN BURIED PIPELINES In direct buried installations, soilfriction will normally restrain pipe movement caused by seasonal temperature changes. Anchorrequirements are minimized as stress relaxation occurs in the pipe. In some instances, concretecollars are used to transfer the thermal force into the soil around the pipe. The force in the pipe mustbe effectively transferred into the concrete collar. This is typically done by fusing branch saddles or a“waterstop” to the pipe and embedding the waterstop into the concrete collar.

The final tie-ins on a system should be made as close to operating temperature as practical. Wheninstalling polyethylene pipe that is warmer than the soil, a slightly longer length may be required tocompensate for contraction of the pipe as it cools to ground temperature. The snaking in the trenchwhich naturally occurs with pipe diameters 4" and below is normally sufficient to compensate for

32

thermal contraction. During a winter installation, the exact length of pipe should be used. Pipe whichis too short or not aligned must not be drawn up by the bolts of a flanged connection. Overstressingthe flange adapter may result in failure.

When the backfill is soft or becomes fluid, as in marshes or river bottoms, the pipe movement may notbe restrained by the backfill. Under this condition, the stress in the pipe is transmitted to the endconnections. This can damage weak connections. If this possibility exists, anchors should beinstalled just ahead of the termination to isolate and protect the connection.

The calculated force due to temperature change is the product of the stress in the pipe wall and thecross sectional area of the pipe wall. The length of pipe required to anchor the pipeline against thiscalculated force depends on the circumference of the pipe, the average contact pressure between thesoil and the pipe, and the coefficient of friction between the soil backfill and the pipe.

The stress and force that develop due to temperature change in a restrained pipeline are independentof the length and the burial conditions of the pipe. If pipe movement at the end sections cannot betolerated, the pipe must be anchored. Properly designed restraints transfer the forces into the soil. Ifthe pipe is not anchored to resist movement, the end sections will expand or contract as thetemperature changes. This change in length will extend into the burial trench until the frictionalresistance of the backfill is equal to the thermal force. These movements must be considered in thedesign of such physical features as connections to pumps, catch basins, sewer manholes, etc.

THERMAL CONSIDERATIONS IN MARINE PIPELINES In most marine applications, thewater temperature is relatively constant. Seasonal changes in water temperature occur over severalmonths. Thermal stress in marine applications is normally controlled by stress relaxation and verticaldeflection between anchor points.

TRANSITION CONNECTIONS If the pipe is not anchored at the ends to resist movement, a fewfeet at each end may expand or contract as the temperature changes. This zone will extend into theburial trench to a point at which the frictional resistance of the backfill is equal to the thermal force.These movements must be considered in the design. Anchoring should be provided when the pipemust be connected to a tank, manhole, valve, etc. Figure 16 illustrates several anchor systems for typicaltypical end connections.

A polyethylene pipeline is also subject to circumferential expansion and contraction. The designermay need to consider this in certain applications.

The following example may be helpful.

EXAMPLE: 4” DR 15.5 Driscopipe PE 3408 pipe is buried five feet deep in dense sandy soil with ahigh water table. The ground temperature is 60o F. Occasionally, it is used to carry 40o F water. Theline runs straight and is 1000 feet long. Calculate the following:

• The temperature change• The theoretical strain• The theoretical length change• The instantaneous tensile stress in the pipe wall• The tensile force• Design a collar to isolate the terminal connection from the effects of thermal contraction.

DATA: Pipe Outside Diameter D = 4.5”Pipe Wall Cross-Sectional Area A = 3.84 in.2

Linear Coefficient of Thermal Expansion α = 1.2x10-4 in./in./°F

Instantaneous Modulus of Elasticity E = 180,000 psi @ 40°FTemperature Change ∆T = 20o F

33

Soil/HDPE Pipe Coefficient of Friction µ = 0.10Length of Straight Run L = 1000 FeetSoil Density γ = 130 lbs/ft3

Depth of Burial h = 5 Feet

CALCULATIONS:

Thermal Strain, ε: ε = (α) (∆T) = (1. 2 x10-4 in./in./oF)(20o F) = 0.0024 in./in.

Theoretical-Instantaneous Unrestrained Contraction, ∆L: ∆L = (ε)L∆L = (0.0024 in./in.)(1000 ft)(12 in./ ft) = 28.8 in.

Note: Since the soil restrains the pipe, it will not change length but will insteaddevelop tensile stress due to contraction.

Theoretical Tensile Stress, σ:

E =σε

σ ε= ×E = (180,000 psi) x (0.0024 in./in.) = 432 psi

Note: The instantaneous modulus of elasticity was taken at the lower temperature (i.e. E 40°

is approximately 180,000); Refer to Table 12.

Actual Tensile Stress, σA: σA = 432/ 2 = 216 psi tensile stress (“Thermal Stress Relaxation”, p.30)

Actual Tensile Force, F: F = (σA)(A)

F = (216 psi) (3.84 in.2)

F = 829.4 lbs (Tensile)

Soil Frictional Resistance, f: f = µN

Where: Soil pressure = γh = (130 lbs/ft3)(5 ft) = 650 psf = 4.5 psi

Normal Force (N) = Force due to soil pressure on circumference of pipering one inch wide.

N =(πD) x (1”ring) x (soil pressure)N = (π x 4.5”) x (1”) x (4.5 psi)N = (14.14 in.2) x (4.5 psi)N = 63.62 lbs

f = µN = (0.10)(63.62 lbs)

f = 6.362 lbs (per inch of pipe due to soil friction)

Beyond 130.4 inches (10.86 ft), the soil friction will overcome the tensile force developed bythermal contraction of the pipeline. This is calculated by dividing the tensile force in the pipe bythe frictional resistance of the soil (i.e. 829.4 lbs / 6.362 lbs per in of pipe = 130 Inches).

34

Theoretical Movement of Unrestrained Ends, ∆L:

∆L = (Length of unrestrained zone)(ε)∆L = (130 in.)(0.0024 in./in.) = .312 in.

Design of a Restraining Collar:

Movement at the ends of the pipe can be restrained by anchoring. In undergroundinstallations, a concrete thrust block is often used to transfer the tensile loading in the pipeinto the surrounding soil. The tensile load in the pipe must first be transferred into theconcrete. Since the concrete will not “grip” the pipe’s smooth surface, a branch saddle orwaterstop fitting is fused to the pipe and embedded in the concrete. This transfers theforces by shear into the concrete and the surrounding soil. Driscopipe HDPE pipe has ashear strength of approximately 1,500 psi. The concrete thrust block is sized based onthe compressive strength of the soil.

Assume a square collar 12 inches x 12 inches and 6 inches wide. The net surface bearingarea of the collar is:

Net Area of Collar = (12” x 12”) - (π x (4.52/4)) = 144 in.2 - 15.9 in.2 = 128.1in.2

The compressive stress on the soil due to load transfer by collar face: S = F / AS = 829.4 lbs ÷ 128 in.2 = 6.5 psi

EXAMPLE DESIGN SUMMARY: Under a 20o F temperature change, a 4” DR 15.5 pipeline 1000ft long buried five feet deep will try to change length 0.312” at each end. The pipe is restrained bysoil friction from further contraction. A concrete collar with a square face of 12” x 12” will absorbthe tensile force of 827.3 lbs due to thermal contraction, and distribute it into the soil at acompressive soil stress of 6.5 psi.

35

BURIAL DESIGNBURIED PIPELINES Buried pipelines are subject to external loads. The effect of external pressure

on Driscopipe pipelines is more complex than the effect of internal pressure only. For designpurposes, a distinction is usually made between rigid and flexible pipes. A rigid pipeline (such asconcrete) is considered to be the total structure and must be designed to support all external loads aswell as internal pressure. Because polyethylene pipe is flexible, it is considered to be only onecomponent of the “pipe-soil” system.

In a buried situation, the DR of the pipe and the strength of the soil envelope must be specified tokeep the three burial design parameters (wall crushing, wall buckling and ring deflection) withinacceptable limits. Correct design is based on two key parameters. The first is matching the properwall thickness to the external soil pressure. Secondly, correct design calls for an analysis of howDriscopipe HDPE pipe and the surrounding soil accept the backfill loading and transfer it to theundisturbed walls of the trench.

BURIAL DESIGN CONSIDERATIONS When polyethylene pipe is buried, the soil surroundingthe pipe will compress or deflect slightly under both static and dynamic loads. These loads include theweight of the backfill above the pipe, the weight of the water table saturating the soil, vehicular traffic,nearby structures, or any combination of these loads. In a flexible “pipe-soil” system, the pipedeflection is assumed to be the same as the soil deflection.

After a pipe is laid in the trench, the backfill is placed in layers to an elevation above the top of thepipe. It is compacted to a specified Proctor density. As additional layers are placed, the weight of thesoil over the primary, compacted backfill increases. This slightly compresses the soil around the pipe.Since soil is not an elastic material, the compression, i.e. strain, is permanent. In its denser state, thesoil develops increased resistance to the vertical soil pressure until it reaches static equilibriumwithout further compression or strain.

LIMITS OF BURIED PIPES DUE TO EXTERNAL SOIL PRESSUREThe ring deflection of Driscopipe HDPE pipe can be calculated by using the properties of the pipe andthe measured compressibility of the soil. As the pipe deflects with the soil, it forms a very slight ellipseby decreasing in the vertical diameter an amount, ∆Y, and by increasing in the horizontal diameter analmost equal (but slightly less) amount, ∆X. The horizontal diametrical increase further compacts thefill at the sides of the pipe, developing lateral support. The vertical decrease in diameter relieves thepipe of vertical soil pressure concentrations and forces the soil to support the major share of thevertical load by arching action over the pipe.

Deformation of buried flexible pipe becomes critical when the pipe reaches that point of ring deflectionbeyond which it can no longer resist any increase in soil loading. By limiting ring deflection throughproper soil compaction, the loading over a pipe is distributed through the soil and across the soil archaround the pipe.

The Soil Modulus, E’, is the ratio of soil pressure (stress) to soil deflection (strain) at a given soilcompaction. Refer to Table 13 for values of E’.

36

TABLE 13: VALUE OF E’ BASED ON SOIL TYPE (ASTM D2321)AND DEGREE OF COMPACTION

E’ (psi) for Degree of Compaction (Proctor Density, %)

Soil Type of InitialBackfill Material

Loose 70%

Slight( 70 - 85%)

Moderate( 85- 95%)

High> 95%

I Manufactured angular,granular materials

(Crushed Stone, or rock,broken coral, cinders,

etc.)

1,000 3,000 3,000 3,000

II Coarse grained soilswith little or no fines

NotRecommended

1,000 2,000 3,000

III Coarse grained soilswith fines

NotRecommended

NotRecommended

1,000 2,000

IV Fine Grained Soils NotRecommended

NotRecommended

NotRecommended

NotRecommended

V Organic Soils(Peat, Muck, Clay, etc.)

NotRecommended

NotRecommended

NotRecommended

NotRecommended

Note: This summary of ASTM D 2321 is provided for the design engineer’s convenience. This specification should be reviewed in detail before specifying burial conditions.

MINIMUM COVER There are no firm rules regarding minimum burial depth. The variables changefor each installation, and the designer should check each design for wall crushing, wall buckling, andring deflection. However, the following guidelines may be helpful.

• Consider a burial depth below the local frost line.• Where there will be no overland traffic, the designer may wish to consider a cover of

18” or one diameter, whichever is greater.• Where truck traffic may be expected, the designer may wish to consider a burial

depth of 36” or one diameter, whichever is greater.• Where heavy off-the-road truck or locomotive traffic is expected, the designer may

wish to consider a minimum cover of 5 feet or more.

CALCULATION OF TOTAL SOIL PRESSURE BY COMPONENTS Proper design of thepolyethylene “pipe-soil” system balances the response of the pipe and surrounding soil against thetotal external soil pressure. Burial design by wall crushing, wall buckling, and ring deflection requirethe calculation of the total soil pressure, PT, at the top of the pipe. There are many sources of soilpressure above the pipe. It is helpful to examine the total soil pressure as the sum of its components.

37

The total external soil pressure at the top of the pipe includes the sum of:

PT = PS + PL + PI

Where: PS = Total “Static Load” pressure or dead load pressure.PL = Total “Live Load” pressure.PI = Total effective external pressure due to negative internal

operating pressure (vacuum).

Each of these soil pressure components is discussed and examples are calculated for use in a typicaldesign problem.

TOTAL STATIC LOAD PRESSURE, P S There are three sources of static load pressure. The totalstatic load pressure is the sum of these components:

PS = PDE + PWE + PB

Where: PDE = Static load pressure of dry or slightly moist earthPWE = Static load pressure of wet, saturated soil under the maximum water table.PB = Static load pressure due to stationary surface structures such as buildings

or foundations.

DRY SOIL PRESSURE, PDE The weight of dry soil is approximately 100-120 pounds per cubic foot(pcf). Every foot of “dry” soil above the pipe exerts a pressure of 100 to 120 pounds per square footon the crown of the pipe. The dry soil component of the total static load pressure, PDE, is the productof the dry soil density and the depth of the soil (in feet) from the ground surface to the top of the watertable over the pipe.

WATER SATURATED SOIL PRESSURE, PWE The water saturated soil component of the staticload pressure is the product of the wet soil density, approximately 120-140 pcf, and the height of thewet soil above the pipe.

STATIC STRUCTURE SOIL PRESSURE, PB In some applications, the pipe may be installed underor near a building or other structure. If the structure is located directly over the pipeline, the pressuredue to the weight of the structure is more concentrated and intense than if the structure is located atsome distance away. The distribution of vertical pressure into the soil below a static load isrepresented by a bell or bulb shaped surface. Refer to Figure 4. The maximum pressure exerted bythe static structure is located at the centerline of the bulb. The pressure decreases downwards in alldirections and outwards from the center. The external soil pressure which a ground structure willexert on HDPE pipe is greater when the pipe is buried near the structure and fairly shallow. Theexternal soil pressure is less when the pipe is buried deeper or farther away from the static structure.

The Boussinesq theory is recommended for determining the pressure from a concentrated load. Bythis theory, the load at the top of the pipe caused by a superimposed static load is evaluated asfollows:

PWZ

RB =3

2

3

5πWhere: PB = Static structure soil pressure, lb/ft2

W = Superimposed surface load, lbZ = Vertical distance from the point of load to the top of the pipe, ftR = Straight line distance from point of load to the top of the pipe, ft

R X Y Z= + +2 2 2

38

X and Y are horizontal distances at 90o to each other from the point of load to the top of the pipe infeet.

Using this theory, a simplified chart can be used to show the underground pressure distributioncaused by a 1000 lb superimposed surface load (Figure 4). The underground pressure for othersuperimposed surface loads can be calculated by multiplying the chart value by the load ratio per theexample in this section.

If the pressure on the pipe is caused by a uniformly distributed surface load such as a foundation,spread footing, or bearing pad, the soil pressure on the pipe can be determined by dividing the loadedarea into a group of smaller individual areas. The load for each incremental area is calculated andadded to obtain the total soil pressure on the pipe caused by the foundation. This technique isillustrated in the following example. A further discussion of this method is found in Soil Mechanics inEngineering Practice by Terzaghi and Peck.

FIGURE 4: UNIT UNDERGROUND SOIL PRESSURE EXERTED BY 1000 lb LOAD

Example: A 24” diameter sewer line is to be laid through a plant area with the top of the pipe being 10feet below grade. The seasonal water table rises to a maximum height of 7 ft below the ground surface(i.e. 3 feet above the pipe). At one point, the centerline of the pipe is buried four feet from and parallel tothe long side of an equipment foundation which is 6 ft wide and 10 ft long and has a load bearing of 3000psf at a depth of 3 feet below grade. Determine the total static load pressure on the pipe at point ‘A’.Point ‘A’ is located on the pipe directly across from the midline of the static structure (i.e. 5 feet).

P psfB = ×72 0001 000

2 0,

,.

P psf psiB = =144 1

Example: Find static soil pressure of a 72,000 lbweight on a pipeline buried 10 feet deep and 6.5feet away.

39

Refer to the diagram below.

Given: Density of dry soil = 100 lbs/ft3

Density of saturated soil = 130 lbs/ft3

Depth of burial, H = 10 ftHeight of saturated soil level above the pipe, h, = 3 ft Height of dry soiI above the pipe, (H - h) = 7 ftFoundation bearing load = 3000 psf @ 3 ft. deep

Diagrams:

Formula: PS = PDE + PWE + PB

Where: ( )( )P H hDE WE= − ρ

( )( )P hWE DE= ρ

PWZ

RBO

i

= ∑ 3

2

3

5π Z = Vertical Height

R X Y Z= + +2 2 2

Note: For a simplified calculation of PB, use Figure 4.

40

Calculations: PDE = (10ft - 3 ft)(100 pcf) = 700 psfPWE = (3 ft)(130 pcf) = 390 psfPB = 300 psf (see Table 14)

Summary: PS = PDE + PWE + PB

Ps = 700 + 390 + 300 = 1390 psfPs = 9.65 psi at point ‘A’ on the pipeThe load area of the static structure is divided into fifteen squares. Eachsquare is 2 ft x 2 ft for a total area of 60 ft2. The total weight of eachsquare is the equivalent of 12,000 lbs (4 ft2 x 3000 psf = 12,000 lb).

TABLE 14: DETERMINING SOIL PRESSURE FROM A STATIC LOAD

Pressure (From Fig.4) 12000# Vertical Horizontal Per Load

Square Weight Depth Distance 1000# Load Per Square

1-1 12,000 7 ft. 6.4 2.1 psf x 12 = 25.2 psf 1-2 12,000 7 ft. 8.1 1.2 psf x 12 = 14.4 psf 1-3 12,000 7 ft. 9.8 0.6 psf x 12 = 7.2 psf 2-1 12,000 7 ft. 5.4 3.0 psf x 12 = 36.0 psf 2-2 12,000 7 ft. 7.3 1.5 psf x 12 = 18.0 psf 2-3 12,000 7 ft. 9.2 0.8 psf x 12 = 9.6 psf 3-1 12,000 7 ft. 5.0 4.0 psf x 12 = 48.0 psf 3-2 12,000 7 ft. 7.0 1.7 psf x 12 = 20.4 psf 3-3 12,000 7 ft. 9.0 0.9 psf x 12 = 10.8 psf 4-1 12,000 7 ft. 5.4 3.0 psf x 12 = 36.0 psf 4-2 12,000 7 ft. 7.3 1.5 psf x 12 = 18.0 psf 4-3 12,000 7 ft. 9.2 0.8 psf x 12 = 9.6 psf 5-1 12,000 7 ft. 6.4 2.1 psf x 12 = 25.2 psf 5-2 12,000 7 ft. 8.1 1.2 psf x 12 = 14.4 psf 5-3 12,000 7 ft. 9.8 0.6 psf x 12 = 7.2 psf

PB = 300 psf

TOTAL LIVE LOAD PRESSURE, P L Traffic operating over or near a buried pipelines causes theearth to move slightly under its weight. Live loads are also evaluated by the Boussinesq theory. Thewheel or axle weight should be increased by 50% to provide a pipe design with extra strength andendurance against the impact of these dynamic forces. The load at the top of the pipe caused by asuperimposed dynamic load at a given point is evaluated by:

PWZ

RB =3

2

3

5π

Where: W = 1.5 x Superimposed surface load, lbZ = Vertical distance from the point of load to the top of the pipe, ftR = Straight line distance from point of load

to the top of the pipe, ft

R X Y Z2 2 2= + +

41

Where X and Y = Horizontal distances at 90o to each other from point of load to the top of the pipe infeet.

Unit underground pressures caused by a 1,000 pound superimposed static load are shown in Figure4. Unit pressures for superimposed live loads can be obtained by multiplying the values in Figure 4 by1.5. The readjusted unit pressure is then multiplied by the load ratio. The load ratio was twelve in theprevious example.

Figure 5, H20 Live Loading, and Figure 6, Cooper E-80 Live Loading, summarize the total pressuredue to the weight of the soil and the weight of the rolling vehicle. An allowance for impact is includedin each of these figures.

Beyond an optimum depth, the total pressure on the pipe increases primarily as a result of soilpressure. This effect can be seen in Figures 5 and 6. At shallower depths, the load intensifiesbecause the pipe is nearer to the rolling equipment, and the live load is not as well distributed to thesoil.

If the live load pressure exceeds the capability of a specific DR pipe for a specific traffic situation, thedesigner may want to consider methods to protect the pipeline.

FIGURE 5: H20 HIGHWAY LOADING

Note: The H20 live load assumes two16,000 lb. concentrated loads applied totwo 18” x 20” areas, one located over thepoint in question, and the other located ata distance of 72” away. In this manner, atruckload of 20 tons is simulated.

Source: American Iron and Steel Institute,Washington, DC

42

FIGURE 6: COOPER E-80 LIVE LOADING

APPARENT EXTERNAL PRESSURE DUE TO INTERNAL VACUUM, P I Vacuum generates acompressive hoop stress in the wall of a pipe and acts to collapse the pipeline. Under vacuumconditions, the value of PI is positive. PI is added to the other two external pressure components, PS

and PL, to obtain the total external pressure, PT, acting on the pipe. An internal vacuum generatespressure equal to the absolute value of the vacuum. The maximum apparent external pressure due toa vacuum inside the pipe is 14.7 psi (2,117 psf).

BURIAL DESIGN GUIDELINES The design engineer must select the proper pipe DR and specifythe backfill conditions to obtain the desired performance of the “pipe-soil” system.

DESIGN BY WALL CRUSHING Wall crushing occurs when external vertical pressure causes thecompressive stress in the pipe wall to exceed the long-term compressive strength of the pipe material.To design for wall crushing, the following check should be made:

( )S

SDRPA T=

− 1

2

Where: SA = Actual compressive stress, psi SDR = Standard Dimension Ratio

PT = Total external pressure on the top of the pipe, psi

Safety Factor = 1500 psi /SA (where 1500 psi is the compressive yield strength of Driscopipe HDPE pipe)

DESIGN BY WALL BUCKLING Local wall buckling is a longitudinal wrinkling of the pipe wall.Buckling can occur over the long term in non-pressurized pipe if the total external soil pressure, PT,exceeds the pipe-soil system’s critical buckling pressure, Pcb . Although wall buckling is seldom thelimiting factor in the design of a Driscopipe system, a check of non-pressurized pipelines can be madeaccording to the following steps to insure PT < Pcb . All pipe diameters with the same DR in the sameburial situation have the same critical collapse and critical buckling endurance.

Note: Cooper E-80 live load assumes 80,000pounds applied to three 2’ x 8’ areas on 5’centers such as might be encountered throughlive loading from a locomotive with three 80,000pound axle loads.

Source: American Iron and Steel Institute,Washington, DC

43

1. Calculate or estimate the total soil pressure, PT, at the top of the pipe.

2. Calculate the stress, Sa, in the pipe wall:

( )S

SDR Pa

T=− 1

2

3. Based upon the stress Sa and the estimated time duration of non-pressurization, find thevalue of the pipe’s modulus of elasticity, E, in psi (approximate value for E is 35,000 psi).

4. Calculate the pipes hydrostatic, critical-collapse differential pressure, Pc

( ) ( )

( )Pc

E t D DMIN DMAX=

−

23 3

12

/

µ or

( )P

E

SDRc =2 32

3

.

Where: (DMIN/DMAX) = 0.95µ = Poission’s Ratio = 0.45 for polyethylene pipeE = stress and time dependent tensile modulus of elasticity, psiE = 35,000 psi (approximate)D = Outside Diameter, in.

t = thickness, in.

5 Calculate the soil modulus, E’, by plotting the total external soil pressure, PT, against aspecified soil density to derive the soil strain as shown in the example problem below Figure7.

6. Calculate the critical buckling pressure at the top of the pipe by the formula:

P E Pcb c= 08. ( ' )( )

Where: Pcb = Critical buckling soil pressure at the top of the pipe, psiE’ = Soil Modulus, psiPc = Hydrostatic critical-collapse differential pressure, psi

7. Calculate the Safety Factor: SF = Pcb / PT .

8. The above procedures can be reversed to calculate the minimum pipe DR required for agiven soil pressure and an estimated soil density.

In a direct burial pressurized pipeline, the internal pressure is usually great enough to exceed theexternal critical-buckling soil pressure. When a pressurized line is to be shut down for a period, wallbuckling should be examined.

44

FIGURE 7: PLOT OF VERTICAL STRESS-STRAIN DATA

FOR TYPCIAL TRENCH BACKFILL (EXCEPT CLAY) FROM ACTUAL TESTS

Example:Find: E’ @ 2000 psf and 80% densityFormula: E’ = PT/εS

Calculations: E’ = 2000 psf / (0.018 * 144) = 771 psi

Design by Ring Deflection Ring deflection, by definition, is the ratio of the vertical change indiameter to the pipe’s original diameter. It is often expressed as a percentage.

Driscopipe HDPE pipe is designed to be “flexible”. This assumes the pipe will deflect the same as thevertical compression of the soil around it. Design by ring deflection matches the ability of the pipe toaccommodate, without structural distress, the vertical compression of the surrounding soil. Design byring deflection calculates the vertical soil strain and compares it to the allowable ring deflection of thepipe.

Note: The curves shown on this chart are sample curves for a granular soil.If other types of soil are used for backfill such as clay or clay loam, curvesshould be developed from laboratory test data for the material used. Soilpressures greater than 4000 psf may be extrapolated with the slope of thecurve or curves can be generated by testing at higher soil pressures.Probable error of curves is about half the distance between adjacent lines.

45

TABLE 15: ALLOWABLE RING DEFLECTION OF DRISCOPIPE ®

POLYETHYLENE PIPE BASED UPON DR

DR Allowable Ring Deflection

32.5 8.1%

26 6.5%

21 5.2%

19 4.7%

17 4.2%

15.5 3.9%

13.5 3.4%

11 2.7%

The allowable ring deflection of polyethylene pipe is limited to create no more than 1 to 1.5%tangential strain in the outer surface of the pipe wall. As the wall of a pipe becomes thicker (a “lower”DR value), the distance from the neutral axis to the outer surface increases. As a result, lessdeflection is required to create the allowable tangential strain. Deflection of the pipe-soil system iscontrolled by proper specification of the backfill compaction.

FIGURE 8: CALCULATING RING DEFLECTION

Dmax

DminDo

The percentage ring deflection based upon strain for a given DR pipe can be calculated as follows:

( )( )( )∆Y

DSDR= 0 25. ε

% minRingDeflectionD

Do

= −

×1 100%

46

Where: ∆Y = Vertical deflection, in.D = Pipe OD, in.ε = Tangential strain in the surface of the pipe ring, in./in.SDR = Standard Dimension Ratio

Driscopipe recommends limiting tangential surface strain to 0.01. This value is based upon thefollowing criteria:

• Most of the deflection of a flexible pipe occurs within a few days after final backfillis completed. Development of a soil arch over the pipe relieves the pipe of muchof the vertical soil load by the arching action of the soil envelope and by thedevelopment of soil restraint at the sides of the pipe.

• An allowable strain value of 0.01 will allow for reasonable additional deflection dueto disturbance of the backfill by earthquake, fluctuations of the water table, etc.

• An allowable design strain value of 0.01 allows for the normal deviation oftemperature encountered during installation.

In summary, a soil density can be specified for the bedding and initial backfill so that total soilpressure at the top of the pipe, PT, will not cause a given DR pipe to exceed its maximum allowablering deflection.

47

DRISCOPIPE®

SYSTEMS INSTALLATIONDriscopipe products have been installed in many applications above and below ground. Polyethylenepipe has been used to cross land, lakes, deserts, bogs, and arctic tundra. Each installation requiresthorough consideration of the environment in which the pipe is being installed.

Typical pipe installations can be categorized as one of seven types. The following pages discussdesign details for each type of installation.

TYPE 1: Supported or Suspended Pipelines TYPE 5: Marsh PipelinesTYPE 2: Overland Pipelines TYPE 6: Sliplined PipelinesTYPE 3: Marine Pipelines TYPE 7: Buried PipelinesTYPE 4: Water Surface Pipelines

SUPPORTED OR SUSPENDED PIPELINES

Horizontally supported pipelines are affected by the weight of the pipe and its contents betweensupports. When the sag or deflection between supports is minimized, the stress in the pipe wall canbe controlled. Supports should be spaced to limit the mid-span deflection to about ¼” using a simple,continuous beam analysis.

Supports should cradle the pipe for at least 4” or 1.5 times the pipe diameter, whichever is greater. Aminimum of 120o of the pipe’s circumference should be supported. The supports should be free ofsharp edges.

Often, supported pipelines are installed outdoors. These installations are exposed to temperaturechanges due to weather. If possible, a supported or suspended pipeline should be installed as nearits maximum operating temperature as practical (or in the hottest weather).

When a supported system is warmer than its installation temperature, the pipe will expand. As thepipe increases in length, lateral deflection or “snaking” will occur between restraints. The total amountof expansion that will occur depends on the pipe’s length and the temperature increase above thesystem’s installation temperature. While the total amount of expansion in a pipe cannot be changed,the designer can limit the deflection in a section of the pipe by selecting appropriate anchoring points.

The pipe must be restrained at all fittings and can be restrained at each support. Clampingthe pipe at each support is recommended to limit deflections due to expansion. If the supportis designed as an anchor point, it must be capable of restraining the pipe. If the pipeline isdesigned to move during expansion, the supports should provide a guide without restraint inthe direction of movement.

PIPE SUPPORT SPACING Figures 9 through 13 give the required design support spacing forvarious DRs and pipe diameters. The distance between supports is based upon a continuous beamanalysis and a mid-span deflection of 0.25” when the pipe is filled with water.

48

Figure 9: Pipe Support Spacing for DR32.5 Figure 10: Pipe Support Spacing for DR26

Figure 11: Pipe Support Spacing for DR17 Figure 12: Pipe Support Spacing for DR11

Figure 13: Pipe Support Spacing for DR9

49

There are some additional recommendations concerning support spacing for polyethylene pipe. If anoperating or environmental temperature is expected to be 10° F higher than the installationtemperature, continuous support is recommended to control thermal expansion and prevent excessivedroop. When operating temperatures over 100°F are expected and there is a possibility for rapidtemperature change, the next lower DR pipe at the DR 32.5 spacing can be used. For slurryapplications, multiply spacing by 0.90. Proper anchoring is required at entry and discharge ends ofthe pipeline. Vertical piping should be supported at its base and spring hangers or collars used at 12ft vertical intervals. Avoid expansion loops and design the entire pipeline to take care of its ownexpansion by following proper support spacing and mounting practices.

OVERLAND PIPELINESBlack Driscopipe HDPE pipe resists damage from ultra-violet radiation. Colors other than black tendto deteriorate under constant exposure to the sun and should not be installed in above groundapplications.

Generally, Driscopipe products are installed below ground. However, there are many situations inwhich above ground piping has advantages. Some advantages are as follows:

• Slurry or mine tailings lines which are often relocated and can be rotated to distributewear in the pipe.

• The toughness and flexibility of polyethylene often allows installation through marshesand bogs, over frozen areas, and across other harsh environmental conditions.

• Installations over solid rock or across water are sometimes the most economicalmethods of installation.

• Driscopipe polyethylene pipe is lightweight and ease of assembly results in immediateavailability of a temporary above ground pipeline.

Above ground pipelines are exposed to environmental temperature changes. The pipeline will expandand contract. It will want to “snake” or roll slightly. Allowances should be made for thermal expansion.Polyethylene pipe should be anchored at predetermined intervals to limit movement.

Another method of controlling movement due to thermal expansion/contraction is to allow the pipelineto move freely between two rows of pylons set in the earth. One row is installed on each side of thepipeline. Some pipelines have been installed overland in shallow trenches to limit movement. Whena significant slope is encountered, anchors or trenches are recommended. Anchors, pylons, andtrenches minimize the possibility of the pipeline moving down the slope.

HOT CLIMATES Where possible, the line should be positioned to take advantage of maximumshading from the sun’s direct rays. Thermal expansion may also be minimized if fluid flow can bemaintained at all times or, at least, during the hottest portion of the thermal cycle.

COLD CLIMATES A flame cannot be used to thaw a frozen polyethylene pipe. Other methodsmust be used. Driscopipe products can be heat traced, but the temperature of the tape should belimited to 140oF. Heat tracing tapes which self limit their temperature are preferred. When heattracing is used on polyethylene pipe, the system design temperature must be based on thetemperature of the pipe wall exposed to the tape.

Where freezing occurs in overland applications, precautions should be taken against plugging thepipeline. Constant flow will reduce the chances of freezing. In addition, provisions to drain the pipemay be included in the design.

Freezing will not cause the pipe to burst. The pipe will expand with the expanding fluid. When thewater is thawed, the pipe will return to its original dimensions unharmed.

50

MARINE PIPELINESHDPE pipe can be buried, rested on the bottom, or floated on the water’s surface. The primary designcriteria for submerged and weighted pipelines are (a) the critical collapse pressure for empty orpartially full pipelines, (b) weight of the concrete anchor, and (c) spacing of the concrete anchors.Even though a marine pipeline is sometimes buried in an underwater trench, any support that thepipeline receives from the backfill material is usually ignored for design purposes.

For marine applications, the ballast weights can be precast concrete or cast at the job site. Ballastweights can be designed to hold the pipe away from the bottom using weights as legs or placed in atrench or directly on the bottom. For pipe larger than 12”, it is advisable to use weights withreinforcing steel for added strength. It is further recommended that one turn of rubber gasket materialor 2 to 3 turns of 5 to 10 mil polyethylene sheet be wrapped around the pipe and under the weight toact as a cushion and prevent damage to the pipe.

CRITICAL COLLAPSE PRESSURE A marine pipeline does not receive structural supportfrom the surrounding water. Unless properly designed, an empty or partially filled pipe is subject tocollapse. A marine pipeline that is full of water at all times minimizes the potential for collapsebecause the internal pressure will be similar to the external pressure at any depth of water. Refer toTables 9 and 10 for allowable differential pressure ratings of various DR pipes

ANCHOR WEIGHTS The dry land weight of the concrete anchors, WtConcrete, can be calculatedfrom the following equation. The weight of concrete varies between 140 - 155 pounds per cubic foot.The ‘K’ value is an anchor constant. Neutral buoyancy is achieved when K = 1.0. To adequatelyanchor a pipeline in lakes, ponds, and streams, a ‘K’ value of 1.3 should be used. Where current ortides are encountered, the designer may want to increase the ‘K’ value to nearly 1.5 depending upondesign factors.

( ) ( )Wt

L Wt Wt K Den V L

K Den

Den

Concrete

Driscopipe product Water Driscopipe Out

Water

Conc

=+ − × × ×

×

−

( )

1

Where:WtConcrete = Concrete dry land weight, lbsWtproduct = Density of internal fluid x internal volume of the pipeWtDriscopipe = Pipe weight, lbs/ftK = Anchor constant (1.0 to 1.5)L = Weight spacing, ft (10 to 15 ft is recommended)VDriscopipe (Out) = External volume of the pipe (water displaced), cu. ft/ ftDenWater = Density of the water, lbs/cu. ftDenConc = Density of the concrete, lbs/cu. ftDenproduct = Density of product being carried, lbs/cu. ft

ANCHOR SPACING The weight of the anchors develops a structural bending moment in thepipe during installation. The interval span must be limited to prevent excessive deflection of the pipebetween anchors (or strain in the pipe at the anchors). The spacing between anchors can becalculated for a given pipe DR using either deflection or strain as the limiting factor. In this calculation,the pipe is examined as an integrated series of simple beams between anchors. Figure 14 illustratesthe maximum span between concrete weights for all available diameters and DRs. Although theallowable spacing may be in excess of 10 to 15 feet, many users have sized their concrete anchorweights based upon this interval in order to minimize handling and installation problems.

51

FIGURE 14: MAXIMUM SPAN BETWEEN CONCRETE WEIGHTS FORUNDERWATER DRISCOPIPE® PIPELINES

EXAMPLE: Maximum Span Between Concrete Weights for Underwater Driscopipe PipelinesA 16" DR 15.5 Driscopipe line will carry a brine solution with a density of 72.9 pounds per cubic footacross a fresh water lake. Concrete weighing 150 lbs/ft3 will be used to fabricate the anchor weights.

GIVEN: DENWater = 62.4 lb/ft3

DENConc = 150 lb/ft3

VDriscopipe(Out) = (π/4) (16)2/144 = 1.396 cu. ft/ ft

WtDriscopipe = 21.21lbs/ft

Pipe ID = 16 - 2(1.032) = 13.936 in.

Wtproduct = (π/4) (13.936)2 (72.9)/144 = 77.22 lbs/ft

WtConcrete = ( . . ) ( . . . )

. ..

2121 77 22 13 62 4 139613 62 4

1501

32 3+ − × ×

×

−

= lbs/f

From Figure 14, the maximum weight spacing for 16” DR 15.5 is found to be 30 feet. Anchor spacing of tento fifteen feet is common. With weights 10 feet apart, each will weigh 10 x 32.3 = 323 lbs. If 400 poundweights are available, spacing will be 400/32.3 = 12.38 feet. The weights should be spaced at a 12 footinterval.

52

If air can get into the pipe, extra weight should be allowed, and the weights should be spaced moreclosely. Gas pipelines must be designed for underwater stability when full of gas at zero pressure andthus have a design ‘K’ greater than 1.0. In this situation, floats are required to install the pipeline.

If a current is present, movement of the pipe itself is not harmful. However, sharp rocks or otherobjects may damage the pipe. If waves or currents present a problem, the best solution is to trenchand bury the weighted pipeline.

FIGURE 15: ANCHOR WEIGHT DESIGNS

INSTALLATION OF MARINE PIPELINES Driscopipe polyethylene pipe is often floated intoposition on the water surface and then sunk slowly in a very gentle “S” configuration. For applicationswhere the pipe will not always be full of liquid or where the product will be lighter than water, veryheavy weights will be required. If additional flotation is required during installation, the floats should beattached at intervals before towing the pipeline onto the surface of the water.

Depending on site conditions, various procedures have been used to assemble the pipeline. Somecommon assembly procedures are as follows:

• Fuse the pipe together onshore into continuous lengths.• Assemble the ballast weights to the pipe onshore after fusion and before the pipe is

launched into the water.• Fuse the pipe together onshore and pull or push the pipe into the water as in the

previous procedure. Assemble the weights to the pipe from a barge.• The pipe can be fused on land with flanged connections added to each end. The

flanged ends are capped and the sections are launched onto the water to be laterassembled on the water. Such floating lines are often used in dredging operations.

Installation of the ballast weights is usually accomplished onshore. To minimize drag and aidmovement of the weighted pipe into the water, a wood or steel ramp can be fabricated at water'sedge. Ballast weights may be installed from a barge or raft.

53

Any pipe which is temporarily stored on a body of water should be protected from marine traffic andwave action. Waves could damage the pipe by pushing it against rocks or other sharp objects.

LAUNCHING AND SINKING Each end of the pipeline must be sealed to allow floatation until it isready to be installed. Typically, this is done with a flange assembly and metal blind flange. Thisprovides an airtight seal. The pipeline is then moved into position for sinking by marine craft.

The transition of the pipeline from the shore to the water should be done in a trench before the sinkingoperation begins. It is important to protect the pipeline from damage by debris, ice, boat traffic, andwave action.

The sinking operation is controlled by the addition of water to one end and the evacuation of theenclosed air through the opposite end. The addition of water to the pipeline at a controlled rate willensure that the pipe lies in the trench or adjusts to the profile of the bottom. The rate of sinkingshould also be controlled to prevent an excessive bending radius.

During the sinking process, water must be prevented from running the full length of the pipe. This canbe done by inducing a water pocket at the shore end by lifting the offshore pipe above the water.Water is introduced into the pipeline closest to shore allowing it to sink. Once the pipe reaches anequilibrium, additional water can be added gradually to completely sink the line.

After the pipeline is installed on the bottom or in the trench, a thorough inspection should be made ofthe pipe installation. All weights should be properly positioned and the pipe positioned in the center ofthe trench or within the right-of-way. The trenched area where the pipe leaves the shore and entersthe water should be adequate to protect the pipe from damage. Where backfill is used, inspect forproper installation and required depth.

It is better for a marine pipeline to be too long rather than too short. Never attempt to flange up apipeline that is too short by drawing the bolts together. This places the flanged connection in severetension and may cause leaks or a failure in the transition connection. Extra length can often beaccommodated by snaking the pipe.

INTAKE AND OUTFALL DIFFUSERS Phillips Driscopipe can provide special diffuser assemblies toterminate outfall pipelines. Special sinking provisions are sometimes required to expose the verticaldiffuser while subjecting it to as few navigational hazards as possible.

WATER SURFACE PIPELINES

Water surface pipelines are either floated on the surface or submerged just below the water surface.Polyethylene pipe is naturally buoyant. When filled with water, it floats just at the water’s surface.

MARSH PIPELINES

In marshy areas, the pipeline route should be surveyed to determine the soil conditions. Where theground is solid, it can be treated as a buried pipeline. Where there is a firm bottom, the installationcan be treated as an anchored marine pipeline. Where the area is boggy, the pipeline can beweighted to neutral buoyancy so that it neither floats nor sinks and then buried at a depth in line withthe rest of the pipeline.

Varying soil conditions may require the pipe’s DR to be matched to the performance characteristics ofpolyethylene pipe. For example, in silty areas where the soil is highly fluidized, the pipe design may

54

be examined by considering the mucky soil as a high specific gravity fluid exerting a heavier externalhydrostatic pressure than clear water.

SLIPLINED PIPELINES

Polyethylene pipe is commonly used for renewing old, deteriorated pipelines. The sliplining process isadvantageous because there is a minimum disruption of surface traffic and municipal service lines.Private property damage is reduced over direct burial applications and because of polyethylene’ssmooth surface, flow capacity is often maintained with a smaller sized pipe.

There are seven basic steps to the sliplining process. First, the existing line must be inspected.Video inspection equipment is used to examine the existing pipeline for leaks, obstructions, rootintrusion, or segments of collapsed or buckled pipe. Secondly, the line must be cleaned and cleared.A small segment of sliplined pipe may be pulled through the existing pipe to ensure the old line isadequately cleared for insert renewal. The polyethylene pipe is joined via the butt fusion process.The original line is accessed. PPI and ASTM have guidelines for the dimensions of the access pit.An appropriate pulling head is devised ,and the liner is pushed or pulled (or a combination of both)through the existing pipe. The pipe will experience tensile stress over the course of the insertion aswell as thermal stress from temperature changes. A 24 hour relaxation period is recommendedbefore making service and lateral connections to the polyethylene pipe. After the stabilization periodand the service connections are made, the final step in the sliplining process is to make terminalconnections and stabilize the annular space when it is necessary. See Figure 16 for more informationon transitioning polyethylene pipe into a concrete manhole.

Additional information on sliplining can be found in ASTM F585, “Standard Practice for Insertion ofFlexible Polyethylene Pipe into Existing Sewers” and the Plastics Pipe Institute document “PipelineRehabilitation with Polyethylene Pipe.”

FIGURE 16: SUGGESTIONS FOR TRANSITIONING POLYETHYLENE PIPE TOA CONCRETE MANHOLE

Through ManholeRemove top or drill holes to keepmanhole dry

Change of DirectionGood pullout resistance

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FIGURE 16, CONTINUED

BURIED PIPELINES

TRENCHING AND BED PREPARATION The trench width will vary with its depth and thetype of soil present. The bed width should allow for adequate compaction around the pipe. Theexcavated material, if it is rock free and well broken up by the ditcher, may provide a suitable beddingmaterial. Maximum particle size of Class I or Class II materials used for bedding, haunching, or initialbackfill should be kept to ½” for smaller pipe (< 8”) and a maximum size of 1” aggregate for pipediameters greater than 8”. Refer to PPI Technical Report TR-31, ASTM D2321, and ASTM D2774for more information on underground installation . The trench bottom should be relatively smooth and free of rock. Objects that may cause point loading on the pipe should be removed and the trench bottom

“Lined” ManholeGood pullout resistance

Grouted in WallFair pullout resistance

Gas/Water TightGood pullout resistance

Spool ConnectionGood pullout resistance

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padded using 4-6 inches of tamped bedding. If an unstable soil condition exists, the trench bottomshould be undercut and filled to proper trench depth with a selected material.

Unless specified, accurate leveling of the trench bottom is unnecessary for most pressurized systems.The slope should be graded evenly in gravity flow systems.

When joined by the heat fusion method, polyethylene pipe is a joint free piping system. Typically,polyethylene pipelines do not require thrust blocks. Good soil compaction around fittings such aselbows or tees is usually sufficient. If thrust blocks are used, sufficiently sized concrete encasementor concrete bearing surfaces set in undisturbed soil will provide adequate protection. Theencasement or thrust block should be constructed of reinforced concrete and act as an anchorbetween the pipe or fitting and the solid trench wall. Figure 17 illustrates various types of concreteblocking and encasement of fittings.

FIGURE 17: EXAMPLES OF CONCRETE THRUST BLOCKS AND ENCASEMENTS

The following information on direct burial references ASTM D 2321, “Recommended Practice forUnderground Installation of Flexible Thermoplastic Sewer Pipe”. Refer to Figure 18 for termsassociated with burial of polyethylene in a trench.

• The trench bottom should be smooth, dry, and stabilized as necessary.• If a bedding material is required, it should be of a suitable material as identified by ASTM D

2321. The material should be leveled and compacted to a minimum of 85% Standard ProctorDensity.

• Place backfill material under the pipe haunches.• Tamping is required around the haunches using suitable tools.• Primary and secondary backfill should be placed evenly in layers not exceeding 12 inches,

and each layer should be compacted to a minimum of 85% Standard Proctor Density.

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• The primary backfill should normally extend to a height equal to 75% of the pipe diameter. Ifthe pipe is to be placed below the water table, consult the project engineer to determine theheight of this zone.

• The secondary backfill should normally be 12 to 18 inches above the crown of the pipe.Consult the project engineer to determine if additional material is required.

• The final trench backfill, or trench spoil, should be of material which is free of large stones orother foreign matter.

• Adequate compaction should be obtained before any equipment is driven over the pipe.

Consult the project engineer before burial of any pipe to determine backfill specifications and specialconditions.

FIGURE 18: TRENCH CONSTRUCTION AND TERMINOLOGY

Foundation (maynot be required)

12”-18”

Bedding

Invert

CrownPrimaryBackfill

Excavated Trench Width

PipeZone

SecondaryBackfill

FinalBackfill

Springline

Haunch Zone

PIPE LAYING Polyethylene pipe can be joined at ground level and lowered into the ditch. Excessstress or strain should be avoided during installation. Flanged connections should be used asnecessary to facilitate the handling of pipe and fittings into and out of the fusion machine and duringinstallation.The length of pipe which can be pulled into position depends on the pipe size and wall thickness. Thepulling force that can be applied to a pipe on level ground can be estimated with the following formula:

F = SA

Where: F = Maximum pulling force, lbsS = Maximum allowable stress (conservatively 1000-1600 psi)A = Cross-sectional area of pipe wall, in.2

When pulling pipe, use care to prevent the pulling cables from damaging the pipe. Never pull the pipeby the flanged end! Refer also to ASTM F1804, Standard Practice for Determining ATL on PE Gas Pipe.

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FITTING INSTALLATION When fittings are connected to rigid structures, movement orbending should be prevented. The backfill must be compacted to provide full support, or a concretesupport pad should be constructed beneath the pipe and fitting. Particular attention should be given tothe compaction achieved around the fittings and extending several pipe diameters beyond the ends ofthe fitting. Compaction of 90% Proctor Density or greater in these areas is recommended. If aconcrete pad is used to provide support, it should be rigid and extend one pipe diameter or a minimumof 12" from the flanged joint. See Figure 19 for suggested methods.

The bolts in the flanged connection as well as the clamps in a support pad should be retightenedbefore burial. Surface connections can be observed while in operation.

Polyethylene pipe or fittings can be encased in concrete if required by the design. Reinforcedconcrete encasement can be used to raise pressure rating of fittings, to stabilize heavy valves orfittings, and to control thermal expansion or contraction.

FIGURE 19: CONCRETE SUPPORTS FOR A FLANGED CONNECTION

CAUTION: Driscopipe fabricated fittings are manufactured by fusing together pipe segments toobtain the desired fitting. In most cases, the pressure rating of a fabricated fitting is 75% of the ratingof a molded fitting with the same thickness. Precautions must be taken when installing them into apiping system. Refer to Technical Note #43 from Phillips Driscopipe.

Fabricated fittings, after being fused to the pipe, can be damaged by excessive strain created byimproper handling. Driscopipe resins are very tough; however, the tensile strength of polyethylene ismuch less than steel ,and it will not support the excessive lifting and pulling forces that can be exertedby powered installation equipment. If pipe is fused to the three sides of a tee and lifted withoutsupporting the weight of the pipe, the tee may be torn apart. Fabricated fittings must not be allowed tocarry the weight of the pipe!

Installation procedures should minimize lifting and moving of assembled pipe and fabricated fittings. Ifit is necessary to pull the assembly into position, the fabricated fitting, flange adapter or stub endshould never be used as the point of attachment for the pulling line.

It is difficult to fusion join a fabricated tee or wye into a system because the assembly is complicatedby the third side. Handling becomes a problem when pipe is joined to the third side. Final handlingand positioning of these assemblies requires additional precautions.

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MANUFACTURER’S RECOMMENDED ALTERNATE METHOD The potential for damage to afabricated tee or wye can be minimized by including a flanged connection on the branch side of thefabricated fitting. This allows final positioning to takeplace before the branch side is connected. It isstrongly recommended that flanged connections beused on the branch side of fabricated tees and wyesand on one end of elbows, especially in sizes above24”.

PRESSURE TESTING DRISCOPIPE SYSTEMS

Driscopipe piping systems should be pressure tested before being put into service. Water is thepreferred test medium. After all free air is removed from the test section, raise the pressure at asteady rate to the required pressure. The pressure in the section shall be measured as close aspossible to the lowest point of the test section.

The pressure test can be conducted before or after the line is backfilled. The pipe should be coveredat intervals, particularly at curves to hold it in place during pressure tests. Flanged connections maybe left exposed for visual leak inspection.

Test pressure should not exceed 1.5 times the rated operating pressure of the pipe or the lowest ratedcomponent in the system. Initially, the pipe should be raised to test pressure and allowed to standwithout makeup pressure for a sufficient time to allow for expansion of the pipe. This usually occurswithin 2-3 hours. After equilibrium is established, the test section is pressurized to 1.5 timesoperating pressure, the pump is turned off, and the final test pressure is held for 1, 2, or 3 hours.

Polyethylene pipe holds pressure by developing stress in its walls. This process continues throughoutthe test period and the pipe increases slightly in diameter. Pressure drop will occur due to continuedexpansion of the pipe during the second phase of the test. A drop in pressure during the test phase iscommon and does not prove with absolute certainty that a leak or failure is present in the system.Polyethylene pipe is tested by measuring the “make up” water required to return the section to testpressure. Allowable amounts of makeup water for expansion during the pressure test are shown inTable 16 from PPI Technical Report TR 31. If the test pressure is not returned within the allowablevolume of water, the test fails. If there are no visual leaks or significant pressure drops during the finaltest period, the pipeline passes the test.

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TABLE 16: ALLOWANCE FOR EXPANSION UNDER TEST PRESSURE*

Allowance for Expansion(U.S. Gallons / 100 Feet of Pipe)

Nominal PipeSize (Inches)

1 HourTest

2 HourTest

3 HourTest

3 0.10 0.15 0.254 0.13 0.25 0.406 0.30 0.60 0.908 0.50 1.0 1.510 0.75 1.30 2.1011 1.0 2.0 3.012 1.1 2.3 3.414 1.4 2.8 3.216 1.7 3.3 5.018 2.2 4.3 6.520 2.8 5.5 8.022 3.5 7.0 10.524 4.5 8.8 13.328 5.5 11.1 16.832 7.0 14.3 21.536 9.0 18.0 27.040 11.0 22.0 33.048 15.0 27.0 43.0

*These allowances only apply to the test period and not to the initial expansion phase.

Testing of non-pressure, gravity flow pipes, whether above or below ground, may be accomplished byclosing all openings below the top of the section to be tested. For test purposes, provide a means toraise the water level to a height of at least 3-5 feet above the highest point in the line being tested. Thewater level should be maintained for a time long enough to determine if leaks are present. If it isimpractical to raise the water level as suggested, the line can be pressurized with low pressure water.Normally, pressure should not exceed 5-10 psi over a time period of 5-10 minutes.

CAUTION: Changes in temperature will increase or decrease the apparent test pressure in anypiping system. The effect depends on the rate of expansion of the pipe wall compared to the water inthe pipe. Polyethylene has a higher rate of expansion and contraction than water. When a Driscopipesystem becomes heated (e.g. on a sunny day), the system pressure will decrease. When a sealedDriscopipe system becomes cooler, the system pressure will increase. When possible, testing shouldbe done during periods of relatively stable atmospheric temperatures. Early mornings and lateafternoons are good times to test the pipe when it has not been buried.

Under no circumstances shall the total time under the test exceed eight (8) hours at 1.5 times thepressure rating of the lowest rated component in the system. If the test is not completed due toleakage, equipment failure, etc., the test section shall be allowed to “relax” for eight (8) hours prior tothe next test.

REPAIR TECHNIQUES

PERMANENT REPAIR Repair can be accomplished on small diameter pipe by openingsufficient trench space and cutting out the defect. Replace the damaged section with a new segmentof pipe.

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Repairing large diameter pipe can be accomplished with a flanged spool piece. The damaged sectionis removed. Next, the butt fusion machine is lowered into the ditch. Flanged connections are fused toeach open end, and the flanged spool assembly is bolted into place. The flanged spool must beprecisely made to fit the resulting gap in the pipeline. Figure 18 illustrates these methods.

FIGURE 20: USING FLANGED CONNECTIONS TO REPAIR A DAMAGED PIPE SECTION:

MECHANICAL REPAIR Wrap-around repair clamps with an integral gasket can be used butare not as permanent as a flanged or fused repair. This type of repair is principally used in buriedapplications because the compacted soil restrains the pipe from thermal movement and pull-outforces caused by internal pressure. A longer repair clamp generally provides greater sealingcapability on thermoplastic pipe. A minimum clamp length of 1.25 - 2 times the nominal pipediameter is recommended. After the pipe is wiped clean of all foreign material, the clamp should betightened evenly. After the clamp is installed, backfill and compact around and over the pipe before itis pressurized.

FITTING REPAIR Failed fittings are usually replaced by flanging a new fitting into the system.Repairs using hot air or extrusion welding are not recommended.

UNDERWATER REPAIR To accomplish underwater repair on a pipeline, the pipe ends mustbe raised above the water and a flange assembly fused to each end. The ends are then lowered intoposition on the bottom and bolted together underwater. In some cases, a spool piece must befabricated to retie the pipeline.

Appropriate lifting equipment must be used to ensure that the pipe does not kink and that theminimum bending radius is not exceeded. Normally, it is unnecessary to remove the weights beforelifting. However, extreme care should be exercised when lifting the pipe above the water level withweights attached.

MISCELLANEOUS REPAIR METHODS Under certain situations, a thermofit heat shrinksleeve or an electrofusion repair patch can be used to seal a puncture or leaking joint. Many types ofsleeves are available. The sleeves are coated on the inside with a special sealant. When heated, thesealant forces into a puncture or joint and prevents further leakage.

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SHIPPING, HANDLING, AND UNLOADING

SHIPPINGThe normal method of shipment is by truck. Standard packaging for Driscopipe industrial pipe isshown below.

TABLE 17: STANDARD PACKAGING FOR DRISCOPIPE ® INDUSTRIAL PIPE

40 Foot 40 Foot Loose Pipe Diameter Bundle Truck Load (Bundled) Truckload Load *

Nominal O.D. Number of Linear Number of Linear Number of LinearSize Inches Joints Feet Bundles Feet Joints Feet

1” 1.315 116 2,320 48 (20 ft bundles) 111,360 --- ---1-1/4” 1.660 153 3,060 28 (20 ft bundles) 85,680 --- ---1-1/2” 1.900 129 2,580 28 (20 ft bundles) 72,240 --- ---

2" 2.375 88 3,520 14 (40 ft bundles) 49,280 --- ---3" 3.500 50 2,000 14 (40 ft bundles) 28,000 --- ---4” 4.500 29 1,160 14 (40 ft bundles) 16,240 --- ---5" 5.563 15 600 14 (40 ft bundles) 8,400 --- ---6" 6.625 13 520 14 (40 ft bundles) 7,280 --- ---7" 7.125 11 440 12 (40 ft bundles) 5,280 --- ---8" 8.625 9 360 10 (40 ft bundles) 3,600 --- ---

10" 10.750 --- --- --- --- 85 3,40012" 12.750 --- --- --- --- 56 2,24014" 14.000 --- --- --- --- 48 1,92016" 16.000 --- --- --- --- 39 1,56018" 18.000 --- --- --- --- 27 1,08020" 20.000 --- --- --- --- 20 80022" 22.000 --- --- --- --- 18 72024" 24.000 --- --- --- --- 14 56028" 27.953 --- --- --- --- 10 40032" 31.496 --- --- --- --- 8 32036" 36.000 --- --- --- --- 6 24042" 42.000 --- --- --- --- --- ---48" 47.496 --- --- --- --- --- ---54" 54.000 --- --- --- --- 2 80

*102” wide trailer with 96.25” of loading space with pipe stakes

Polyethylene, like most plastics, is softer than steel. Hauling, unloading, and installing Driscopipeproducts should be done with the care necessary to prevent damage to the pipe. Poor handling canresult in abrasions, cuts, gouges, and punctures.

Coiled pipe is available in ½” through 6” sizes. 500’, 1000’, and 1500’ lengths are most common,though several larger and smaller coil lengths are available. Please contact your local distributor orPhillips Driscopipe for more information.

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HANDLINGAll pipe should be carefully examined before installation and damaged pipe removed. Cuts andgouges that reduce the wall thickness by more than 10% may impair long-term service life. PhillipsDriscopipe recommends these areas should be cut out and discarded. Minor scuffing or scratchingwill have no adverse effect on the serviceability of Driscopipe products.

Damaged pipe may be repaired by any of the joining methods previously discussed. Heat fusion ispreferable for all applications where conditions permit. Some joining methods (e.g. extrusion welding)are not satisfactory for continuous pressure systems.

Joints should be handled near the middle with wide web slings and spreader bars. Coils can behandled in a similar manner. The use of chains, end hooks, or cable slings is not recommended. Thefollowing procedures should be used when handling Driscopipe products:

• When shipping or storing polyethylene pipe, always stack the heaviest pipe at thebottom.

• Protect the pipe from sharp edges when overhanging the bed of a truck or trailerby placing a smooth, rounded protecting strip on the edge of the bed.

• Polyethylene pipe has a very smooth inner and outer surface. Anchor the loadsecurely to prevent slippage.

• Lengths of small-diameter, lightweight pipe can be unloaded manually.

The following procedures are commonly implemented when handling Driscopipe productsprior to and during the heat fusion process.

• Pipe is stacked beside the fusion unit, fused, and pulled into position forinstallation. Care must be taken to prevent damage from rocks orexcessive abrasion during the pulling process.

• To prevent excessive loading on the fusion machine’s hydraulic system,additional joints of unfused pipe are placed in the moveable jaw of thefusion machine. The fixed jaw holds the previously fused long length ofpolyethylene.

• “Stringing” the pipe and moving the fusion machine is inefficient and isnot typically used during construction.

BENDING The minimum bend radius varies with the DR of the pipe. Thin wall pipe can be fieldbent to a minimum radius of 40 times the pipe diameter. Thick wall pipe can be bent to 25 pipediameters. Refer to Table 2.

KINKS Normally, kinks do not impair the serviceability in low pressure applications. For highpressure applications, severe kinks should be cut out and the pipe re-joined by fusing.

OVALITY Out-of-roundness due to excess loading during shipment or storage will not hinder theserviceability of the pipe. The pipe should not be considered damaged unless the fusion machineclamps cannot successfully round out the section for a good fusion joint. Occasionally, the pipe canbe placed in an unstressed condition so that it will relax and gradually round out.

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UNLOADINGThe following recommendations are given for unloading Driscopipe pipe:

• Be sure the unloading equipment is rated to handle the weight of thepipe.

• The unloader must have adequate room on both sides of the trailer.Advise all persons except lift operator to stand clear of the trailer.

• Unload one pallet, bundle, or strip load layer at a time. Truck strapssecuring a bundle or strip load layer should be released when that bundleor layer is to be unloaded.

• Never stand on a load of pipe.

STORAGE If the pipe must be stacked for storage, avoid excessive stacking heights and stack the pipe instraight rows. The pipe can be deformed if it is not stored properly. General stacking heightsdeveloped by the Plastic Pipe Institute for polyethylene pipe are shown in Table 18.

Since Driscopipe HDPE pipe contains greater than 2% carbon black, it will resist damage fromsunlight. Expansion and contraction caused by uneven heating in the sun may cause the pipe to bowif not restrained by racks. This does not damage the pipe but may be inconvenient when the pipe istaken out of storage for installation.

When the pipe is laid directly on the ground, rocks and other objects that may scar or gouge the pipeshould be avoided.

TABLE 18: ALLLOWABLE STACKING HEIGHTS FOR DRISCOPIPE ® HDPE PIPE

Number of Rows High

Nominal Pipe SDR* 18 SDR > 18 SDR > 26 Size, inches and smaller to SDR 26 to SDR 32.5

4 45 26 146 31 17 108 24 13 8

10 17 10 612 13 8 514 12 7 416 11 6 418 10 6 420 9 6 322 8 5 324 7 4 328 6 4 332 ------ 3 236 ------ 3 240 ------ ------ 248 ------ ------ 2

*Note: SDR = Standard Dimension Ratio = OutsideDiameter

MinimumWallThickness

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INDEX

Abrasion resistance 2Advantages 2Air Pressure 6Anchoring 36, 54-56, 58

Applications 2ASTM D1248 8ASTM D3350 1, 8Below ground installation 55-57

Bend radius, minimum 5Benefits 2Buckling 42Buoyancy 50-53

Buried pipelines 10-12, 32, 35-46Butt fusion 6, 9Cautions 6-7, 12Cell classification 8

Characteristics of HDPE 2-6Chemical resistance data 2-4, 10Chlorine 13Coils 7, 12

Collapse 43, 50Contaminated soil 13Contingency and risk 13Cooper E-80 42

Crushing 42Deflection 26, 30-31,44-46Density 10Design Data 10-11, 14Dimension ratio 14

Disinfecting 13Expansion coefficient 6, 29Fabricated fittings 2, 58-59Fatigue resistance 16-17

Figures, List of IVFittings 2, 9, 20, 58-59Flexibility 5

Floats 50Flow characteristics 17-18, 23-24Flow factors 5, 17, 22Fusion 6, 9

Gas flow 28Gluing 10Gravity flow 21-25Grouting 28

H20 Live Load 41Handling 63Hazen/Williams flow factors 5, 19Hazen/Williams formula 18-19

Hydrostatic design basis 14-15, 29Hydrostatic design stress 14-15Insect attack 13Insert renewal 27-28, 54

Installation considerations 12-13Joining methods 9Kinks 63Life expectancy 5

Lightweight 5Loads 12, 35-46Locating 7Longitudinal Stress 17

Manhole connections 54-55Manning equation 21Manning s number 5Marine pipelines 12, 32, 50-53

Marsh pipelines 12, 53-54Materials 8Mechanical joining 9, 61Minimum cover 36

Modulus of Elasticity 29, 43Movement 6, 11, 30Ovality 63Overland pipelines 11, 31, 49

Permeability 10, 13Phillips Petroleum Company 1Pressure drop through fittings 19-20Pressure ratings 5,10, 14-16, 26, 29

Pressure surge 11, 16-17Pressure testing 59-60Pulling force 57Repair techniques 60-61

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Scope 1Shipping 62Sliplining 27-28, 54Slurries 22-25

Smoothness factor 5, 18Soil modulus, E 36Soil pressure 36-42Stacking heights 64

Static Electricity 7, 12-13Storage 64Stress 15, 17, 30Supported pipelines 11, 47-49

Surge 11, 16-17Tables, list of IIITemperature range 6, 11Temperature rerating 26

Testing polyethylene pipelines 7, 59-61Thermal conductivity 30Thermal expansion/contraction 6, 29-32Threading 10Thrust blocks 56

Toughness 6Transition connections 32Trenching 55-57Ultraviolet Protection 6

Underwater installation 50-54, 61Unloading 7, 64Vacuum or suction pipelines 11, 25-26, 42Velocity 17, 23

Viscous fluid pressure drop 20Water hammer 11, 16-17Weatherability 6Working pressure rating 29

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