HDI Manual

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-i

A Training Program Presented

by

Horizontal Drilling International

Houston, Texas, USA & Paris, France

for

Sumitomo Metal Industries, Ltd.

Osaka & Tokyo, Japan

February 1999

HorizontalDirectional

Drilling

TrainingManual

HorizontalDirectional

Drilling

TrainingManual


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1999 Horizontal Drilling InternationalHouston, Texas, USA, & Paris, France

All rights reserved.

This publication, including all paper and electronic copies, is strictly confidential and the soleproperty of Horizontal Drilling International. No part of this publication may be reproduced, stored in a

retrieval system, or transmitted in any form or by any means electronic, mechanical, recording, orotherwise, without the prior written permission of Horizontal Drilling International.

Illustrations produced by ALBACORE, Paris, France.Technical editing, desktop publishing, and electronic publishing by

The Write Enterprise, Houston, Texas, USA.


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-iii

Contents

Chapter 1

Planning and Scheduling

Chapter 2

Engineering

Chapter 3

Steering

Chapter 4

Reaming

Chapter 5Pullback

Chapter 6

Mud

Appendix A

Units and Abbreviations

Appendix B

Glossary


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Chapter 1: Planning and Scheduling

Introduction ........................................................................................ 1-1

Horizontal directional drilling .............................................................................. 1-1The importance of planning and scheduling ...................................................... 1-1Case study ......................................................................................................... 1-1

Dimensions and characteristics of the crossing...............................................................1-1

Soil investigation report ...................................................................................................1-2

Identifying tasks ................................................................................................. 1-2

Site Visit .............................................................................................. 1-3

Access................................................................................................................ 1-4Rig side .............................................................................................................. 1-4Water source...................................................................................................... 1-4Pipe side ............................................................................................................ 1-4

Tru Tracker coils............................................................................................. 1-5Obstacles and local constraints ......................................................................... 1-5Communications ................................................................................................ 1-5Accommodations and board .............................................................................. 1-6

Planning and Estimating Costs ........................................................ 1-6

Size of the drilling rig and support equipment.................................................... 1-6Drilling method and tools.................................................................................... 1-7

Pilot hole ..........................................................................................................................1-7

Reaming............................................................................................................................1-8

Pulling ..............................................................................................................................1-8

Anchorage of rig...............................................................................................................1-8

Subcontracts ...................................................................................................... 1-8Work schedule ................................................................................................... 1-9Quantities........................................................................................................... 1-9

Crew .................................................................................................................................1-9

Drilling accessories........................................................................................................1-10

Drilling consumables......................................................................................................1-10

Rig consumables and spares ..........................................................................................1-11

Mobilization/demobilization...........................................................................................1-11

Other considerations........................................................................................ 1-12

Customs duties and taxes................................................................................................1-12

Local taxes......................................................................................................................1-12

Insurance ........................................................................................................................1-12

Weather conditions.........................................................................................................1-12

Terms of payment ...........................................................................................................1-12

Bid bond..........................................................................................................................1-12

Performance guarantee..................................................................................................1-12

Bank guarantee upon completion...................................................................................1-12

Closing meeting ............................................................................................... 1-12


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ii

Preparing to Work.............................................................................1-13

Permits .............................................................................................................1-13Equipment ........................................................................................................1-13

Rig and spare parts ........................................................................................................ 1-13

Drill pipes and downhole tools ...................................................................................... 1-13

Pumps and spare parts................................................................................................... 1-13

Recycling equipment and spare parts ............................................................................ 1-13Pipe rollers and cradles................................................................................................. 1-13

Transporting equipment................................................................................................. 1-13

Clearing customs............................................................................................................ 1-13

Personnel .........................................................................................................1-13

Selecting the crew .......................................................................................................... 1-13

Briefing the superintendent and assistant...................................................................... 1-14

Transporting the crew.................................................................................................... 1-14

Consumables....................................................................................................1-14

Bentonite ........................................................................................................................ 1-14

Water.............................................................................................................................. 1-14Fuel ................................................................................................................................ 1-14

Electric wire................................................................................................................... 1-14

Line of sight and coil installation.......................................................................1-14Subcontracts.....................................................................................................1-14

Civil works ..................................................................................................................... 1-14

Sheet piling for rig anchorage ....................................................................................... 1-15

Mud return line .............................................................................................................. 1-15

Mud trucking.................................................................................................................. 1-15

Pipeline prefabrication .................................................................................................. 1-15

Buoyancy control system................................................................................................ 1-15

Mud removal .................................................................................................................. 1-15

Communications and coordination ...................................................................1-16

HD-650 drill unit.


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iii

List of Figures

Fig. 1.1. Soil investigation report. ....................................................................................1-2

Fig. 1.2. Map view of job site...........................................................................................1-3

Fig. 1.3. Size of the drilling rig. .......................................................................................1-6

Fig. 1.4. Typical maxi-rig.................................................................................................1-7

Fig. 1.5. Typical marine installation...............................................................................1-16

List of Tables

Table 1.1. Bentonite consumption estimates. .................................................................1-10

Pipeline pullback.
http://planning%20%26%20scheduling/P&S%20layout.pdfhttp://planning%20%26%20scheduling/P&S%20layout.pdf


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Notes


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Chapter 1: Planning and Scheduling

Introduction

Horizontal directional drilling

Horizontal directional drilling (HDD) is atechnique that comes from the oil field, but

it is applied to the crossing of rivers, rail-

ways, motorways, dikes, and other

obstacles. The drilling assembly has a bent

sub for steering purposes, and is equipped

with an electronic probe to continuously

report the position of the pilot hole to the

driller. Interpreting this information allows

the pilot hole to follow the designed path.

The hole is lubricated and the cuttingsremoved by using drilling mud (generally

bentonite-based mud). This process is

repeated until the drill bit exits on the other

side of the obstacle.

Then the pilot string is removed and thehole enlarged by reaming according to thediameter of the pipeline or conduit to beinstalled. This is done with a reamer orhole opener, which is pulled and rotatedinto the pilot bore. The bentonite carriesthe cuttings out of the hole, and leaves alining (the filter cake

) on the wall of thebored pathway. Arriving at the final sizerequired for the reamed hole may requireone or more passes.

The pipeline or conduit, which has beenassembled in one continuous string, if pos-sible, is placed on launching rollers or in aflotation ditch. It is then connected to thedrill pipe by a swivel joint, preceded by areamer and is pulled into the reamed hole.

The importance of planning and scheduling

This course is designed to assist the Sumit-omo project manager in planning andscheduling an HDD project. This chapterreviews all questions that should be

answered when a project is in planning, out

for bid, or in the process of mobilization.By taking the time to answer these ques-tions in the early stages of the project, theproject manager will save his company

time and money.

Case study

A case study designed to walk you throughthe various planning stages is presentedthroughout this chapter. Project specificsfor the case study are set in green italicizedtype, as follows:

This case study concerns a seaway cross-ing, the Ij Meer, near Amsterdam in the

Netherlands. It was awarded to HDI inearly May 1995 and construction tookplace in June 1995.

Dimensions and characteristics of thecrossing. Typically, by the time the projectis assigned to the project manager, thepipeline route has already been established.This being the case, the HDD consider-ations concerning route selection will notbe considered here. However, in those

instances where the project manager haspreliminary input to the pipeline route, fol-lowing these guidelines whenever possiblewill minimize construction risk:

Keep the crossing as short as possible.Crossings less than 1000 ft (300 m) areconsidered short, crossings between

1000 and 2950 ft (300 and 900 m) areconsidered medium, crossings between2950 and 4600 ft (900 m and 1400 m)are considered long, and crossingslonger than 4600 ft (1400 m) are con-sidered extremely long.

Keep the entry and site exit sides of thecrossing as close to the same elevationas possibletry to avoid elevation dif-ferences of more than 50 ft (15 m).


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Horizontal Directional Drilling Training Program

1-2

Avoid routes where the pipeline cannotbe constructed in one continuousstring.

Maintain a minimum separation of50 ft (15 m) from other existing pipe-lines.

Cross the river or obstacle in a straight

line.

Avoid placing a crossing near large

masses of steel, such as railroad

bridges, steel piling, or docks where

barges are moored.

The client provided the following data forthe project:

Pipeline diameter: 16 in. (406.40 mm)

Wall thickness: 0.75 in. (19.10 mm)

Coating: 0.12 in. (3 mm) polyethylene (PE)Length of the crossing: 3821 ft (1165 m)

Width of the watercourse: 3018 ft (920 m)

Depth of the crossing: 100 ft (30 m)

Vertical drilling radius: 1640 ft (500 m)

Banks: No significant difference in eleva-tion

Construction period: Award in three weeksand construction within three months

Other: Horizontal curve 8 at

2/3 of thecrossing with 1640-ft (500-m) radius.

Soil investigation report. The single mostimportant consideration to the directionaldrilling contractor is the nature of the soilsat the crossing location. The subsurfacecondition is the primary factor in determin-ing the methods, price, and feasibility of aproject. Clients should provide geologicalinformation with their tender document.

In this project, the subsoil consists of alter-nating layers of clay, silty clay, peat, and

sand (Fig. 1.1). The navigation channeloverlies a deep sand deposit. StandardPenetration Test results range from 10blows per foot (bpf) in the peat layer to25 bpf in the clay layers, and average35 bpf in the sand formations. No sieveanalysis was provided.

Fig. 1.1. Soil investigation report.

Identifying tasks

The first task is to assess the feasibility ofthe crossing by HDD. The project managerwill review and analyze the data provided

by the client and visit the site, preferablywith a client representative.

1 Soil boring

1


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Planning and Scheduling: Site Visit

1-3

The second task, once the feasibility of theproject is confirmed, is to estimate the con-struction costs. For this purpose, the projectmanager will determine the necessaryequipment and crew, assess the drilling,reaming and pulling methods (types oftools and sequences), prepare a tentativeconstruction schedule, and estimate quanti-

ties of consumables. Then the selling pricecan be determined.

When the offer is accepted by the client,the project manager must mobilize all thenecessary equipment and consumables,finalize the necessary subcontracts, andbrief the construction crew about the spe-cifics of the project.

The following pages will take you through

the complete exercise, based on the specif-ics of the case study.

Site Visit

It is useful to visit the site with a client rep-resentative, because they will oftencommunicate their concerns about localrestrictions and regulations placed on themby governing bodies. During this site visit,take relevant photographs and write a

report to document what has been seen anddiscussed; it is common that the actual con-struction takes place several months afterthe initial site visit. If the contract specifi-cally states, Grounds (or roads) will bereturned to their original condition, thephotographs are especially useful to docu-

ment that you have complied with contractspecifications.

For this project the client organized anonsite meeting with all the prequalifiedcontractors, followed by a site visit. During

the meeting they were very specific aboutthe accuracy of the drilling profile: the per-mit allowed for a corridor of only 20 ft(6 m) wide, which would be checked by agyroscopic survey performed after theprojects completion by a third party at theclients expense (Fig. 1.2).

Fig. 1.2. Map view of job site.

1 Pipeline route

2 Initial crossing alignment

3 Revised crossing alignment

1

1

3

2


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1-4

Access

Because the drilling spread consists ofwheel-mounted loads that average 25 tonseach and measure approximately 40 ft longand 13 ft high (12 m long and 4 m high),make sure that it is possible to deliver allthe equipment to the rig side of the cross-ing. For this reason, make note of lowbridges, sharp turns in roadways, or any-thing else that may impede access. Usuallythe access to the crossing site is a tempo-rary construction road (dragline skids,

gravel) and the length of this temporaryaccess road must be estimated during thesite visit. The same is true for access to thepipe side.

Access to the Ij Meer rig site is straightfor-ward, via highway and paved road until260 ft (80 m) from the entry point. The pipe

side is accessible by barges or, for light

equipment, by a narrow paved road.

Rig side

A crossing with the maxi-rig requires adrilling site of 200 x 200 ft (60 x 60 m),while a crossing with the midi-rig onlyrequires a site of 70 x 100 ft (20 x 30 m).

For a large crossing through rock or coarsegranular materials, the workspace shouldbe increased to 200 x 260 ft (60 by 80 m).

The total available workspace is sufficient,but the entry point chosen by the client istoo close to the embankment of the adja-cent road. During the site visit with the cli-

ent, it was agreed that the entry point beshifted by 10 ft (3 m), which is far enoughfrom the embankment (Fig. 1.2, item 3).Any shift in the entry point must stay withinthe crossing corridor approved by the riverauthorities.

Water source

During the site visit, determine the fresh-

water source for mixing the mud:

City water: Can city water from a

hydrant be used? What notice is

required by the city water companies?

Is a meter required? Where is that

arranged? What is the cost?

River water: Can water from the river

be used? Is it fresh water?

If the available water source is locatedsome distance from the planned entrypoint, the drilling spread must have enough

hose and pump capacity to move therequired volumes the distance and eleva-tion changes that you will encounter.

There is no problem with pumping largequantities of river water in the Ij Meer, butthe water salinity must be checked. A labo-ratory test confirms a salt content of lessthan 120 mg/l, which is acceptable for mix-ing the bentonite (see Mud,page 6-14).

Pipe side

Ideally, the pipe side should have enoughtemporary workspace to lay the pipeline ina continuous string in the axis of the cross-ing. The pipeline should be prefabricated inthis temporary workspace starting approxi-mately 50 to 100 ft (15 to 30 m) beyond theexit point. This space should be 30 to 50 ft(10 to 15 m) wide, depending on the diam-eter of the pipe. Larger-diameter pipelinesrequire larger pieces of equipment and

therefore more working room. At the exit

location, a temporary workspace of 50 ft

wide by 100 ft long (15 by 30 m) is ideal

for most intermediate crossings. For large

crossings through rock or coarse granular

materials, a temporary workspace 100 ft

wide by 150 ft long (30 by 45 m) may be

needed to accommodate the necessary

equipment.


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Planning and Scheduling: Site Visit

1-5

In some cases (especially swampy areas),the roller track can be replaced by a flota-tion ditch.

In this area, the pipeline cannot be built in

line with the drilling alignment. However,by curving the right-of-way 45

about

160 ft (50 m) after the exit point, the3821-ft (1165-m) pipeline can be welded inone section along a road that must stay

open for traffic. A temporary bridge, made

of rollers placed on top of containers, isinstalled to cross the road.

At the exit point, no room is available forplacing a mud pit. Because of the access,no vacuum trucks can reach the site. There-fore, a small desanding unit is needed topreclean the mud; then the mud is pumped

across the Ij Meer back to the rig sidethrough a temporary 6-in. (150-mm) high-density polyethylene (HDPE) pipe attachedto a 2-in. (50-mm) steel cable to sink it.

Tru Tracker coils

On both sides of the river, permission is

needed to set up a wire Tru Tracker coil

from the edge of the water to either the

entry or exit points. Generally, these coils

are set as wide as the crossing is deep at the

particular location. Setting these coils dis-

turbs very little of the surface vegetation.

For a complete discussion of setting TruTracker coil, see Steering (page 3-30).

A coil could not be installed on the pipe

side because of housing and private prop-erties. On the rig side, the coil could beinstalled, but very little room was leftbetween the entry point and the riverbank.

Obstacles and local constraints

During the site visit, identify obstaclessuch as existing pipelines, cables, or sheetpilings. Massive steel structures such aspilings, pipelines, or high voltage lines willdisturb the local magnetic field and createinterference for the steering tools. In thesecases, it is almost mandatory that the TruTracker locating system is used to drillaccurately.

Constraints such as neighboring housing,which limits the acceptable noise level, orspecial environmental considerations aboutthe handling of mud, should also be identi-fied at this stage.

At the Ij Meer location, there was no such

constraint. However, because of the narrow

corridor allowed by the water authorities,

wooden piles were installed to aid the lay-

ing of Tru Tracker coil at intervals alongthe crossing. Also, a very strict criterion

was determined for accepting the pilot hole

data: if a reading made in the coil is more

than 7 ft (2.2 m) away from the centerline,

it is rejected and the joint is redrilled (the

corridor allows for 10 ft [3 m], so the read-

ing must be accurate2% of the depth

and a half-diameter of pipe).

Communications

During the site visit, locate the shortestroutes to transport equipment and person-nel from one side of the crossing to theother. On a large crossing that lacks abridge, a barge and tug must be planned.

The Ij Meer is very shallow outside thenavigation channel and barges cannot beused. Therefore, only the narrow road canbe used, which means limiting the numberof trucks and allowing no vacuum truck tobe used; hence the mud return line. Crewmembers can easily get from one side to theother by car. A boat is needed to install andoperate the Tru Tracker coil.


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1-6

Accommodations and board

The quality of the living accommodationsand board is very important for the moraleof the crew, and a crew with good moralewill often be more efficient. The site visit isa good opportunity to check the quality andprices of neighboring hotels or motels;prices are often negotiable for groups andextended periods of stay.

Several reputable hotel chains exist in Hol-land and it is never difficult to find suitableaccommodations except during holidays.The Ij Meer crossing was not conductednear a holiday, so accommodations wereeasy to find.

Planning and Estimating Costs

Size of the drilling rig and support equipment

The choice of rig is an important decision.The chart in Fig. 1.3indicates the pullingforce the rig should have for various diame-

ters and standard wall thicknesses of steelpipes relative to the length of the crossing.

In the Engineering chapter (Chapter 2), amore precise calculation of the pull force isexplained, which also takes into account an

eventual buoyancy control system.

Fig. 1.3. Size of the drilling rig.

Available torque is another important itemto consider when choosing a rig configura-tion for a particular job. Normally, highertorque is required when planning large-diameter hole-opening operations in soft or

hard ground and rock. Proper makeup andbreakout torque is the minimum

requiredtorque.

A rig should also have the power to turn ata specified rotary speed with specifiedtorque, without impacting the pulling orrotation specifications. Hole opening inrock requires higher rotary speeds insmaller sizes and lower rotary speeds inlarger sizes. If the correct rotary speed is

not maintained, lower penetration rates willresult.

A fast carriage travel speed is recom-mended when drilling in soft formations. It

is rarely necessary otherwise, but does savetime.

For the above reasons, sometimes only two(out of four) translation motors are used onthe maxi-rigs, thereby increasing the car-riage travel speed on crossings where amoderate pull force is expected, and one(out of two) rotation motor is used withdouble rotation speed on reaming smalldiameters in rock or hard formations.

40"

32"

36"

28"

24"

20"

16"

12"

5000

4500

4000

3500

3000

2500

2000

1500

1000

50 0

0

0 100 200 300 400 500 600 700 800 900 1 0 00 1 1 00 1 20 0 1 3 00 1 40 0 1 5 00

F (KN) (")

L (m)


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Planning and Scheduling: Planning and Estimating Costs

1-7

A midi-rig was too small so a maxi-rig was

chosen, using only two translation motors

and one rotation motor to increase effi-

ciency.

The project manager must now decide

upon the mud system, comprising a mixing

unit, mud pump(s), and recycling unit. In

the chapters on Steering (Chapter 3),

Reaming (Chapter 4), and Pullback (Chap-

ter 5),indication of flow rates are given, as

well as the theory behind them. A typical

maxi-rig is shown in Fig. 1.4.

For this project, one pumping skid wasused, delivering 140 cum/hr at 150 bars.Pumping rates would be as high as 100cum/hr during casing and reaming.

A standard mud mixing unit was chosen forthe rig side. In addition, mud was recycled,with one unit able to process 150 cum/hr of

mud with 25% cuttings on the rig side. Forthe reaming operations, a desanding unitwas placed at the pipe side for precleaning,and the mud with 4 to 7% cuttings waspumped back to the rig side with a pipelineservice pump through the 6-in. (150-mm)mud return line.

Fig. 1.4. Typical maxi-rig.

Drilling method and tools

At this stage, it is critical to understand thespecifics of the project and define the meth-ods. In particular, answer the followingquestions about the pilot hole, reaming,

pulling, and anchorage of the rig:

Pilot hole.

Should a jet or mud motor be used, andwhat type of bit is used?

Should a casing be used?

How many shifts per day will the crew

work?

In this project the decisions were to:

drill by jetting because of the soft, allu-

vial soils

use a 12-in. (300-mm) casing on thefirst 500 ft (150 m) to protect the entrycurve because of the length of thecrossing and soil conditions (morethan 3300 ft [1000 m] in alluvial mate-rials)

work the day shift until the casing isinstalled, and a double shift after that.


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1-8

Reaming.

Is it necessary to do pre-reaming?

What will be the final diameter of thereaming?

Will reaming be done with a fly cutter

or hole opener, and what types of cut-ters will be used?

How many passes will it take to reachthe final diameter?

Will reaming be done backward or for-ward?

How many and what size mud pumpswill be used?

Will a second rig or a winch be used toream in rock?

How many shifts per day will the crewwork?


execute a pre-reaming because of thefavorable soil conditions, movingdirectly to a 30-in. (760 mm) diameterwith a standard fly cutter reamer

bring a double quantity of drill pipe tofacilitate the pre-reaming

ream backward, pulling the reamer tothe rig, because of the space restric-tions on the pipe side; and because thelength of the crossing did not allow theuse of a side boom or dozer, but rathera winch with at least 50 tons of pullingcapacity

work a double shift because of thelength of the crossing and the alluvialsoil materials.

Pulling.

Should a buoyancy system be used?

Should a special reamer, such as agravel reamer, be used?

How much space is needed betweenrollers and how many rollers will be

used, or will a flotation ditch be used?

How many and what kind of supportswill be used for the catenary?

How many shifts per day will the crew

work?


use no buoyancy control systembecause of the small pipe diameter(less than 27.5 in. [700 mm])

use a standard bullet nose or fly cutterfor pulling, rather than a special tool(the final decision was left with thesuperintendent)

use 50 ft (15 m) between supports,thereby requiring 75 pipe rollers

fix the catenary to cross above theroad, and place rollers on top of thecontainers

be on alert to pull with a double shift,and to start pulling shortly after thereaming is finished.

Anchorage of rig. Because of the expectedpush/pull forces, is extra anchorageobtained by using a single-frame or double-frame sheet piling?

A single-frame sheet piling was installedbecause of the pull force necessary toremove the casing and pull back the 3821-ftx 16-in. (1165-m x 400-mm) pipeline.

Subcontracts

Civil works (access, site preparation, rein-statement) and pipeline prefabrication(stringing, welding, coating, testing) can behandled by the client when they are a pipe-line contractor or the pipeline division ofyour company. In this case, you have a con-tract for drilling services only.

Civil works can easily be integrated intothe scope of work in a turnkey contract. Inthese cases, the non-drilling aspects of ajob are often subcontracted to another com-pany or to another division of yourcompany. However, you can also decide toperform the access and site preparation onthe rig side when no major earth moving isinvolved.


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1-9

When choosing a subcontractor and negoti-

ating the subcontract, keep in mind that the

cheapest price might not always mean the

best deal. It is important to make certain

that work schedules are kept and that the

access is finished when the rig arrives, or

that the preliminary hydrotest and joint

coating are finished by the time reaming isstarted.

HDI was a subcontractor of A.Hak, and thecontract only included drilling services.Therefore, the only concern about civil andpipeline works was the timing of the opera-tions. Once A.Hak set the date when thepipeline would be ready for pulling, HDIworked backward to plan the mobilizationand drilling operations, and informed

A.Hak of the date when access and rig sitewould be ready for the rigs arrival.

Work schedule

Based on the above decisions about drillingmethods and tools, together with knowl-edge of usual progress rates for eachdrilling step and tool in similar soil condi-tions, it is now time make a tentative workschedule.

In this project the following was antici-pated:

two days for mobilizing all the equip-ment to the site

three days (three shifts) for rigging upthe rig and mud system

two days (two shifts) for drilling thefirst 1300 ft (400 m)

two days (two shifts) for installing500 ft (150 m) of 12-in. (300-mm) cas-ing

two days (four shifts) for drilling theremaining 2500 ft (765 m)

1/2 day (one shift) of slack time forpotential problems (shorts, mechani-cal failure, etc.)

1/2 day (one shift) for preparing thereaming (removing the spider subs,etc.)

1/2 day (one shift) for removing the 12-in. (300-mm) casing

1 1/2 day (three shifts) for reaming thehole and preparing for pulling

one day (two shifts) for pulling thepipe, with the second shift starting therig down

two days (two shifts) for rigging downand loading all the equipment

two days for demobilizing.

The totals were:

four days of transportation

five days of rig up/rig down (five shifts)

10 days of horizontal directional drill-ing (16 shifts).

Quantities

Crew. Once the basic decisions about thedrilling program are made (type of rig,method, and tentative schedule), it is time

to plan the crew. Typically, a crew workinga single shift consists of:

Midi-rig:

one superintendent

one driller

one surveyor

one mud engineer

one mechanic/pipe sider

one floormanfor a total of six crew

members on small crossings.

Maxi-rig:

one superintendent

one driller

one surveyor/assistant superintendent

one mud technician

one recycling technician


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1-10

one mechanic

one pipe sider/welder

two floormen

*

one operator (crane/excavator)for a

total of 10 crew members on large

crossings.

A large crew of 10 was planned for the dayshift and a smaller crew of eight for thenight shift (without a superintendent ormechanic).

Drilling accessories. In view of the mobili-zation, you must carefully plan thequantities of drilling accessories, consist-ing mainly of drill pipes and rollers.

This job required 75 pipe rollers, and 2 x1165/19.4 = 248 drill pipes with 5-in.diameters (plus a few spare pipestypi-

cally 10%).

Drilling consumables. An important partof the cost of an HDD project is the mudsystem. Tables compiled from experiencehelp estimate the quantity of bentoniterequired for a job of a given size (lengthand equivalent diameter), in given soil con-ditions (alluvium or rock), and with orwithout recycling (Table 1.1).

*For medium-sized crossings, the mud

technician can also do the recycling and

only one floorman is necessary, thus reduc-

ing the number of crew to eight.

Table 1.1. Bentonite consumption estimates.

Reaming in soft formations

Pipediameter

(mm)

Reaming sequence Finalreaming

(mm)

Holevolume

(l/m)

Withoutrecycling50 kg b/ft

Withrecycling50 kg b/ft

Ream #1

(mm)

Ream #2

(mm)

Ream #3

(mm)

Ream #4

(mm)

100 400 400 126 0.36 0.14

200 500 500 196 0.56 0.22

300 600 600 283 0.81 0.32

400 700 700 385 1.10 0.48

500 800 800 503 1.44 0.57

600 900 900 636 1.82 0.73

700 1000 1000 785 2.24 0.90

800 900 1100 1100 950 2.72 1.09

900 900 1200 1200 1131 3.23 1.29

1000 900 1400 1400 1539 4.40 1.76

1100 1000 1400 1500 1500 1767 5.05 2.02

1200 1000 1400 1600 1600 2011 5.74 2.30

Reaming in rock

Pipe

diameter(mm)

Reaming sequence Final

reaming(mm)

Hole

volume(l/m)

Without

recycling50 kg b/ft

With

recycling50 kg b/ft

Ream #1(mm)

Ream #2(mm)

Ream #3(mm)

Ream #4(mm)

100 437.5 437.5 150 1.72 0.57

200 437.5 437.5 150 1.72 0.57

300 437.5 650 650 332 3.79 1.26

400 437.5 650 650 332 3.79 1.26500 437.5 650 900 900 636 7.27 2.42

600 437.5 650 900 900 636 7.27 2.42

700 437.5 650 850 1000 1000 785 8.98 2.99

800 437.5 650 900 1100 1100 950 10.86 3.62

900 437.5 650 900 1200 1200 1131 12.93 4.31


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1-11

With a given quantity of bentonite, mix avolume of mud that, in cubic meters, isapproximately 14 to 17 times the tonnageof the bentonite. Out of this volume antici-pate that 2/3 will have to be treated ordisposed of after the project.

When there are a series of crossings in thesame area, it is also possible to plan vac-uum trucks and move the liquid mud fromone job to the next if the costs of removalare high. In this case, the project managershould think globally about his mudconsumption.

In this case, Table 1.1shows that with recy-cling, anticipate 0.48 x 50 kg x116510.3048 = 91,730 kg of bentonite willbe used, therefore mixing a total of 14 x57.333 = 1280 cum of mud. Approximately

213 x 1280 = 852 cum of used mud will beleft over at the end of the job.

If fresh water cannot be pumped from theriver, the total volume of water that must bepurchased is calculated the same way. Forpractical reasons, locate a source of freshwater that can deliver as much as 60 cum/hr; otherwise plan for storage water pits tobe sure that there is enough flow when youneed it (during casing and reaming).

Rig consumables and spares. The drillingspread should always travel with sufficientspare parts to remediate mechanical break-downs onsite and sufficient consumables(wire, grease for tool joints, hydraulic oil,etc.) for the job or series of jobs to be con-ducted. For estimating purposes use a dayrate, which is a daily average of the amountspent over a year.

Give special consideration to the quantityof fuel needed for the projecta midi-rig

spread uses an average of 300 gal (1150 l)per 12-hr shift, while a maxi-rig spreadwith complete pumping and recyclingcapabilities uses as much as 520 gal(2000 l) per 12-hr shift.

Mobilization/demobilization. When thetype of rig, type and number of pumps,type of recycling unit, and number of drillpipes and rollers have been decided, the

number of trucks necessary to mobilize thecomplete spread can be estimated. Ofcourse, the equipment might not all comefrom the same place, and considerationsother than the number of trucks are impor-tant when planning a mobilization. Theseother considerations will be reviewed later.

For this job the following was needed:

three tractors for the rig, mud tank,and power unit

one tractor and a flat-bed trailer forthe recycling unit

two tractors and a flat-bed trailer forthe control, workshop, spares, andcrew containers

three tractors and a flat-bed trailer forthe 75 rollers

one tractor and a flat-bed trailer forthe 500-ft x 12-in. (150-m x 300-mm)casing and the dead man

four tractors and a flat-bed trailer forthe 260 5-in. drill pipes and monels.

Another important consideration whenplanning a job is the time needed to mobi-lize the drilling spread. This obviously

affects the price, since this time cannot beused to work elsewhere and therefore rep-resents an opportunity cost. To reduce thiscost, plan the jobs so that the crossings per-formed in one region are completed oneafter the other during the same period ofthe year. Of course, this is often a questionof opportunities, but it is important to keepthis aspect of the planning in mind.

Furthermore, when planning and pricing ajob, consider the crew mobilization and

plan the relevant train or plane tickets andexpenses. Again, if crossings in the sameregion can be grouped, it is possible tomobilize a single crew for several jobs.

When bidding the Ij Meer crossing, a con-tract with another client was alreadysigned for two 30-in. (760-mm) crossingsin the Amsterdam region. So all three cross-ings were completed in the same timeframe using the same rig and crew.


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1-12

Other considerations

The following considerations are listed forcompleteness, since each project has itsown specifics (client, country of execution,financing).

Customs duties and taxes. Consider notonly the cost of these duties and taxes, butalso the time spent at the customs office.

Local taxes. Other taxes that may applywhen pricing a job include local incometaxes (which can sometimes take the formof a percentage of the turnover) or taxes onsalaries.

Insurance. In general, the drilling contrac-tor must present its own third-party liabilityinsurance. But quite often, a ConstructionAll Risk (CAR) policy is offered by the cli-ent or main contractor, since they havegreater bargaining power with the insur-ance company and can spread the risk on awider range of activities. If a CAR policy isnot offered by your client, you should thinkabout the cost of obtaining one before start-ing the project.

Weather conditions. Although the HDDmethod for river crossings is fairly inde-pendent of weather conditions, remember afew basic considerations when planning ajob:

If heavy rains are expected, pay atten-tion to preparing and maintaining theaccess roads and work areas during theproject.

If freezing is expected, daily progress

will be hampered by drainage proce-

dures for all the water lines and mud

lines at each end of day. Also, the

power unit must be protected from

excessive cold. One solution is to work

double shifts systematically, and installa tent with heaters on the power unit

for moderate cold (-10C [14F]). For

very cold and windy conditions, plan a

Sprung structure to protect the entire

drilling spread and crew.

Terms of payment. The terms of payment

will influence the cash flow of the project

and therefore will generate financial costs

or gains.

Bid bond. Some clients request a bid bond

to be deposited in a bank of their choice

before a drilling contractor can have his bid

considered at the price opening meeting.

This has a cost, although moderate.

Performance guarantee. Some clients ask

for a performance guarantee when award-

ing a job to a contractor; this also has a

cost.

Bank guarantee upon completion. It is

common that the final payment (5 or 10%)

is linked to the final acceptance of the

project. This payment is typically made

one year after the provisory acceptance,

unless a bank guarantee of the same

amount is arranged by the contractor for

the benefit of the client, with the corre-

sponding validity period; only then is the

final payment made at the time of the pro-visory acceptance. These costs should also

be considered.

Closing meeting

There should always be a closing meeting

initiated by the project manager with his

management. In this meeting, the project

and its context are presented, and the sell-

ing price and conditions are discussed and

agreed upon.


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1-14

field is the best training ground for direc-tional drilling.

Briefing the superintendent and assis-tant. Before the work starts, brief thesuperintendent and possibly his assistant orthe driller about the projectespeciallyabout the soil conditions. At this stage, theproject manager must be open to sugges-tions, new ideas, or requests for specificequipment coming from the superinten-dent. Practical considerations of thesuperintendent often save time and avoidinconveniences onsite during construction.

Transporting the crew. Prepare the final

mobilization plan of the crew(s) and inform

all personnel. Usually the drilling superin-

tendent is mobilized earlier to supervise the

preparatory activities at the site. Even if

these activities are not in the scope of work

but performed by the main contractor, the

superintendent must be onsite to coordinate

the effort. The superintendent also informs

the project manager about the progress to

correctly plan the equipment and crew

mobilization.

Consumables

Bentonite. Place orders for the supply ofbentonite. On large crossings with limitedworking space, you can plan a gradual

delivery to the site following the progressof the job, but only if the supplier is reli-able. Avoid being left on standby becausethe bentonite supply has been depleted.

Water. Check whether you need a permit topump in the river, and if you do need one,be sure that you have it. When loading theequipment on the trucks, check again thatthere is sufficient length of hoses to reachthe source of fresh water for mixing the

mud. If you have to buy the water, finalizethe contract now.

Fuel. Locate a local fuel supplier and final-ize a contract, stressing the importance ofregular deliveries. Again, avoid being onstandby because there is no fuel left on thejob.

Electric wire. Check the meterage of wirefor directional control. As explained inSteering (Chapter 3),always use new wireto try to eliminate the risk of electricalshorts when drilling the pilot hole.

Line of sight and coil installation

Before any onsite activity, make sure thatthe line of sight of the crossing and entryand exit points of the drilling are properlymarked. Entry and exit points should beidentified by the client and checked by thecrew surveyor. The surveyor will then placethe survey stakes, marking the line of sight

of the crossing. This must be completedbefore preparing the platform and installingthe sheet piling, to make sure that every-thing is properly placed.

The crew surveyor installs the coil whilethe rest of the crew is rigging up.

Subcontracts

Civil works. Most of the time, civil worksconsists only of preparing the final access

road for the rig (and pipe) site(s) and the

drilling platform, mud pits, and water pit,

when necessary. This must be ready before

the drilling and support equipment arrives.

The reinstatement will be done immedi-

ately after the tie in. As already mentioned,

the access road must be strong enough for

loads of 25 tons.

Very often, mud removal is part of anothersubcontract and is not performed by thecivil works company.

The subcontract for civil works must incor-porate the clients specifications forreinstatement. Also, since the HDD methodis environmentally friendly, reinstatementshould be done quickly and properly toleave a good impression of the river cross-ing method.


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Planning and Scheduling: Preparing to Work

1-15

Sheet piling for rig anchorage. When asheet piling is necessary, organize it a dayor two before the drilling equipment arrivesonsite. This work can be subcontracted.

Mud return line. When a mud return lineis necessary, make sure it is in place beforethe reaming operation begins. Try to installit before the rig arrives to make sure thatreaming activities will not be delayed oncethe pilot hole is finished. This preparationcan be subcontracted or executed by a fewcrew members mobilized early onsite.

Mud trucking. When a mud return linecannot be installed, for small crossings orwhen forward reaming is used, you canlocally hire a few vacuum trucks or farmtractors with tanks to move the drillingmud surfacing in the pipe side exit pit back

to the recycling unit located on the rig site.Finalize the contract with a service com-pany or local farmers, making sure it alsostates the working hours. Particularly,nighttime working hours should be sched-uled to ensure that the night crew has thesupport they need to continue working.

Pipeline prefabrication. Finalize the sub-contract for pipeline prefabrication (if any)at this stage, although probably much (suchas the choice of the subcontractor) has been

decided during the tender and negotiationphases of the main contract. Rememberthat good pipeline works are essential forthe success of the project. The client isinterested not only in a finished product,but in a finished product that is in goodworking condition. This means that thepipeline must withstand the expected pres-sures, maintain its circular shape, and havea proper coating. The best way to achievethis is to make sure that the prefabricatedpipeline fulfills these requirements beforeyou start the pulling operation.

Another important consideration whenfinalizing the subcontract is the respect ofthe work schedule. Avoid being on standbyafter the pilot hole because the pipeline isstill not tested or because the field jointcoating materials have not yet beendelivered.

In any case, clearly identify the limits ofthe subcontract and responsibilities. For

example, use a formal procedure, with anacceptance sheet, for delivering the pipe-line welded, tested, and coated to the drill-ing contractor; from this point the drillingcontractor is responsible for the pipeline.Also, make it clear who supplies and weldsthe pulling head (the design being, ofcourse, the responsibility of the drilling

company, unless stated otherwise).

The principle of a formal acceptance of thepipeline also applies when you are a sub-contractor of a pipeline main contractor.

Buoyancy control system. When a buoy-ancy control system is necessary, it alwaysremains under the direct responsibility ofthe HDD contractor. Even if the supply andinstallation are subcontracted, its constitu-ents and dimensions are engineered by the

drilling contractor, and the constructionshould be supervised by one of its crewmembers. At this stage of the project, it ismandatory to pass orders for the supply ofmaterials if they are not in stock, and planthe construction onsite.

Even if the system can be put into placeonly after the pipeline has been success-fully pretested, you can plan the materialsdelivery and some preparatory works (suchas double-jointing of HDPE pipes, con-structing the flanges) during the pipeline

prefabrication period.

Mud removal. Devise a good solution formud removal at this stage of the project. Ifleft until the end of the project, you mayfind yourself dealing with high prices andan unhappy client.

Since the inception of mud recycling tech-niques on directionally drilled crossingsthat use new light and mobile recyclingunits, there is usually little liquid mud to be

evacuated. In some cases, farmers mayallow you to spray the mud on their fields.

Dispose of the dry cuttings coming out ofthe hole (for a total equivalent to the vol-ume of the reamed hole), which have beenseparated from the mud. Often these cut-tings can be locally backfilled.

In all circumstances, obtain from the bento-nite supplier a composition certificate for


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1-16

his product. You may wish to conduct labo-ratory tests on mud samples to confirm thatit is harmless before locating a disposalarea.

As mentioned in the Drilling Consumablessection (page 1-10), when there are severalcrossings in the same region, liquid mudcan be moved from one site to the next withvacuum trucks or farm tractors with tanks,to create as little waste as possible.

Communications and coordination

It is very important to organize a good

communication system between the job site

and the outside world (phone, fax). This

will enable the site to inform its base regu-

larly about the progress of the project,

confirm orders for new deliveries of con-

sumables, request spare parts from the

base, discuss technical problems with other

specialized colleagues at the base, and

make faster and better decisions.

The progress of the subcontracts and deliv-ery of consumables during this preparatoryphase, as well as during construction, mustbe watched closely by the project manager.He is the central point of the project organi-zation through whom all communicationmust flow to make efficient decisions andadjustments. For a successful operation,you must establish a good working collabo-ration between the project manager and theconstruction superintendent.

Fig. 1.5. Typical marine installation.


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Chapter 2: Engineering

Generalities......................................................................................... 2-1

Presenting the engineering course .................................................................... 2-1Strength of materialsBackground ................................................................... 2-1

Basic strength of material ................................................................................................2-1Stresses combination ........................................................................................................2-2

Beam strength of materials...............................................................................................2-2

Beam/pipeline formulas....................................................................................................2-2

Pipeline Codes.................................................................................... 2-3

Definitions .......................................................................................................... 2-3Location classes................................................................................................. 2-3Construction types ............................................................................................. 2-3Pressures........................................................................................................... 2-5Design criteria .................................................................................................... 2-5

Stresses During Testing or Operations ........................................... 2-6

Hoop stress........................................................................................................ 2-6Bending stress ................................................................................................... 2-6Temperature stress............................................................................................ 2-6Restrained pipeline stress.................................................................................. 2-6Traction stress.................................................................................................... 2-6Ground pressure................................................................................................ 2-7Pipeline specifications........................................................................................ 2-7

Pipeline Engineering.......................................................................... 2-7Verifying wall thickness...................................................................................... 2-7

Hoop stress .......................................................................................................................2-7

Ground pressure...............................................................................................................2-8

Hydrostatic test .................................................................................................. 2-9Operating pressure .......................................................................................... 2-10Comments........................................................................................................ 2-10Installation conditions....................................................................................... 2-10Minimum radius................................................................................................ 2-10

Crossing Engineering...................................................................... 2-11Introduction ...................................................................................................... 2-11The crossings path design .............................................................................. 2-11

River ...............................................................................................................................2-11

Exclusion area................................................................................................................2-11

Entry angle .....................................................................................................................2-12

Exit angle........................................................................................................................2-12

Subsoil nature or obstacles ............................................................................................2-12

Design of the profile .......................................................................................................2-12


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ii

The crossings layout........................................................................................2-15Entry side ....................................................................................................................... 2-15

Pipe side......................................................................................................................... 2-16

Catenary......................................................................................................................... 2-18

Engineering Procedures ..................................................................2-19

Preliminary evaluation ......................................................................................2-19Product line nature ........................................................................................................ 2-19

Pipe size ......................................................................................................................... 2-19

Pipe length ..................................................................................................................... 2-19

Pipe mechanical characteristics .................................................................................... 2-20

Pipeline coating and field joints .................................................................................... 2-20

Catenary...........................................................................................................2-21

Multiple pipeline installation.


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iii

List of Figures

Fig. 2.1. Stress-strain curve. .............................................................................................2-1

Fig. 2.2. Determining the exclusion area........................................................................2-12

Fig. 2.3. Designing the pilot hole profile........................................................................2-13

Fig. 2.4. Crossings profile: minimum depth. ................................................................2-14

Fig. 2.5. Crossings profile: minimum length. ...............................................................2-14Fig. 2.6. Typical entry side layout..................................................................................2-16

Fig. 2.7. Typical pipe side layout. ..................................................................................2-17

Fig. 2.8. Pipe side, South Louisiana, USA. ....................................................................2-17

Fig. 2.9. Catenary with and without an exit pit. .............................................................2-18

Fig. 2.10. Length/diameter feasibility range. .................................................................2-20

Fig. 2.11. Catenary. ........................................................................................................2-22

Fig. 2.12. Pipeline string and catenary. Norfolk, Virginia, USA. ..................................2-22

List of Tables

Table 2.1. API pipeline specifications. .............................................................................2-3

Table 2.2. Classification of steel pipe construction (API Table 841.15A)........................2-4

Table 2.3. Values of design factor F (API Table 841.1A).................................................2-5

Table 2.4. Longitudinal joint factor E (API Table 841.1B). .............................................2-8

Table 2.5. Temperature derating factor T (API Table 841.1C). ........................................2-9

Maxi-rig, Southeast Texas, USA.


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iv

Notes


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Chapter 2: Engineering

Generalities

Presenting the engineering course

This chapter reviews the objectives of hori-zontal directional drilling (HDD)engineering and the course plan of themodules dealing with engineering. Theengineering exercises are aimed towardissuing a recommendation on the feasibilityof an HDD crossing with regard to techni-cal, scheduling, and economical criteria,and defining the crossings acceptancecriteria.

It is assumed that the engineer has the fol-lowing minimum information:

pipeline characteristics

pipeline route

obstacle profile

subsoil conditions.

Strengthof materialsBackground

Basic strength of material. The strength ofa material depends on the relationshipbetween external forces applied to elasticbodies and the resulting deformations andstresses. Forces on pipelines are producedby gravity, buoyancy (if any), pulling onthe pipe, bending the pipe, soil reaction(friction), and internal hydrostatic pressure.Many mechanical properties of materialsare determined by testing, which gives therelationship between stresses and strains,

as is explained in the following section.Stress is the force per unit area and isexpressed in lb/in.2 (Newton/m2 or Pascal[Pa]). The megapascal (Mpa) is often usedas a convenient multiple of the Pascal. Ifthe stress tends to stretch the material, it iscalled a tensile stress; if it compresses orshortens the material, it is a compressive

stress. By convention, a tensile stress isnegative.

Unit strain (or strain) is the amount bywhich a dimension of a body changes whenthe body is submitted to a load, divided bythe original value of the dimension. Whenthe load varies, you plot a curve showingstrain vs. stress. Usually, this curve is linearuntil a limit called the proportional limit isreached. Elastic limitis the maximum stress

under which a test specimen may be sub-jected and still return to its original lengthwhen the load is released. If the stressexceeds this elastic limit, the material issaid to be stressed in the plastic regionwhere permanent deformation occurs, untilthe ultimate strength is reached, when thematerial breaks (Fig. 2.1)

Fig. 2.1. Stress-strain curve.

1 = Strain

2 = Stress

3 = Proportional limit

4 = Elastic limit

5 = Ultimate limit

34

5

2

1


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2-2

The modulus of elasticity E, also calledYoungs modulus, is the ratio of unit stressto unit strain, within the proportional limit.

When a material is subjected to a longitudi-nal strain within the proportional limit,there is a lateral strain that is proportional

to the longitudinal strain. The ratio is calledPoissons ratio. It is important to under-stand that if a material is not allowed tostrain in one direction, the strain in theother direction induces stresses in thematerial.

For example, during pressure testing of apipeline, if the pipeline section is restrainedfrom shortening, you will observe a tensilestress in the pipeline equal to the tensilestress that results from pressure multipliedby Poissons ratio. The values of E and

for steel are:

Poissons ratio: steel= 0.3

Youngs modulus: Esteel= 2.1 105Mpa

or 2.1 107T/m2

Stresses combination. Stresses cannot sim-ply be added if they occur in differentdirections. For example, if a material is

subjected to two perpendicular stresses,both compressive or both tensile, it willbreak or reach the plastic region longbefore the same material is subjected to thesame stresses with one being compressiveand the other tensile. When discussingPoissons ratio, it was stated that a materialthat was subjected to tensile stress wouldshrink in the other direction. If the materialis subjected to a tensile stress in that direc-tion, the action of this tensile stress is verydestructive on the material that would oth-erwise shrink.

Different formulas are used to combinestresses. The formulas will not be derivedhere, since that is beyond the scope of thiscourse. They will only be mentioned whennecessary.

Beam strength of materials. When consid-ering the strength of materials, a pipeline isequivalent to a beam, having a constant

section. For beam calculations, you mustdetermine at any pointxthe moment of allforces applied to the beam, either at theright or left of that pointx. These two val-ues are equal in static equilibrium;therefore, use the one that is easiest tocalculate.

If a beam is subjected to a longitudinal(pulling) force, the stress caused by the Fxcomponent of the force Fis:

If M(x) is the moment of a straight and hor-izontal beam, then the deformation of thebeam can be calculated by resolving thefollowing differential equation:

The stress due to moment M is tensile orcompressive, depending on the orientationof the moment and the point in the beammaterial that is considered. The maximumstress is on the upper and lower fiber of thebeam, and equal to:

Beam/pipeline formulas. With the nota-tions:

D = outside diameter in m

d = inside diameter in m

e = wall thickness in m

E = modulus of elasticity

l = length

you have the following values:

Section Area A = (D2- d2)/4

= e(D - e)

Section Inertia I = (D4- d4)/64

FxA-----=

d2y

dx2

--------M x( )

EI-------------=

MxD

2l-------------=


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2-4

Table 2.2. Classification of steel pipe construction (API Table 841.15A).

CharacteristicsDesign Factor F

Type AConstruction

0.72

Type BConstruction

0.60

Type CConstruction

0.5

Type DConstruction

0.40

Location where typeof construction will beused

A. On privaterights-of-way inClass 1 locations



A. All in Class 4locations

B. Parallel

encroachmentson:1) Privately owned

roads in Class 1locations

2) Unimprovedroads in Class 1locations

B. Parallel


roads in Class2 locations

2) Unimprovedroads in Class2 locations

3) Hard-surfacedroads, high-ways, or publicstreets and rail-roads in Class1 and 2 loca-tions

B. Parallel


roads in Class3 locations

2) Unimprovedroads in Class3 locations

3) Hard-surfacedroads, high-ways, or publicstreets and rail-roads in Class3 locations

C. Crossings with-

out casings on pri-vately ownedroads in Class 1locations

C. Crossings with-

out casings on:1) Privately ownedroads in Class2 locations

2) Unimprovedpublic roads inClass 1 and 2locations

3) Hard-surfacedroads, high-ways or publicstreets and rail-roads in Class1 locations

C. Crossings with-

out casings on:1) Privately ownedroads in Class3 locations

2) Unimprovedpublic roads inClass 3 loca-tions

3) Hard-surfacedroads, high-ways, or publicstreets and rail-roads in Class2 and 3 loca-tions

D. Crossings withcasings on unim-

proved roads,hard-surfacedroads, highways,or public streetsand railroads inClass 1 locations

D. Crossing withcasings on hard-

surfaced roads,highways, or pub-lic streets and rail-roads in Class 2locations

D. Compressorstation piping

E. On bridges inClass 1 and 2locations

E. Offshore plat-form piping,including risers,and for a distanceof 5 pipe diame-ters beyond thebottom elbow,bend or fitting.Transition pieces

at the end of thispipe are not con-sidered fittings.

F. Fabricatedassemblies pipe-lines in Class 1and 2 locations

F. Near inhabitedareas in Class 1and 2 locations


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Engineering: Pipeline Codes

2-5

Usually, Type A construction applies toClass 1 location, Type B to Class 2, and soon, but there are many exceptions stated inthis table. Therefore, each section of thepipeline is given a type, which determinesthe factor F to be applied at the designstage, as follows (Table 2.3; ANSI B 31-4-1982 Table 841.1A):

Pressures

Maximum operating pressure is the valueof the maximum pressure in the pipelineduring operation. It is the lowest value ofthe design pressure and the test pressuredivided by:

1.1 for Class 1

1.25 for Class 21.4 for Class 3

1.4 for Class 4.

Design pressure was previously defined asthe value of the pressure, greater than oper-ating pressure, that is used to design thepipeline. Test pressure varies with pipelineclass, as follows:

Class 1: (1.1*Maximum operating pressure)



Class 4: (1.4*Maximum operating pressure).

The test is carried out with water. The max-imum operating pressure and designpressure have a single value for the entirepipeline. The test pressure, on the otherhand, varies with pipeline class. Each sec-tion of the same class is tested separately,and a general test is carried out at the endof construction according to the above-mentioned coefficients, using a test pres-sure that does not overstress the pipeline.

Design criteria

The engineer must first determine the con-struction type that is most applicable to thecrossing. Based on horizontal drillingexperience, an HDD crossing can be TypeA with a design factor Fequal to 0.72 if theland section on both sides of the crossing isalso Type A. In fact, the river section issafer than the land section because there isno risk of human interference. Therefore,whenever the local regulations or lawsallow it, try to use the same classificationfor the crossing as for the land line.

This is important, because you must use thedesign factor Fto verify that the pipe is not

overstressed in different situations during

construction and operation. Stresses may

be caused by pressure inside the pipeline

(during testing or operations), pressure out-

side the pipeline (including ground

pressure), temperature variations, bending

the pipeline in the hole (during testing or

operations), or bending the pipeline out of

the hole (during installation).

Table 2.3. Values of design factor F(API Table 841.1A).

Construction

Types(see 841.151)

DesignFactor F

Type A 0.72

Type B 0.60

Type C 0.50Type D 0.40


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Engineering: Pipeline Engineering

2-7

Ground pressure

When the pipeline cover is important, andwhen the soil cohesion is low, you mustconsider the weight of the ground on top ofthe pipeline. The following formula, takenfrom Dreyfuss (Thin metallic conducts

under roads and railways, Technip Edi-tion), can be used to estimate groundpressureg:

where

= ground specific weight

h = depth of top of pipe.

When the D/t ratio is high, there is a risk ofelastic instability. Elastic instabilityis whena body collapses even though the loadapplied to this body does not create stressesin excess of yield. This is because the stress

formulas assume that the load is perfectlycentered and that the pipe is perfectlyround. The critical value for external pres-sure on a pipe is given by the formula:

where Ptcis the critical external pressure.

Pipeline specifications

API specifications 5L, 5LX and 5LS firststated the chemical requirements of steelused for seamless or welded pipeline. Theminimum yield limit (SMYS), minimumultimate tensile stress, and minimum per-centage of elongation are also specified, asare tolerances on dimensions and weight.

The API grades and corresponding SMYSare given in Table 2.1 (metric and USunits). Some of the grades may not be usedin certain areas, especially when very lowtemperatures are expected.

Pipeline Engineering

Verifying wall thickness

The engineer must first check that the wallthickness of the pipeline is sufficient withrespect to working pressure.

Hoop stress. Hoop stress was previouslydefined as the stress caused by internalpressure in the pipeline during testing or

operations. The formula for that calculationis given in ANSI B 31-8:

where

P = design pressure

S = SMYS

t = nominal pipe wall thickness

D = nominal pipe diameter

F = design factor

E = longitudinal joint factor

T = temperature derating factor.

The values of factors F, Eand Tare givenby ANSI B31.8-1982, in Tables 841.1A,841.1B, and 841.1C, respectively (repro-duced here as Table 2.3, Table 2.4, andTable 2.5, respectively). This is the Barlowformula used to determine the strength ofmaterials (Bending Stress, page 2-6),where the hoop stress Hmust not exceedSMYS x FxEx T. Please note thatDis thenominal diameterof the pipeline.

g 0.4hD

t2----=

Ptc2E

1 2--------------

1

D

t----

D

t---- 1

2

--------------------------=

P 2St

D----- F E T=


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2-8

Ground pressure. If pipeline cover is

important, you must check that the pipeline

will not collapse because of external pres-

sure. The formula mentioned in Ground

Pressure (page 2-7) should be used:

where

= ground specific weight

h = depth of top of pipe

If the calculated stress exceeds 70% ofSMYS, then proceed with a detailed analy-sis of collapse and out-of-roundness risks.The elastic instability should also be

checked because a high D/t ratio increasesthis risk. The critical external pressure Ptcmust be more than four times the externalpressure.

*Includes Classes 12, 22, 32, 42, and 52 only (definitions for the various classes of welded pipe are

given in 804.243).

g 0.4hD

t2----=

Table 2.4. Longitudinal joint factor E (API Table 841.1B).

Spec Number Pipe Class E Factor

ASTM A53

Seamless

Electric Resistance Welded

Furnace Welded

1.00

1.00

0.60

ASTM A106 Seamless 1.00

ASTM A134 Electric Fusion Arc Welded 0.80

ASTM A135 Electric Resistance Welded 1.00

ASTM A139 Electric Fusion Welded 0.80

ASTM A211 Spiral Welded Steel Pipe 0.80

ASTM A381 Double Submerged Arc

Welded 1.00

ASTM A671 Electric Fusion Welded 1.00*

ASTM A672 Electric Fusion Welded 1.00*

API 5 L

Seamless


Electric Flash Welded

Submerged Arc Welded

Furnace Butt Welded

1.00

1.00

1.00

1.00

0.60

API 5 LX

Seamless


Electric Flash Welded


1.00

1.00

1.00

1.00

API 5LS Electric Resistance Welded


1.00

1.00


37/188

Engineering: Pipeline Engineering

2-9

Hydrostatic test

In Pressures (page 2-5) it was stated thatthe test pressure is equal to the maximumoperating pressure multiplied by a coeffi-cient that varies with pipeline classlocation:




Class 4: (1.4*Maximum operating pressure).

Maximum allowable operating pressure isalso equal to the lowest of design pressureand test pressure divided by the abovecoefficients.

However, the installed pipeline is also sub-jected to bending stress (page 2-6) due tocurves in the reamed hole, whether inten-

tional or not. A residual traction (page 2-6)may increase the longitudinal stress and therestrained pipeline stress (page 2-6). Thesestresses can be calculated as follows:

Hoop stress: H= PD/2t

Residual traction: 0= Pr/(t(D-t))

Bending stress: b= ED/2R

Restrained pipe: r= -H

Longitudinal stress: a= - |0| -|H|

Generally, the residual traction Pr is negli-

gible and the residual stress 0 can beconsidered zero, so essentially you have acombination of longitudinal and hoopstress. The Von Mises criteriais commonlyused for these stress combinations. The

combined stress is equal to:

2= (H2 + L

2 - HL+ 3s)

where sis the shear stress. In this case theshear stress is negligible, and the aboveequation can be reduced to:

2= (H2 + L

2 - HL)

where

L= ab

This equivalent stress must be less thanor equal to 95% of SMYS. Since the bend-ing stress varies with the bending radius,this formula will give a minimum bendingradius due to hydrostatic test Rtest.

Table 2.5. Temperature derating factor T (API Table 841.1C).

Temperature FTemperature Derating

Factor T

250 or less 1.000

300 0.967

350 0.933

400 0.900

450 0.867Note: The conversion between F and C is C = 5/9 (F + 32).

Therefore, the above temperatures C equivalents are:

F C

250 121.1

300 148.9

350 176.7

400 204.4

450 232.2


38/188


2-10

Operating pressure

The ANSI B31.8 article 833.4 specifies thatcombined stress due to expansion, longitu-dinal pressure, and longitudinal flexionmust not exceed SMYS, and that the sumof longitudinal pressure and longitudinalflexion must not exceed 75% of SMYS.

For pipes installed by HDD, assuming thathole diameter is closed from the pipes out-side diameter (OD), the combinedexpansion stress is negligible if the soilresists lateral movements of the pipe and ifthe pipe is not subjected to torsion duringpulling. In that case, you only need tocheck that:

|a| + |b| 0.75 x SMYS x F x T

where

a= 0-Pi/2t

b= ED/2R

Pi= Maximum operating pressure.

The minimum radius due to operating con-ditions can be calculated and is equal toRoper. However, if the temperature of the

fluid carried by the pipeline is high, ANSIB31.4 article 419.6.4 applies, with a longi-tudinal stress equal to:

a= ET - |0| - |H| + |b|

where T is the difference between themaximum operating temperature and the

installation temperature.

Comments

The above calculations apply to pipelineinstalled with the HDD method only. Thesoil should be strong and stable; additionalengineering is required for very soft ormuddy soils, seismic areas, and zones sub-

ject to ground slippage. This additionalengineering is beyond the scope of thischapter because it is based on standardpipeline engineering.

Installation conditions

During installation, the pipeline is subject

to traction forces, balance by ground fric-tion into the hole or on the rollers, and bybending according to drilled path profile.You must estimate the pulling force tocheck that the pipe will not be overstressed.In addition, the pipe is generally laid hori-zontally on rollers or in a flotation ditch.Since the pilot hole exits at an angle, thepipe must be handled so that it enters theground with an equivalent angle. This iswhat is called the catenary. The pulling

force estimation and catenary calculation

will be explained later, and for now assumethan the pulling force PFisknown.

The longitudinal stress adue to PF mustbe less than 95% of SMYS. Accordingly,calculate the minimum radius during pull-ing of the pipe Rpull:

a= PF/(t(D-t)) ED/2R 0.95 SMYS

Minimum radius

You have determined the minimum radiusfor various conditions. The minimumradius of the crossing must be the greatestof:

Minimum radius during testing: Rtest

Minimum radius during operation:

Roper

Minimum radius during installation:

Rpull

However, there may be other situationswhere you would use a higher radius thanthis. First, the pilot hole cannot be drilledperfectly. Use a coefficient to allow forunexpected variations in hole profile and tomake sure that the radius cannot be less


39/188

Engineering: Crossing Engineering

2-11

than the minimum. Second, the radius is animportant factor for pull force value. For alarge pipeline, use a higher radius to reduce

the anticipated pull force. The relationshipbetween radius and pulling force will bedescribed later.

Crossing Engineering

Introduction

You now have the basic engineering infor-mation required to design a crossing. Youknow how to determine the minimumallowable radius and how to verify that thepipe wall thickness is acceptable for HDD.

However, this is still not enough. The vari-ous parameters you must understand and

use to design a crossing and determine

whether it is feasible will now be reviewed.

First, you will learn how to design the

crossings profile based on the minimum

radius and exclusion area. Then the layout

on both sides of the river and the necessary

resources you must have are described.

The crossings path design

River. The basic information you will needis a profile of the river. Particularly, youshould obtain the current profile of theriversome rivers may change during ayears time, so old profiles must be usedand checked very carefully.

It may sometimes be difficult to determinewhere the river bottom is, especially whenthe river is subject to scouring. The scour-ing level must be estimated according tothe rivers hydrologic data.

You must also determine where the riverbanks are, because the river can shift fromtime to time, especially after a flood. In thatcase, the banks may be the limits of theflood area, or any other point within theselimits where you can be sure that the riverwill not shift and expose the pipeline.

There may be obstacles in the bed of theriver, such as bridge piers, which maycause problems when the river flow is very

high. There may also be an existing naviga-tion channel or one planned for the future.If the river is dredged, you must leave anallowance for the dredge below the nomi-nal dredging depth.

Exclusion area. At this stage, you shouldknow the pipe and entry sides, the watersource, the quality of the water, the riverbottoms location, and the location of itsbanks. These data are sufficient to start

drafting a tentative profile of the crossing.

On a drawing of the rivers profile, markthe dredging limit (if any), the scour level(if any), and the real banks of the river. Thearea delimited by the verticals from thebanks and the lowest of river bottom, scourlevel and dredging area, plus minimumpipeline cover, is called the exclusion area.This defines a rectangular area (Fig. 2.2)where the pipeline must not be installed.


40/188


2-12

Fig. 2.2. Determining the exclusion area.

If the river is very stable, the bottom line ofthe exclusion area may follow the riversbottom (i.e., parallel at a distance equal tominimum pipeline cover).

Minimum pipeline coverrefers to the mini-mum soil height that must cover the pipe tomake sure that it will not rise toward thesurface when it is empty. Generally, about15 ft (5 m) are sufficient. This can bereduced somewhat in rock or hard forma-tion, but you also must remember thatpilothole drilling is not that accurate. You can

add a drilling safety margin to the mini-mum cover, which should be 2 to 5 ft (1 to2 m), according to the crossings length.

The basic data for a crossings design arethe exclusion area parameters discussedabove. However, there may be anotherrestriction, which is the maximum groundcover that is allowed above the pipe. It waspreviously mentioned that ground pressure(page 2-7) could be a problem. In that case,the formula will give you a maximumcover on top of the pipe. Mark that limit on

the profiles drawing, which will be a hori-zontal line called bottom limit.

There may be another reason to have a bot-tom limit: there may be bedrock, a hardformation, or a gravel area that you want toavoid. At this stage of the engineering ofthe crossing, you may not know exactlywhere that limit is. You can desi

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