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INTRODUCTION TO PIPELINE DESIGN

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Module Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SECTION 1 – PIPELINE DESIGN FUNDAMENTALSIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Key Pipeline Design Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Determining Loss of Pressure Due to Friction . . . . . . . . . . . . . . . . . . . . . . . 5

Review 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

SECTION 2 – PIPE SIZE OPTIMIZATIONIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Pipe Sizing & Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Pipeline Capacity Expansion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Capacity Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Review 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

SECTION 3 – PIPE WALL THICKNESS CALCULATIONSIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Pipe Wall Thickness Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Design Pressure Formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Review 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

SECTION 4 – PIPELINE COSTSIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Cost of Gas Transmission Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Review 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

ANSWERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26



PLEASE NOTEOperations personnel use a combination of skill, knowledge, and

technology to accomplish specific goals. A key objective of the Gas

Controller Training Program is to promote an understanding of

theoretical basis for operational decisions used on the job every day. This

training program enhances job-related skills by providing relevant and

current information with immediate application for employees.

Information contained in the modules is theoretical. A foundation of

basic information facilitates an understanding of technology and its

application. Every effort has been made to reflect pure scientific

principles in the training program. Nevertheless, in some cases, pure

theory conflicts with the practical realities of daily operations.

Usefulness to the employee is our most important priority during the

development of the materials in the Gas Controller Training Program.

INTRODUCTION TO PIPELINE DESIGNGAS CONTROLLER TRAINING PROGRAM

© 2002 ENBRIDGE TECHNOLOGY INC.

Reproduction Prohibited

ENBRIDGE TECHNOLOGY INC.

Suite 60, PO Box 398

10201 Jasper Avenue

Edmonton, Alberta

Canada T5J 2J9

Telephone +1 - 780-412-6469

Fax +1 - 780-412-6460

Reference: G0.6 Introduction to Pipeline Design – APRIL 2003



STUDY SKILLSEach of the modules in the Gas Controller Training Program is

designed in a performance based self-instructional format. This

means that you are responsible for your own learning and for

ensuring that you are ready to demonstrate your knowledge and

skills. Our focus is on the performance of the necessary skills and

demonstration of the knowledge needed to perform your job.

1. The modules are designed for short but concentrated periods of

study from ten to forty-five minutes each. Remember that

generally one week of self-study replaces 10 hours of in-classattendance. For example, if you have a three week self-study

block, then you have to account for 30 hours of study time if you

want to keep pace with most learning programs.

2. When you are studying the module, look for connections between

the information presented and your responsibilities on the job. The

more connections you can make, the better you will be able to

recall.

3. There are self-tests at the end of each section in the module.

Habitually completing these tests will ensure your knowledge of

the information. Use the test to measure your understanding. If you

have an incorrect answer, check the information in the section of

the module to find out why the error was made. Remember, you

are responsible for your own performance.

4. Start studying each section of the module by reading the objectives

and the introduction. This provides both the focus for your

learning and a preview of the test items.

5. Each module is prepared to adapt to a number of different learning

styles. Some learners will proceed directly from the introduction

and objectives to the review questions. Then they will study any

topic that is missed. Most learners, however, work from the

introduction through to the end of the text in a systematic way.Whichever way you choose to learn, you are free to use the

materials as you see fit.



6. Every module has a performance based test. Each item in the testis related to an objective for each section. To prepare for the test,

you should ensure that all section reviews are completed and

understood. Many learners review the material in the module

before taking the test.

7. To aid your understanding and enhance your time in the learning

activities, new terms, concepts and principles are printed in bold

face along with their definition highlighted in italics. These are

also listed in the Glossary supplied at the end of the module.

8. Many learners have had success by reading the module Summary

and Glossary. Items in the Glossary are cross-referenced to the

place in the module where they were first introduced. This way, if there is a topic or a definition that you do not recognize, you can

easily find it in the module.



Introduction to Pipeline Design is an overview of the modules GAS

PIPELINE DESIGN FUNDAMENTALS, HYDRAULICS LEVEL I, and other

modules dealing with gas pipeline design. The detailed modules are

theoretical in nature and provide Controllers with comprehensive and

detailed knowledge of the design issues that affect their ability to

maintain a safe and efficient pipeline operation. Many modules

provide concrete examples of calculations and formulas commonly

used in advanced pipeline design. Because this module is intended as a

general overview, these formulas and calculations are not providedhere. Rather, readers should refer to the specific module in question

for more information.

This module provides information on the following goals.

• It provides a general overview of pipeline design.

• It explains the relationship between volume and pressure in a

pipeline.

• It describes how pipeline size and wall thickness are selected.• It explains the key factors that influence pipeline costs.

None

1


MODULE GOALS

INTRODUCTION

PREREQUISITES



3


This section of the module provides a general description of how

friction caused by gas flowing in a pipe affects pipeline pressures.

This section also describes how the pressure loss can be determined.

Readers should note that the module PIPELINE DESIGN FUNDAMENTALS

contains an extensive appendix that provides numerous exampleswhich use the following equations and numbers to solve pipeline

design problems:

• the Reynolds Number

• the Moody Diagram

• the Steady State Equation

• the Total Energy Equation.

For more information, readers should refer to the module – PIPELINE

DESIGN FUNDAMENTALS.

After this section, you will be able to complete the following

objectives.

• Describe the three major gas pipeline design parameters.

• Explain which pipe characteristics and gas properties are important

in pipeline design.

• Understand how to determine pressure loss due to friction in a gas

pipeline.

PIPELINE DESIGN FUNDAMENTALS

INTRODUCTION

OBJECTIVES

SECTION 1



4

GAS CONTROLLER TRAINING PROGRAM

Pipeline design involves a number of progressive steps using basicscientific laws and equations for calculations to determine optimum

size and operating characteristics of a pipeline system. It is necessary

to understand the conditions that affect the gas in the pipeline in

order to design it properly. In addition, the following parameters

must be considered in pipeline design: pipeline characteristics,

physical properties of the gas, and the relationship between the pipe

and the gas.

The physical characteristics of the pipe affect how a gas will behave

in a pipeline. Specifically, three pipe parameters must be considered

in design:

• pipe inside diameter (ID)

• pipe length (L) and

• relative roughness of internal pipe wall surface.

Figure 1Pipe CharacteristicsPipe inside diameter, pipe wall roughness and pipe length affect how a gas

will behave in a pipeline.

Along with the characteristics of the pipe, the physical properties of

the gas affect the design of the pipeline. There are four properties of

gas that must be considered:

• natural gas liquids (NGL) or liquefied propane gas (LPG) andmoisture content

• density or specific gravity

• compressibility, and

• temperature.

KEY PIPELINEDESIGN

PARAMETERS

PIPELINE

CHARACTERISTICS

Length

Wall Roughness

InsideDiameter

PHYSICAL PROPERTIESOF THE GAS



Pipe diameter, gas viscosity, and velocity combine to affect flow. Theinterdependence between the pipe diameter, liquid viscosity, and flow

viscosity is defined by a mathematical relationship called the

Reynolds number, Re. The Reynolds number is used to describe the

type of flow exhibited by a particular gas flowing through a pipe of a

specific dimension (see Figure 2).

Figure 2 The Reynolds Number The Reynolds Number is used to describe the type of flow in a pipe.

The first step in determining pressure loss due to friction is to calculate

the Reynolds Number. After the Reynolds number is calculated, there

are two additional steps required to calculate the pressure loss: a

Moody Diagram is used to determine a friction factor; then a Steady

State Flow Equation is used to calculate the pressure loss.

The value of the Reynolds Number determines if the type of flow in

a pipe is laminar, critical, or turbulent. Refer to the module P IPELINE

DESIGN FUNDAMENTALS for detailed instructions on calculating the

Reynolds number.

The friction factor can be read from a Moody Diagram. The Moody

Diagram is a graphical representation of friction factors for a series

of related flow conditions. These curves relate two dimensionless

parameters (the Reynolds number and the relative roughness of the

inside pipe wall) to the friction factor (see Figure 4).

Figure 3Turbulent Flow The relative roughness and Reynolds Number are used to find the friction

factor.

5


THE RELATIONSHIPBETWEEN THE PIPE &THE GAS

Friction, n

Re D × v

n=

Diameter Velocity, v

DETERMININGLOSS OFPRESSURE DUE

TO FRICTION

STEP 1 – CALCULATETHE REYNOLDSNUMBER, (RE)

STEP 2 – DETERMINETHE FRICTIONFACTOR, (F)

Turbulent



6


Flow in vhich the gas in the center of the pipe moves faster than the gas near the pipe walls is called laminar flow. If there is laminar

flow, minimal mixing of gas occurs and the friction factor can be

read from the Moody Diagram. For laminar flow there is a linear

relationship between the Reynolds Number and the friction factor.

If flow is turbulent, the friction factor is also found using the Moody

Diagram. However, with turbulent flow, the relative roughness must

also be taken into account so that the correct curve is used (see

Figure 4). Under normal pipeline operating conditions, the flow is

turbulent.

Figure 4Moody Diagram

A general steady-state flow equation has been developed from an

energy balance over a pipeline. Steady State is a state or condition of

a system, such as a pipeline, that stays constant or does not change

over time. This equation and its derivation is defined in most texts on

fluid mechanics and thermodynamics.

Several pipeline flow equations have been developed for different flow

conditions and pipeline diameters. Some examples are Weymouth,

Panhandle A & B, and AGA flow formulas. These formulas contain

adjustment factors that are found in practice and are specific to local

field conditions. These flow formulas are used to predict pressure

drops at differing flow rates with various sizes of pipe.

STEP 3 – CALCULATETHE PRESSURE LOSS

USING FLOWEQUATIONS



7


1. What are the three pipe characteristics that must beconsidered in pipeline design?

a) Inside diameter, wall thickness, and relative roughness of

internal wall surface

b) Outside diameter, wall thickness, and relative roughness of

internal wall surface

c) Inside diameter, length, relative roughness of internal wall

surface

d) Outside diameter, length, relative roughness of internal wall

surface

2. The Reynolds number describes which of the following?

a) It relates the characteristics of the pipe and the fluid flowing

through it

b) It is dimensionless (i.e., has no units of measurement)

c) It describes the type of flow for a gas flowing through a

specific pipe

d) All of the above

3. For laminar flow, there is a linear relationship between theReynolds Number and the friction factor.

a) True

b) False

4. What is the flow under normal gas transmission pipelineoperating conditions called?

a) It is laminar

b) It is turbulent

c) It is critical

d) All of the above

Answers are at the end of this module.

SECTION 2

REVIEW 1



9


SECTION 2

Most pipelines are designed using computer programs to process the

basic pipeline flow equations. Computers allow us to look quickly at

many different alternatives with respect to pipeline size, temperature,

pressure, and volumes. However, in order to understand computer

calculations, a basic understanding of universal gas laws is required.

This section of the module provides an overview of the concepts of energy conservation in relation to the practice of pipeline design.

This section also discusses the importance of determining optimum

pipe size, volume capacity, line pressure, and other related criteria for

pipeline design.

The module PIPELINE DESIGN FUNDAMENTALS provides numerous

practical examples of typical problems related to the application of

universal gas theory as well as pipe design pressure calculations. To

see these examples and calculations, readers should refer to those

modules and also to the WORKBOOK , which is a collection of

problems designed to show the application of universal gas laws to

pipeline design.


objectives.

• Identify the main factors affecting pipeline design.

• Describe different methods of capacity expansion.

• Recognize the relationship between present and future capacity

requirements.

PIPE SIZE OPTIMIZATION

INTRODUCTION

OBJECTIVES



10


Pipelines are designed not only to meet present needs, but also toaccommodate future demands. In addition, economic factors such as

the high cost of equipment and component parts also affect pipeline

design. The design engineer is faced with the dilemma of satisfying

the capacity requirements for all foreseeable demands while at the

same time minimizing the economic burden of building and

operating the pipeline. Selection of the most desirable combination

of design factors to maximize capacity and minimize cost is called

optimization.

The selection of the size of the pipe is a crucial factor in designing a

pipeline (see Figure 5). The pipe size, wall thickness, and strengthdetermine the operating conditions of the pipeline. The diameter

determines the compression requirement for a given volume.

Figure 5 Pipe Sizing Optimum pipe size satisfies capacity requirements at a reasonable cost. An

oversized pipeline results in overspent funds, while an undersized pipeline

restricts capacity.

The pipe size selection process is not complete without considering

the cost of all the factors. Smaller pipe limits the volume and flow

but costs less. Larger pipe has lower pressure loss and operating

pressures, but costs more. All factors (cost of materials, cost of

operation) must be determined to identify the most effective pipeline

design.

PIPE SIZING &SELECTION

PHYSICAL

PROPERTIESOF THE GAS

ELAPSED TIMEOVER

CAPACITY

Capacity = Volume

Elapsed Time

$

$ LIMITED

CAPACITYVOLUME



11


The selection of pipeline size involves calculating the annual costs ,which are the costs incurred every year in the operation of a pipeline

system. These annual costs are divided into two categories:

• fixed (capital) costs, and

• variable (operating) costs.

Fixed costs are costs which do not depend on the capacity of the

pipeline. An example of a fixed cost is property tax. Variable costs ,

unlike fixed costs, are dependent on the capacity of the pipeline. An

example of a variable cost is the cost of compressor fuel.

Total annual costs are approximately 20% of the capital costs for a

typical pipeline.

A pipeline has reached its capacity when there is no more physical

room to increase the throughput under any conditions. Consequently,

the discharge pressures of the existing compressor stations cannot be

increased nor can suction pressures be decreased. Capacity expansion

is the process of safely increasing the volume capacity of an existing

pipeline. Methods of achieving increased capacity include adding:

• parallel line (“looping”)

• adding more compression at existing stations.

The decisions on what measures to take for increasing pipeline

capacity depend upon the increased volume requirements. If the pipeline capacity needs to be doubled, normally the solution would

be to loop the pipeline completely. For increases between 10% and

50%, the pipeline company has the choice of installing a combination

of loops and additional compression, depending on design

requirements.

ECONOMIC FACTORS

PIPELINECAPACITYEXPANSION



12


Pipeline loops are similar to parallel electric circuits as described inFigure 6. In Figure 6, the flow in both the main and looped lines

between Points A and B depends on the relative size of each line’s

inside diameter. However, the pressure drop in each line is identical,

since the two lines are connected to the same two end points.

Looping is the installation of sections of pipe of different sizes that

run parallel to the existing pipeline to change the capacity of the

pipeline. Looping is usually added to the downstream segment of a

section between two compressor stations to reduce the pressure loss

between stations.

Figure 6 Looped Pipeline

A pipeline loop is similar to an electrical circuit. As the gas flow (current)

reaches Point A, it separates into two streams. The sum of the flows(currents) in each stream is equal to the flow (current) before and after Points

A and B.

The capacity of a pipeline can be increased by installing more

compression at stations along the pipeline. The additional

compression is required to compensate for pressure loss at the higher

flow rates.

The pipeline designer must know the expected capacity of the

proposed pipeline. However, it is often difficult to forecast future

capacity requirements. For example, future capacity requirements

may increase with the addition of more production from newlydrilled wells or newly discovered fields. New customers may be

added to the system, such as gas fired power plants. In contrast,

future capacity may decrease as gas field productivity decreases due

to reservoir depletion.

PIPELINE LOOPS

A B

A B

ADDITIONALCOMPRESSOR

STATIONS

CAPACITYREQUIREMENTS



13


Nevertheless, estimates of pipeline input and delivery volumes arerequired. Often, compromises are made between building a pipeline

capable of handling future requirements and one capable of handling

only current requirements. Economics is the key consideration. If

excessive capacity exists for an extended period of time, the

system’s profitability is reduced. Conversely, if the pipeline’s

capacity is smaller than the volume demand requirements, profits are

not being maximized and the system must be expanded.

Generally, pipelines are either designed with some excess capacity or

so that capacity can be increased with the addition of compression

limited by the Maximum Operating Pressure (MOP) of the system.

MOP is the highest pressure at which a given segment of a pipelinecan be safely operated. MOP is determined by regulations governing

pipe size, weight, material composition, and geographic area in

which the pipeline is located.



14


1. What does pipeline design consider?a) Future capacity demand only

b) Right of way as highest priority

c) Present and future capacity requirements

d) All of these

2. How is the annual cost of operating a pipeline divided ?

a) Into short term and long term costs

b) Into fixed and variable costs

c) Into gross and capital costs

d) Into gross and net costs

3. Which of the following is NOT an option for increasing thecapacity of a pipeline?

a) Looping portions of the pipeline

b) Adding compressor stations

c) Adding compression at existing stations

d) Operating above the MOP

4. What are the key considerations in sizing a pipeline?

a) Economics

b) Gas supply

c) Customer demand

d) All of these

Answers are at the end of this module.

REVIEW 2



15


PIPE WALL THICKNESSCALCULATIONS

SECTION 3

Pipeline regulations set out the standards that must be followed in

designing a pipeline. In the United States, all gas pipelines must be

designed according to the Department of Transportation Regulation,

DOT 49 CFR Part 192 – Transportation of Natural and other Gas by

Pipeline. The international standard for pipeline design isANSI/ASME B31.8 – Standard for Gas Transmission Piping

Systems.

This section of the module describes how the nominal wall thickness

is determined for a design pressure. This calculation is done after the

pipe size has been determined through an optimization process.

The module PIPELINE DESIGN FUNDAMENTALS gives numerical

examples of pipe stress and wall thickness calculations.


objectives.

• Identify the factors involved in selecting the pipe wall thickness.

• Recognize the causes of pipe stress.

• Understand the application of wall thickness/design pressure

formulas.

INTRODUCTION

OBJECTIVES



16


Once the optimum pipe size (diameter) is determined, the wallthickness and design pressure must be calculated in order to

establish the pipe specifications. These calculations are set out in

detail in ANSI/ASME B31.8 – Standard for Gas Transmission Piping

Systems. Some jurisdictions have special or supplementary

requirements that go beyond B31.8

The initial selection of a pipe wall thickness for a specific

application is based on the following factors:

• design pressure

• pipe diameter

• pipe material grade

• class location• pipeline operating temperature

• longitudinal pipe joint factor.

Figure 7 Gas pipeline inNorthern

Canada

Additional factors may influence the final selection of pipe wall

thickness. Factors that may require consideration include:

• foreign crossing requirements

• external forces

• corrosion allowance

• transportation and handling during construction

• other non-typical loadings.

Figure 8 Pipes being transported during construciton

PIPE WALLTHICKNESS

CALCULATIONS

SELECTING PIPE WALLTHICKNESS

CAUSES OF PIPESTRESS



17


The design pressure for gas pipeline steel piping or the nominal wallthickness for a given design pressure is determined by using the

following ASME B31.8 formula:

where: t = nominal wall thickness (in.)

OD = nominal outside diameter of pipe (in.)

P = design pressure (psig)

S = specified minimum yield strength (psi)

F = design factor

E = longitudinal joint factor

T = temperature derating factor

The outside diameter of the pipe (OD) and the design pressure are

determined by the design optimization process. The pipe minimum

yield strength (S) and the longitudinal joint factor (E) are established

from the pipe manufacturer design specifications .

The design factor (F) changes, depending on the final location of the

pipe within the pipeline system. The ANSI/ASME B31.8 code sets

out a procedure for dividing the pipeline into class locations (1, 2, 3

or 4) based on the number of buildings or population in proximity to

the pipeline. There is a different design factor for each class location

and within each class location there may be additional increases in

design safety factors to account for added stress on the pipeline, e.g.

road crossing or compressor station piping.

A temperature derating factor is applied if the pipeline will operate

above 150 °F (65 °C). Natural gas transmission pipelines are

normally limited to a maximum operating temperature of 120 °F

(49 °C). Above this temperature, the external coating will have the

potential to disbond, exposing the pipe and creating the possibility

of corrosion.

The final pipe wall thickness can be determined once all pipeline

design factors are known. Typically, a gas transmission pipeline will

have a thin wall pipe in remote, sparsely populated areas. Heavy wall pipe is installed at road, river and rail crossings, throughout

populated areas, in cities and towns, and at compressor stations.

P =2 × S × F × t × E × T

OD

DESIGNPRESSUREFORMULA



18


1. What is the international standard for pipeline design?a) API 6D

b) ANSI/ASME B31.8

c) ASME Section VIII

d) All of these

2. Which of the following factors is not used to select pipewall thickness?

a) Pipe diameter

b) Class location

c) Gas quality

d) Design pressure

3. What are determined by the design optimization process?

a) Outside diameter (OD) and design pressure (P)

b) Longitudinal joint factor (E) and specified minimum yield

strength (S)

c) Class location and design factor

d) All of these

4. Where is heavier wall pipe usually installed?

a) At road crossings

b) At river crossings

c) At compressor stations

d) All of these

Answers are at the end of this module

REVIEW 3



19


PIPELINE COSTSSECTION 4

This section describes the main components that make up the cost of

a gas pipeline. These costs can be grouped as follows:

• Right-of-way costs

• Material costs

• Construction costs

• Engineering and contingency costs.

For information on compressor station costs, readers should refer to

the module – COMPRESSOR STATIONS.

After this section, you will be able to complete the following objective.

• Identify the major components of transmission pipeline costs.

INTRODUCTION

OBJECTIVES



20


The cost of a gas transmission pipeline is made up of the followingcomponents:

• Right-of-way (ROW) cost

• Material cost

• Construction cost

• Engineering and contingency.

Material and construction costs are the major cost components.

Together, they make up 60% to 70% of the total project cost. A

discussion of each component follows.

Right-of-way costs consist of payment for land rights as well as

compensation for work related damages. These include damages to

crops, trees, and fences.

The key factors affecting ROW costs are:

• Population density

– Higher density means higher costs

Figure 9ROW through high density area

• Environmental sensitivity

– Environmentally sensitive areas can be bypassed but this results

in increased pipe and pipeline costs

Figure 10 ROW through environmentally sensitive terrain.

RIGHT-OF-WAY (ROW)COSTS

COST OF GASTRANSMISSION

PIPELINES



21


• Time urgency – If negotiation time is short, ROW costs may increase

• Surveying requirements

– Surveys for easements across federal and state lands can be more

expensive than private property

Material costs include the pipe, coating, valves, and fittings. These

costs increase significantly as the pipe diameter increases.

The pipe is the most costly item. The wall thickness establishes the

weight of the pipe, which determines the cost.

Factors that affect the cost of materials are:

• Design flow rate and MOP of pipe

– These establish the size of pipe, valves, and fittings

• Population density along ROW

– This establishes the wall thickness of pipe

• Availability of material

– Some sizes and specifications of pipe material may be in short

supply, driving up costs. This will depend on the number

of similar pipeline projects happening concurrently.

In addition to material costs, construction costs are a major component

of total pipeline costs. The key factors that influence construction

costs are:

• Population density

– Urban areas present more obstacles to pipeline construction

than rural areas

• Environmental constraints

– Construction costs will increase with directional drilling,

terrain restoration, and archaeological sites

MATERIAL COSTS

CONSTRUCTIONCOSTS



22


• Rough terrain – Rocky areas, wetlands, and mountainous terrain can increase

construction costs greatly

Figure 11Pipeline construction through mountains

• Weather factors

– Winter construction in cold climates, summer construction in hot

climates, or rainy season construction can increase labour costs

considerably

• Availability of contractors

– If contractors are busy, bid prices will increase.

Engineering costs are dependent on the complexity of the project.

They could be significant if there are several complicated engineering

designs such as water crossings, unstable slope areas, and

mountainous terrain.

Contingency costs are included to cover unknown project costs.

These include material price escalation, unexpected construction

difficulties, ROW acquisition problems, or unusually bad weather.

The more the estimators know about a project, the lower the

contingency cost should be.

ENGINEERING &CONTINGENCY COSTS



23


1. What are the major cost components of a gas pipeline?a) Engineering and contingency

b) Material and construction

c) Right-of-Way and engineering

d) Construction and engineering

2. Population density is a key factor in the cost of a pipeline.

a) True

b) False

3. What are the main factors that affect the cost of pipeline

materials?a) Design flowrate

b) Population density along ROW

c) Availability of materials

d) All of these

4. Which is not a key factor in the construction costs of a pipeline?

a) Population density along ROW

b) Environmental constraints

c) Survey requirements

d) Rough terrain

5. What is the result when the estimators know more about a pipeline project ?

a) It should lower engineering cost

b) It should lower contingency cost

c) It should lower ROW cost

d) It should lower population density

Answers are at the end of this module

REVIEW 4



24


SECTION 1 – PIPELINE DESIGN FUNDAMENTALS• To design a pipeline, it is necessary to understand the pipe

characteristics, physical properties of the gas, and the relationship

between the pipe and the gas.

• The main pipe characteristics in pipeline design are inside

diameter, length, and relative roughness.

• The physical properties of the gas that are considered in pipe

design are viscosity, specific gravity, compressibility, and

temperature.

• The three steps to determining pressure loss due to friction in a

pipeline are: – Calculate the Reynolds Number (Re).

– Determine the Friction Factor (f) from the Moody diagram.

– Calculate the pressure loss using an industry flow formula.

SECTION 2 – PIPE SIZE OPTIMIZATION• Optimization is the selection of the most desirable pipeline design

that maximizes throughput capacity at a minimum cost.

• The annual costs of a pipeline are made up of fixed costs (which

do not depend on capacity) and variable costs (which are capacity

dependent).

• The methods for increasing capacity of a pipeline are looping and

adding more compression at existing stations. Optimization is used

to select the best expansion method.

• Pipeline capacity design is often a compromise between meeting

projected future requirements and meeting current demands.

Generally, pipelines are designed with expansion capability at

reasonably low cost.

SECTION 3 – PIPE WALL THICKNESS CALCULATIONS• The pipe wall thickness is calculated once the optimum pipe

diameter and design pressure (MOP) are determined. These

calculations are done according to formulas set out in governmentregulations, such as DOT 49 CFR Part 192 in the U.S.

SUMMARY



25


• The factors that determine pipe wall thickness are: – design pressure

– pipe diameter

– pipe material grade

– class location

– pipeline operating temperature

– longitudinal pipe joint factor.

• Each pipeline is divided into class location, depending on the

proximity to buildings and population. A design factor is assigned

to each class with increases to account for added stress on the

pipeline due to unusual loads (e.g. road crossings) or external

forces (e.g. unstable slopes).• The final pipe wall thickness is calculated for the different

locations once all the factors are known. Typically, gas pipelines

have thin-walled pipe in remote areas and heavy-walled pipe at

river, road and rail crossings and through populated areas.

SECTION 4 – PIPELINE COSTS• The total cost of a gas pipeline can be broken up into the following

four components: Right-of-way, Material, Construction, and

engineering and contingency. The largest cost areas are material

and construction.

• Right-of-way costs increase with population density, environmentalsensitivity, short negotiation timeframes and increased survey

requirements.

• Material costs are a function of the pipe diameter, pipe wall

thickness, and current availability of pipe.

• Construction costs are driven by ROW population density,

environmental obstacles, rough terrain, weather, and contractor

availability.

• Engineering costs increase with the number of specific unusual

pipeline designs required. Contingency costs decrease as more

detailed information is known about the project.



26

annual coststhe costs incurred every year in the operation of a pipeline system.

(p. 11)

fixed costs

operational costs that do not depend on the capacity of the pipeline.

(p. 11)

laminar flow

a flow in which the gas in the center of the pipe moves faster

than the gas near the pipe walls. (p.6)

looping

the installation of additional sections of different sizes of pipe thatrun in parallel and are connected to the original pipeline to change

the capacity of the pipeline. (p.12)

Maximum Operating Pressure (MOP)

the highest pressure at which a given segment of a pipeline can be

safely operated. (p.13)

Moody Diagram

a graphical representation of friction factors for a series of related

flow conditions, whose curves relate two dimensionless parameters

(the Reynolds Number and the relative roughness of the inside pipe

wall) to the friction factor. (p. 5)

optimization

selection of the most desirable combination of pipeline design factors

to maximize capacity and minimize cost. (p.10)

Reynolds Number

mathematical relationship that defines the interdependence between

the pipe diameter, liquid viscosity, and flow viscosity. (p.5)

steady state

operating condition of a system, such as a pipeline, that stays

constant or does not change over time. (p. 6)

variable costs

costs of pipeline operation that change with increases or decreases in

pipeline operational capacity. (p.11)


GLOSSARY



REVIEW 1 REVIEW 2 REVIEW 3 REVIEW 41. a 1. c 1. b 1. b

2. d 2. b 2. c 2. a

3. a 3. d 3. a 3. d

4. b 4. d 4. d 4. c

5. b

ANSWERS


gas pipe line design

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