Pipe Line equipment

8/11/2019 Pipe Line equipment

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INTRODUCTION TO PIPELINE EQUIPMENT

TABLE OF CONTENTS

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

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

SECTION 1 PIPELINE CONSTRUCTION, MAINTENANCE & REPAIRIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Pipeline Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Pipeline Maintenance & Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Review 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

SECTION 2 NATURAL GAS STORAGE

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Gas Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Liquefied Natural Gas (LNG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Review 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

SECTION 3 COMPRESSOR & MOTOR OPERATIONSIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Compression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Selection Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Motor Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Review 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

SECTION 4 CUSTODY TRANSFER MEASUREMENT, CONTROL SYSTEMS

& INSTRUMENTATION

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Custody Transfer Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Control Systems & Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Review 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

SECTION 5 VALVESIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Basic Valve Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46Isolation & Block Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Special Purpose Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Review 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

SECTION 6 VARIABLE SPEED DRIVESIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Variable Frequence Drives (VFDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Review 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

SECTION 7 INDUSTRIAL ELECTRICITY & ELECTRICAL POWER

MANAGEMENTIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Fundamentals of Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Industrial Electrical Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Electrical Power Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Review 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

ANSWERS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80


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PLEASE NOTEOperations personnel use a combination of skill, knowledge, andtechnology to accomplish specific goals. A key objective of the Gas

Controller Training Program is to promote an understanding of the

oretical 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.


GAS CONTROLLER TRAINING PROGRAM

2002 ENBRIDGE TECHNOLOGY INC.

Reproduction Prohibited

ENBRIDGE TECHNOLOGY INC.

Suite 601, PO Box 398

10201 Jasper Avenue

Edmonton, Alberta

Canada T5J 2J9

Telephone +1 - 780-412-6469

Fax +1 - 780-412-6460

Reference: G-0.3 Introduction to PL Equipment OCT 2002


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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.


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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, ifthere is a topic or a definition that you do not recognize, you can

easily find it in the module.


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Pipeline Controllers are responsible for safe and efficient

transportation of natural gas through thousands of kilometers of pipe.

Controllers use a computer-based control system to manipulate

equipment they do not see first hand. Controllers require detailed

knowledge of the physical characteristics of the pipeline and the

pipeline equipment to make effective decisions; they spend a large

portion of their time communicating with mechanics, electricians, and

other field maintenance staff, discussing equipment that affects

pipeline operations.

This module is an overview of modules detailing applications of

pipeline equipment in the Gas Controller Training Program, Phase 2

Pipeline Equipment. This module discusses the key concepts related to

applications of pipeline equipment and serves as an introduction and

study guide to Phase 2 Pipeline Equipment.

Because this module is general in nature: the specific details of many

components, processes, and procedures are not fully explained.

References to specific modules are provided in order to enable the

reader to retrieve more detailed information from individual modules.

This module provides information on the following goals.

It describes the elements and stages of development of the pipeline

system, the major components, and its construction.

It illustrates how pipeline equipment operates.

None

1


MODULE GOALS

INTRODUCTION

PREREQUISITES


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The construction of pipelines is a complex operation: careful

planning and economic analyses are conducted before construction

begins. Once construction starts, equipment, materials and personnel

are mobilized. Pipelines are then built, repaired, and maintained in

the most environmentally friendly way possible.

.

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

objectives.

Identify the major steps in the construction of a pipeline from the

design phase to commissioning.

Identify the spread of personnel and equipment and mobilization

of the spread.

Recognize the types of inspection that occur on pipelines.

Examine the main elements of a preventive maintenance program.

Identify some methods of isolating pipeline sections.

PIPELINE CONSTRUCTION,MAINTENANCE & REPAIR

INTRODUCTION

OBJECTIVES

SECTION 1


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Economic, environmental, health, and safety factors must beconsidered in determining the appropriate transportation method for

a particular product. Pipelines are generally the method of choice for

economical transportation of natural gas. By way of comparison, for

every dollar it takes to ship by other methods - rail, truck or tanker -

it may cost as little as ten cents to ship by pipeline. In addition,

through careful planning, pipelines can be built so that

environmental concerns are minimized both during the construction

phase and afterwards.

Before construction can begin, careful analyses of all aspects of the

proposed project must be conducted and a detailed project plan

drafted. The module - PIPELINE CONSTRUCTION describes the variousstages of pipeline construction, including:

planning and design

construction preparation

the mobilization of personnel, equipment, and materials

construction, and

special construction issues.

The company sets up a project management team to oversee the

entire construction project and a pipeline route is selected that avoids

problem or sensitive areas. In order for construction to begin, govern-

ment agencies must approve the pipeline route. Some agencies thathave a major impact on the regulation of pipeline systems in Canada

are provincial departments and boards and the Ministry of the

Environment. In the U.S., state departments and the federal

Environmental Protection Agency regulate pipeline construction.

Other organizations, like utility boards, may also have concerns that

must be addressed before construction can begin.

The construction company must consider both environmental and

cultural concerns: the preservation of significant environmental areas

and cultural or archaeological sites in the path of the pipeline is

considered during the planning and design phases of construction.

Soil analyses are conducted to ensure the pipeline is adequately

supported by the soil. Finally, land must be procured, and legally

surveyed by ground or by the use of aerial and satellite photographs.

After surveying is complete, the planning team negotiates with the

various landowners to obtain the necessary right of way (ROW).

PIPELINECONSTRUCTION

PROJECT PLANNING &DESIGN


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Construction preparation requires the efficient use of personnel,equipment, and materials. Personnel can be divided into administra-

tive and trades people, all of whom play a key role in ensuring that

the construction project proceeds smoothly. The equipment used on

the pipeline is extensive, and includes bulldozers, pipe layers, taping,

automatic production welding machines, graders, ditching machines,

and tractors. In addition, many different types of materials are used

on construction sites, including pipes, lubricating oils, welding

materials, clamps and testing equipment. All material must meet rigid

quality control standards.

The pipeline construction project is called a spread. The spread is thecrew and the equipment required to build a pipeline from an intact

ROW to the commissioning stage of the pipeline. The size of the

spread is influenced by the construction schedule, the terrain, and

special construction situations like water crossings. Large projects can

mean a spread of over 100 different pieces of heavy equipment and

over 500 workers strung out for miles along the pipeline ROW route.

The spread may handle every facet of construction, or subcontractors

may be awarded some of the work. In essence, the spread is similar to

a complex moving assembly line.

Mobilization of personnel, equipment, and materials is extremely

important: access routes must be acquired or built, and equipmentmust be properly maintained. In addition, all materials must be

available as required. Environmental concerns must also be met in

accordance with government regulations and the company's own code

of practice. Topsoil removed during the ditching process must be left

undisturbed in piles along the ROW until it can be replaced, and

access routes may have to be returned to their original condition.

5


CONSTRUCTIONPREPARATIONS

MOBILIZATION


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The first step in constructing a pipeline is clearing and grading theROW so work crews and heavy equipment can reach the site.

The next step in pipeline construction is ditching. Ditching is the

digging of a ditch wide and deep enough to contain the pipeline.

Figure 1Ditching Operation

Pipe stringing is the next step after the ditch is excavated. During

stringing, lengths of pipe are transported to the construction site andlaid out end-to-end on the grade beside the ditch.

Figure 2Stringing the Pipe

CONSTRUCTION


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Certain pipe sections need to be bent to fit the contour of the ditch. Ahydraulic bending machine bends the individual pipe segments in

order to accommodate changes in direction and elevation of the land

where required.

The welding crew follows the bending crew, welding the pipe lengths

into a continuous section of pipeline.

Figure 3Welding a Root Bead

A welder is performing a root bead pass on a pipeline on a lake crossing. Note

the external clamp.

Welding inspectors inspect the weld to ensure weld integrity, usingradiographic testing. This method of testing weld integrity takes an

x-ray of the weld. Any defect welds must be repaired before the

pipeline is commissioned.

Figure 4A Special Radiographic Machine


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The welded joint is cleaned and coated after the weld is completedand tested.

Following coating, a series of side boom tractors carefully lower the

pipe into the ditch.

Figure 5A Side Boom TractorAs the most common way of

lifting and moving heavy pipe

short distances, these tractors

suspend the pipe from the boomand use a counter-weight

opposite the boom to keep from

tipping over.

The pipe sections are hydrostatically tested to ensure pipeline

integrity before back filling. Hydrostatic testing involves injecting

water into the sealed pipe and pressurizing to 125% of the maximum

operation pressure (MOP) of the pipe to ensure pipe and weld

integrity. The ditch is backfilled after the testing using the soil origi-

nally removed during the ditch procedure.

Once all of the pipeline sections have been welded and hydrostatic

testing completed, welding crews begin to tie in the sections.

Essentially, tying in means making the final welds, joining all pipe

sections together to form a continuous pipeline from the starting point

to the end point.


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Figure 6Tying InA tie-in crew works on a section of

pipe inside a portable shoring

cage, which provides then

protection inside the ditch.

The pipeline is ready for

commissioning upon comple-

tion of the final tie-ins.

Commissioning involves final

inspection by engineering and

technicians, dewatering pipe

sections, purging and loadingthe line with gas, and opening

mainline section valves to

begin flowing the gas.

When pipelines cross roadways, special care is taken to ensure both

pipeline integrity and also to avoid damage to the roadbed. First,

crews bore a hole under the road. Then, either a casing support or a

thick walled pipe is installed in the bore and pulled to the other side.

If a casing is used, the carrier pipe is installed through the casing and

pulled through the other side. Once the pipe is installed, crews weldthe pipe to the rest of the pipeline.

There are four methods of crossing waterways:

In an aerial crossing, the pipeline is suspended across the waterway.

Using the conventional ditching method, the pipe is floated across

the waterway, then sunk into a ditch excavated in the bed of the

waterway.

Crews drill under the waterway using computer controlled direc-

tional drilling equipment.

Lay barges are used to lay pipeline across very large waterways. Laybarges are extremely large barges that fabricate pipe, test it, and then

release it in the desired position.

SPECIALCONSTRUCTIONISSUES

WATERWAY CROSSINGS


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Existing pipelines and utilities are hand excavated to confirm theirlocation. This ensures that these pipelines and utilities are identified,

located, and protected. In addition, before excavation, utilities and

foreign pipeline owners are notified. No mechanical excavation is

allowed to occur within 5 ft (1.5 m) of an existing pipeline.

Special types of terrain require specialized construction techniques.

In Canada, swamps are crossed during winter to allow the use of

heavy equipment. The pipeline is kept in place by heavy concrete

weights known as saddle weights.

Tundra is another difficult terrain area. Constructing pipelines on the

tundra requires great care in order to protect the ecologically sensitive

landscape. In tundra areas, workers elevate and insulate the pipeline

to prevent melting the permafrost.

Hilly terrain also requires specialized construction techniques and

additional equipment that must be secured in place by cables.

Backhoes can be used for precise work in rocky soils that are

commonly encountered in hilly terrain. The right of way is cleared by

blasting away the rock, or by the use of backhoes or bulldozers

equipped with rippers.

In urban areas, the pipeline right of way is fenced in order to ensure

public safety. Great care is taken when excavating in order to avoidhitting buried cables or lines.

Environmental concerns are paramount in any pipeline construction

project. Waterways must be crossed without disturbing habitat,

wildlife, or fish populations. During construction in hilly terrain,

drainage ditches are built, so the pipeline route does not become a

waterway. In addition, construction camp waste must be properly

cleaned up before the construction project is complete.

PIPELINE & UTILITIES

TERRAIN

ENVIRONMENTAL & PUBLICPROTECTION


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Most pipeline companies have a complex maintenance and repairsystem. Good maintenance practices allow companies to detect small

problems before they become large and costly. Although Controllers

are not directly responsible for maintenance or repair, they must be

able to communicate with maintenance personnel in order to ensure a

smooth running operation of the pipeline.

The module - PIPELINE MAINTENANCE describes the basic techniques

and methods of maintenance and repair and the impact these

activities have on line operation. The importance of proper

inspection of the pipeline cannot be over-emphasized. The lack of a

preventive maintenance and repair program can have severe

consequences ranging from environmental disasters to loss of life.PIPELINE MAINTENANCE describes and discusses:

the elements of a preventive inspection and maintenance program,

and

the industry procedure used for repairing pipelines.

The following types of inspections are carried out on most pipelines:

Flyover inspections use aircraft to check large sections of the

pipeline for major signs of trouble, such as gas leaks and withered

vegetation around the pipeline route (indicating a leak).

Linewalking inspections consist of company personnel patrolling

the pipeline route and checking for any problems. Hydrostatic testing is done to test the integrity of a new pipe, or an

old pipe that may have to operate under higher pressure.

Electronic inspection tools are used to check the inner surfaces of a

pipeline for corrosion, pitting, or other damage and wear and tear.

Preventive maintenance is done to forestall high repair bills and

increase efficiency in pipeline operations. Preventive maintenance

consists of corrosion control, equipment inspection, equipment tune-

ups, and instrument calibration.

Corrosion is the natural deterioration of a substance as a result of the

environment. Pipeline corrosion can be both internal and external.

Internal corrosion is caused by moisture in the gas deposition on the

pipe walls and is controlled by the use of cathodic protection and by

the injection of chemical inhibitors into the pipeline.

PIPELINEMAINTENANCE &REPAIR

MAIN LINE

PREVENTATIVEMAINTENANCE

CORROSION CONTROL


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External corrosion is caused by the difference in electrical potentialbetween the soil and the pipe and/or oxidation caused by water and

minerals in the soil. To protect the pipeline from external corrosion,

the pipeline is coated. In coating, a corrosion inhibiting film is

applied to the pipeline. In addition, a cathodic protection system is

installed. In cathodic protection, an electrical current is created

around the pipeline to reverse the flow of electrons to inhibit external

corrosion.

Figure 7Factory Applied Coating

Another type of external corrosion can occur because of a stray

current from an existing cathodically protected pipeline, or by sourceof direct current, such as railroads or powerlines. This type of

corrosion can be controlled by changing the environment around the

pipeline.

Figure 8An Illustration of Stray Current Interference from an ElectrifiedRailway and Power Lines

Anodic Area

Partial Current Return Cathodic Area

Electric Sub-Station

Current Path


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Pipeline equipment is inspected regularly to prevent unnecessarystress on equipment, loss of throughput, and unnecessary callouts.

Equipment tune-ups and instrument calibration are an integral part of

equipment maintenance routines. For example, valves and meters

require regular calibration to prevent problems like false alarms or

incorrect readings.

Monthly checks are conducted to ensure that the pipeline control

system is communicating properly with the field equipment. If there

is a breakdown in communications, the field equipment must respond

to ensure safe operating conditions.

Electronic inspection tools are an important part of internal pipeline

maintenance. Inspection requires a great deal of planning and

communication between maintenance and operating personnel, and a

thorough study of the line to be inspected must be done before the

tool run commences.

There are a number of different types of tools, each with its own

particular function. Cleaning tools also known as pigs, clean the inside

of the pipeline to prevent build-up of deposits that could slow down

gas flow rates.Smart tools are equipped with data collection devices

that collect and store information as the tool travels down the line .

Figures 9 and 10 illustrate scraper and smart tools respectively.

Figure 9Two Types of ScraperPigsA is an example of a

tool with urethane blades

(scrapers) that are better

at removing deposits. B

shows a tool with wear-

compensating brushes,

commonly used in new

pipe to remove scale or

hard deposits.

EQUIPMENT INSPECTION &TUNE-UP

PIGGING

Flow

Scrapers

Flow

Brushes


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Figure 10Typical Caliper Tool Used to Survey Pipeline Geometry

This type of tool detects dents and buckles, which might indicate sagging.

Sonar tools (Figure 11) are used to detect the effects of shifting and

settling that can affect the curvature of the pipeline.

Figure 11A Typical Curvature Tool

Magnetic flux or ultrasonic tools detect corrosion, gouging, or metal

loss in pipelines. Figure 12 is an illustration of a magnetic flux tool.

Figure 12Conventional Magnetic Flux Tool

Flow

Tracker Recorder Sonar & Internal Battery Pack System

Flow

Instrument Magnetic Sensing Drive Section Section Section


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Older pipelines often need to be repaired. Therefore, techniques havebeen devised to perform basic repairs without significantly affecting

throughput. The main steps in repairing a pipeline are:

isolation

pumping down and blowing down the gas

purging the line of gas with air movers

repair/replacement, and

testing and startup.

Before commencing any pipeline repairs, the section of the pipeline

to be repaired must be isolated from throughput and also from any

explosive vapours.

On a gas line, the mainline valves upstream and downstream of the

repair location are closed. In some cases, valves for two sections

upstream and downstream are closed if there is potential for a leak at

either of the valves. The section of line is compressed down to atmo-

spheric pressure into another line, to conserve gas. The remainder of

the gas is blown down to atmosphere.

A hot cut is made on the pipe to create an opening to draw air into

the line so the gas can be purged out using air movers. The air

movers are mounted at each section valve and draw air from the

opening toward the valves and exhaust any gas to the atmosphere.

The air movers continue to operate throughout the job to ensure a

gas-free work area.

If a damaged section of line must be replaced, it is cut out and

removed, and a new piece of pipe is then welded in its place.

Sometimes, however, a technique called sleeving is utilized, that

allows for repair without removal of a full section of pipe. Figure 13

illustrates a typical sleeve used for repairing pipeline segments.

Figure 13A Typical Welded Sleeve Used for Repairing Defects

REPAIR OVERVIEW

ISOLATING THE GASPIPELINES

REPAIR ORREPLACEMENT


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Testing of repaired pipe sections is essential to ensure structuralintegrity. Testing methods include the use of radiographic or x-rays,

ultrasonic testing, or hydrostatic testing. The pipeline can be started

up again if no problems are found during the testing.

TESTING &START UP


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Figure 14

Pipeline Construction Sequence


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1. After the pipe has been strung along the route, the nextstep is ________.

a) wrapping

b) welding

c) lowering

d) bending

2. Lay barges are used when pipelines must cross ________.

a) small bodies of water like streams

b) tundra

c) large bodies of water like lakes

d) swamps

3. Which of the following are not used to protect pipelinesfrom corrosion?

a) mud plugs

b) coating

c) cathodic protection

d) injection of chemical inhibitors

4. Magnetic flux tools are used to detect ________.

a) corrosion

b) the effects of shifting and settling that can affect the curvatureof the pipe

c) metal loss

d) both a and c

5. Isolation of lines can be achieved through the use ofsection valves.

a) true

b) false

Answers are at the end of this module.

REVIEW 1


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Gas is stored in large underground caverns, in rock and salt

reservoirs, or in depleted underground oil and gas reservoirs. Gas can

also be stored as a liquid (LNG) in tanks after it has been cooled to

the point that it turns into a liquid state. This is a very expensive

process and is not done unless it is cost effective for the application.

The transmission pipeline is also used for storage, which gas is

compressed to a higher pressure, resulting in more being stored in the

same volume of pipe. This concept is known as line pack.

The storage of natural gas allows the utility company to quickly

respond to unexpected shortage and peak demands, to guarantee

energy requirements, and to control costs.


objectives.

Recognize the different type of natural gas storage options.

Recognize the reasons why natural gas is liquefied.

Recognize the necessity of insulating LNG storage tanks.

Recognize the design requirement for evapourizers located near

LNG storage tanks.

Understand the advantages and disadvantages of natural gas storage

in gaseous and liquid state.

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NATURAL GAS STORAGESECTION 2

INTRODUCTION

OBJECTIVES


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Natural gas can be stored in gaseous or liquid state. In its gaseousform natural gas is often stored in large underground caverns.

As gases have much lower specific gravities than liquids, storage

volumes for gases are very large, and require huge and expensive

storage tanks. When gas is compressed, storage volumes become

smaller for the same amount of gas.

The transmission pipelines themselves can be used as storage. As the

gas pressure rises inside the pipeline, the volume increases, resulting

in more gas being stored in the pipeline.

When natural gas demand is high, gas is withdrawn from the

reservoir into the pipeline system. When natural gas demand is low,natural gas is fed from the pipeline into storage. It is important to

always leave some gas in storage to allow enough pressure to

retrieve the gas when necessary.

Alternatively, natural gas can be liquefied and stored in tanks in its

liquid form.

Natural gas is often stored underground in caverns, in rock, sand or

salt reservoirs, or in depleted underground oil and gas reservoirs.

Caverns must be self-sealing underground reservoirs that are suitable

to safely store very large amounts of natural gas. The gas is injected

into the wells under pressure, this same pressure is used to push gas

out when needed. The caverns must be deep enough to allow for safe

pressurization and must be free of water.

Compressor stations are located in the vicinity of gas storage caverns to

ensure sufficient compression is available to withdraw gas from cavern.

Liquefied natural gas (LNG) is achieved by cooling the natural gas

below its boiling point. LNG is more dense than the gaseous state.

This means that more energy can be stored in the same space, once

the gas is liquefied.

When natural gas is liquefied at -260 F its volume is reduced toabout 1/600 of its gaseous volume.


GAS STORAGE

LIQUEFIEDNATURAL GAS

(LNG)

CAVERNS


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In order to take advantage of this physical property, natural gas isoften liquefied in natural gas liquefaction units. The natural gas in

liquefied state is called Liquefied Natural Gas or LNG.

Natural gas liquefaction plants normally include a complete gas

purification plant, compressor station, storage tanks, and evaporation

plant. The evaporation plant receives LNG from the storage tanks and

evaporates the LNG before it is fed into distribution systems.

LNG storage is also located at terminals and loaded or unloaded from

tankers and at locations wherever liquid needs to be stored to meet

peak demands. LNG can be stored in underground and aboveground

storage tanks.

Aboveground storage tanks are normally double-walled low-

temperature steel tanks, with insulation between the inner and outer

walls. The shape of the tanks can be cylindrical or spherical.

Underground storage tanks are made of well insulated concrete and

used to store volumes of one million cubic feet or more.

The insulation of LNG tanks is a critical design feature. The lower the

temperature at which LNG is stored the more important the quality of

insulation becomes.

When the stored LNG is is needed for consumers, it is fed through a

vaporizers unit to return it to a gaseous state for consumer use. This

process is very expensive and is only used when it is cost effective or

the only storage alternative in a given area.

All storage tanks are equipped with safety devices such as pressure

relief valves, inlet and outlet piping, re-circulation piping, vent

piping, and instrumentation to monitor pressure, temperature, and

storage level.

Advantages of LNG storage are:

large volume can be stored in underground caverns with minimum

maintenance and operating costs

facilities can be built where needed, such as at shipping terminals.

21



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22

Disadvantages of underground LNG storage include: difficulty in monitoring gas losses

difficulty in controlling quality

possible unsuitability or unsafe location in relation to the

surroundings.

Disadvantages of above ground LNG storages are:

the increased cost of additional safety features required to maintain

the process equipment (liquefaction plant, evaporation plant)

higher quality and more expensive construction materials are

needed to operate this type of storage facility.



27/84

1. Why is natural gas stored?a) To increase the sales cost

b) To be able to meet peak demands

c) To meet environmental requirements

d) For quality control

2. Why is natural gas liquefied?

a) To avoid a gas explosion

b) To be able to use existing compressors

c) To store more energy in the same volume

d) All of the above

3. What is between the double walls of aboveground LNGstorage tanks

a) insulation material

b) air

c) natural gas

Answers are at the end of the module.

23


REVIEW 2


28/84


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25


Motors and compressors are key components of a pipeline system

because, in combination, they provide the energy to move the gas in

a pipeline. Proper compressor operation is necessary to maintain

adequate line pressure in order to prevent cavitation and line

separation problems that damage equipment and valves.

Compressors and motors are complex and costly equipment. Damage

to compressors and motors through improper operation can have

serious financial consequences for pipeline operations.

There are many different kinds of compressors and motors used in

the gas pipeline industry. Some compressors use reciprocating

engines, electric motors and others are gas turbines. This section also

discusses the role of controllers in the safe, efficient operation of

compressors and motors.

Compressors deliver gas through the pipeline system from a source

to the end user via several stations and over various distances. The

difference is that gases are compressible, and liquids are not

compressible.


objectives.

Recognize the difference between centrifugal and reciprocating

compressors.

Identify the principal components of a reciprocating compressor.

Identify the principal components of a centrifugal compressor.

List advantages and disadvantages of each compressor type.

Understand the design criteria for compressor selection.

Identify major operational considerations with respect to

compressors.

Identify the principle components of an electric motor.

Identify the principle components of a turbine motor.

COMPRESSOR & MOTOROPERATIONS

SECTION 3

OBJECTIVES

INTRODUCTION


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Compressors deliver gas through pipeline systems from a source tothe end user via several stations and various distances.

Compressors deliver gas, while pumps deliver liquids. The difference

is that gases are compressible, and liquids are not.

The most widely used type of compressors are reciprocating and

centrifugal.

Reciprocating compressors normally operate at slower speeds, and

higher pressures. Many reciprocating compressor units used for

natural gas services contain the compressor and its driver in one unit

called an integral unit.

Large compressors consist of multiple compressor cylinders, which

are mounted on the same crankshaft as the engine cylinders. When

the engine rotates the crankshaft, it also moves the rods connected to

the compressor pistons. In most integral units the engine cylinders

are in vertical or V configuration, while the compressor cylinders are

horizontal.

The cylinders of an integral compressor units can be operated in

parallel or is series. When operated in parallel, each cylinder

compresses a portion of the gas volume and operates with the same

suction and discharge pressure. Integral units can also be operated

with the cylinders connected in series. In this configuration, eachcylinder handles the total volume of gas, and the discharge pressure

of one cylinder becomes the suction pressure of the following

cylinder.

As the size of the cylinders becomes smaller, the discharge pressure

increases. Other components of reciprocating compressors are

suction and discharge valves. Smaller reciprocating compressors that

have separate drivers are often used for auxiliary services.

Reciprocating compressors require regular maintenance due to a high

wear factor and must be always be properly lubricated and cooled to

avoid damage to cylinders and pistons.

Vibration dampers are installed on the reciprocating compressor

discharge piping to minimize the vibration caused by the pulsating

action of the cylinder movements.

COMPRESSORS

RECIPROCATINGCOMPRESSOR


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Centrifugal compressors add energy to the gas by the rotation of theimpeller. A centrifugal compressor discharges gas at high velocity

into a diffuser, where the velocity is reduced and the kinetic energy

of the gas is converted to pressure energy.

Centrifugal compressors consist of a casing, one or more impellers

mounted on a shaft, bearings, and seals. Centrifugal compressors

have a fewer rotating parts than reciprocating compressors, which

reduces maintenance cost and lubricant consumptions.

The gas discharge from centrifugal compressors is smooth and not

pulsating, as from reciprocating compressors. This difference makes

them the preferred choice for offshore applications, because of

minimized vibrations.

Centrifugal compressors cannot provide the same discharge pressures

as reciprocating compressors, unless arranged in series. The capacity

of a centrifugal compressor depends on the size and speed of its

impeller and the discharge pressure. The capacity is directly

proportional to the speed.

The key process parameter for the selection of a compressor is the

ratio between inlet pressure and discharge pressure and the quality of

the gas it must handle. If the pressure ratio is high, several

compression stages must be used. The more a gas is compressed, thehigher its temperature. The temperature limits the allowable pressure

increase in each stage.

Intercoolers are installed in order to limit the gas temperature

between stages. Interstage cooling can be done by air cooling, by

indirect cooling with water, or by gas-to-gas heat exchange. Coolers

are normally installed to dissipate heat developed in the last

compression stage.

Gas separators or mist eliminators are installed between compression

stages and also after the last compression stage to remove

condensates if the gas is wet or contains liquid condensates. Liquidcondensates cause corrosion of compressors, instrumentation and

piping, and contribute to poor gas quality. The quality of the gas also

determines the quality of construction materials required for

transmission system equipment.

CENTRIFUGALCOMPRESSORS

SELECTIONCRITERIA


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Since natural gas is highly flammable, the safety features ofcompressors must include explosion-proof drivers, instrumentation,

and switches.

The critical criteria for a compressor selection at a given installation

is the desirable combination of capital cost, annual operating and

maintenance costs, fuel efficiency, and specific advantages of each

alternative.

Today's gas pipelines primarily use gas turbines as the main driver for

compressor units. These can be derivatives or industrial units. These

units come in 10,000 to 35,000 horsepower ratings, and utilize natural

gas for fuel. In some cases, the turbine will be connected to a booster

for increased power. Turbines are normally connected to

centrifugal compressors.

The termgas turbine refers to a gas-turbine engine, or an internal

combustion engine that employs a continuous combustion process and

converts the energy of a fuel into a form of useful power. A simple

gas turbine typically consists of a compressor, a combustor, and a

turbine. More complex systems result from adding different inlet and

exit components to this generator.

In this engine, the turbine and the compressor are on the same shaft.

The compressor raises the pressure of atmospheric air and sends this

air to the combustion chamber. Here, the natural gas fuel burns,raising the temperature and increasing the heat energy. The hot gas in

the turbine expands to develop mechanical energy, as expanding

steam does in a steam turbine.

A rotating compressor draws in air from the atmosphere, pressurizes

it, and forces it into the combustor (the furnace) in a steady flow. Fuel

forced into the air burns, raising the temperature of the mixture of air

and combustion products. This high energy mixture then flows

through the turbine, dropping in pressure and temperature as it does

work on the moving blades. The spent gases then leave at atmo-

spheric pressure but at high temperature. The turbine drives the

compressor rotor through a shaft and also an external load through the

load coupling. The turbine can be connected to the gas compressor

directly or indirectly.

MOTOROPERATION

GAS TURBINE


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29


Boosters are sometimes installed between the gas turbine and the gascompressor. A booster machine compresses air or gas from a pressure

above atmospheric to a still higher pressure. Booster machines have

many uses in gas pipeline operations. Compression may be either

single or multistage, depending upon the ratio of compressions,

horsepower, and gas analysis.

Figure 15Gas Turbine

The main advantages of the gas turbine engine are:

It is capable of producing large amounts of useful power for a rela-

tively small size and weight.

Since motion of all its major components involves pure rotation

(i.e. no reciprocating motion as in a piston engine), its mechanicallife is long and the corresponding maintenance cost is relatively

low.

Although the gas turbine must be started by some external means

(a small external motor or other source, such as another gas

turbine), it can be brought up to full-load (peak output) conditions

in minutes.

A wide variety of fuels can be utilized. Natural gas is used in

pipeline gas turbines while light distillate (kerosene-like) oils power

aircraft gas turbines.

The gas turbine requires no coolant (i.e. water).

Electric motors use the forces of attraction and repulsion that occur

between two magnetic fields to rotate a shaft connected to the

compressor. The rotating shaft provides mechanical energy that the

PRINCIPLE ADVANTAGESOF THE GAS TURBINE


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30


compressor converts into the required pressure that moves gas in apipeline. In order to understand how an electric motor works, it is

useful to be familiar with magnetic fields and what happens when

they interact.

The term induction refers to the generation of an electric current by

passing a conductor through a magnetic field. When a conductor (for

example, a copper wire) is moved through a magnetic field, the

magnetic field exerts an electromagnetic force upon the electrons in

the wire. The electromotive force that induces electric current in a

conductor passing through a magnetic field always acts perpendicular

to the lines of magnetic force through which the conductor passes,

and perpendicular to the motion of the conductor.

The principle components of an electric motor are the stator and the

rotor.

A statoris a cylindrical set of windings that produces an electromag-

netic field. The major parts of a stator are:

stator frame

stator core

stator windings, and

end shields.

The stator is cylindrical, allowing a rotor to be placed inside it.

A rotor is a set of windings or conductor bars around a shaft which

can rotate freely inside the stator. The major components of a rotor,

which are:

rotor case

rotor windings

rotor end rings, and

rotor shaft.

Figure 22An Electric Motor

An electric motor consists of a rotor placed inside a stator and supported bybearings.

ELECTRIC MOTORS


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31


Stator CoreStatorLaminated Steel

RotorStator

Windings External Fan

Cast Iron FrameEnd Shield

Shaft

Bearings

Enclosure


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32

1. The term induction refers to the generation of __________.a) an electromagnetic field using the chemical reaction inside a

dry cell

b) the generation of an electromagnetic field by current moving

through the conductor

c) the generation of an electric current by passing a conductor

through a magnetic field

d) the generation of mechanical energy using electrical energy

2. The cylindrical set of windings in a motor that produces arotating electromagnetic field is the __________.

a) stator b) rotor

c) end shield

d) shaft

3. The difference between a centrifugal and reciprocatingcompressor is ________.

a) the number of pistons

b) the number of impellers

c) the method of creating pressure

d) the type of driver

4. An intercooler is a _________.

a) special compressor

b) a liquid/gas separator

c) cooler that cools the exhaust gas

d) cooler between compressor stages

5. The pressure ratio is ________.

a) ratio of outlet pressure to inlet pressure

b) ratio of inlet pressure to outlet pressure

c) none of the above

d) all of the above



REVIEW 3


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33


In the pipeline context, custody refers to the ownership of and

responsibility for the gas. Since custody of a product can change

many times between initial production and delivery, the accurate

measurement of the of the transfer points essential.

The module CONTROL SYSTEMS & INSTRUMENTATION, describes the

control of the custody transfer and measurement process by SCADAsystem. This module assists the Controllers to better understand the

importance of the custody transfer and measurement procedure and

the control systems that regulate it.

This section describes the instruments used to measure and control

the safety features at the station.


objectives.

Recognize the importance of custody transfer. Identify methods to accurately measure volumes in pipelines and

storage.

Recognize the importance of quality measurements.

Identify the elements of a control system.

Identify the various instruments that are used to control pipeline

equipment.

CUSTODY TRANSFER MEASUREMENT,CONTROL SYSTEMS & INSTRUMENTATION

SECTION 4

INTRODUCTION

OBJECTIVES


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34

Custody transferis the passing of responsibility during storage andtransportation for a determined or measured volume of gas. Any

losses or gains resulting from inaccurate measurement are the respon-

sibility of the pipeline company.

Some points of custody transfer include:

injection of natural gas into a pipeline and receipt of the gas at a

consumer point or local distribution company.

injection of natural gas into a pipeline and receipt of the gas at a

storage facility, and

movement of natural gas in a pipeline across a jurisdictional

boundary.

Pipeline companies must keep an accurate account of the gas

volumes they handle. The amount of money that pipeline companies

are paid and the amount they pay to producers, royalty owners, and

the government is dependent on the volume of gas that passes

through their facilities.

Volume is not the only important variable. The quality of natural gas

depends on its heat (energy) content. Energy content is expressed in

BTU/scf. The higher the heat content, the higher the value of the

gas.

The payment a pipeline company receives for the gas it handles

depends on the quality of the gas as well as the quantity: Gas qualityis monitored at various stages to ensure the quality remains

consistent from the processing facility to the consumer.

Volume is affected by density, vapour pressure, temperature, and

pressure. These factors must also be measured and the volume

adjusted accordingly. The net standard volume is the meter measured

volume of gas adjusted to standard temperature of 60F (15C) and

standard pressure of 14.7 psi (101.3 kPa). These volume measurements

remain constant, regardless of temperature or pressure changes.


CUSTODYTRANSFER

MEASUREMENT

NET STANDARDVOLUME


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35


Natural gas measurement is necessary because buyer and seller wantto ensure that exact volumes are transferred, and proper payments

made.

Metering is the process used to measure the product flowing past a

particular point in the pipeline. In the pipeline business gas volumes

are measured in thousands of cubic feet (Mcf3) or cubic meters (m3).The measured actual volume is converted to standard volume at

standard pressure [14.7 psi (101.3 kPa)] and standard temperature

[60 F (15 C)].

The flow of natural gas is constantly measured and monitored with

orifice plates, turbine meters, or positive displacement meters.

In order to establish accurate gas volumes, the volume measurements

must be corrected by the temperature factor. Therefore, the

temperature is continuously measured with sensors in the pipeline.

As described later in this section, pressure instrumentation is

installed in various locations of the pipeline and on equipment to

continuously monitor the pressure of the natural gas. Pressure

measurements at transfer points are used to convert actual gas

volumes to standard volumes.

For the custody transfer of natural gas, the heat or energy content is

essential. Therefore, periodic sampling, gas chromatography, andacoustic measurements are used to determine the heat content in

BTU.

FLOW DATA

TEMPERATURE DATA

PRESSURE DATA

ENERGY DATA

CUSTODY TRANSFERMEASUREMENT PIPELINES


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Turbine metersmeasure volume

indirectly by

measuring flow speed

and converting that to

volume. Turbine

meters are suited for

measuring natural gas

and natural gas liquids

(NGL).

Figure 16Turbine Meter

Positive displacement

(PD) meters, measure

volume directly by

capturing and

releasing fixed

quantities of gas from

the stream and

counting cycles in a

run.

Figure 17Positive DisplacementMeter

To ensure accuracy, meters are proved (tested) regularly. Meter

factors and the factor for the effect of temperature on steel must be

applied to arrive at accurate metered volumes. Gas temperature and

pressure must be measured when gas is metered because these

factors affect volume. Correction factors for pressure and

temperature must be applied to convert the metered volume to net

standard volume. Other factors that affect meter accuracy are wear,

build-up of deposits, and flashing (the formation of vapour bubbles

that affect the rotor speed on turbine meters).

Meters are proved before they are overhauled or serviced. When

operating conditions change, meters are proved at least once or twice

a month.

TURBINE & POSITIVEDISPLACEMENT

METERS

METER ACCURACY


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A meter proverconsists of a piece of pipe with two detectorsmounted inside separated by a fixed distance. Meter provers check

the accuracy of meters: a known volume is passed through the meter

prover (to or from) a meter at normal operating conditions and

accuracy is determined by comparing the known volume with the

volume measured by the meter.

In order to keep the line running at peak efficiency, operations must

know what is going on at stations along the pipeline and must be

familiar with applications for the various control instruments. An

understanding of how different control devices and systems work

allows operations to maximize flow and equipment performance and

anticipate upset conditions before they occur. As well, suchunderstanding ensures that operations is familiar with how station

controlling devices react and are able to maintain an efficiently

functioning line if the station loses contact with the Control Centre.

Pipeline control systems include control equipment based on

operational commands. Pipeline control systems also automatically

monitor and control the pipeline to ensure that the line operates

within preset limits.

A control system is a system in where a value is measured (for

example, the setting of a pressure control valve), compared against a

preset value or set point and a responding action is taken. A

feedback control system is a closed loop type of control system inwhere information is fed back into the control system. Figure 18 is

an illustration of a simple feedback control system.

Figure 18Simple Feedback Control System

37


METER PROVING

CONTROLSYSTEMS &INSTRUMENTATION

DEFINITION OF ACONTROL SYSTEM

Action isTaken

Controller ComparesReading to Preset Value

InstrumentReading


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The three parts of a control system are sensors, controllers, and finalcontrol elements (refer to Figure 19).

Figure 19Three Main Parts of a Control System

The start and end points of control systems are the sensors. Sensors

report what is happening in the pipeline so that the PLC

(programmable logic controller) can respond. The PLC evaluates the

information and sends a command in response. The final control

element actually carries out the command. The sensors then register

the change and send the information back to the PLC.

Sensors, the PLC and the final control elements work together to

allow remote control of pipeline systems, thus allowing controllersto spend more time actually overseeing efficient gas movement.

Ideally, control systems would prevent all upset conditions. However,

several factors can affect and inhibit the control system's ability to

monitor and control operations. These factors include:

The time lag between the time that the sensors detect a condition

and the PLC initiates a command to correct the condition.

A dead band, which is the distance a device can move within

mechanical linkage before it begins triggering a reaction. Dead

bands increase the time lag of control systems, and also prevent

control systems from recording very small changes in variables.

Many instruments and devices work together to ensure that the

pressure in the pipeline remains near the set point.


Controller Final Process Sensors Control Elements Disturbance

Pressure PLC PCV Transmitter

Discharge

Set Point

from SCADA

PARTS OF A CONTROLSYSTEM

HOW A CONTROLSYSTEM WORKS

PROBLEMS INCONTROL SYSTEMS

PRESSURE INSTRUMENTS& CONTROL SYSTEMS


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Three types of devices are used to measure line pressure: a Bourdontube, bellows, and diaphragm.

A Bourdon tube is a curved, flexible tube connected to the linkage

at one end and open at the other. Liquid enters the open end of the

tube and causes the tube to straighten. The movement of the tube

turns a dial that indicates pressure.

A bellows consists of a metal chamber or bellows with corrugated

sides. A bellows works according to the same principles as the

Bourdon tube but is generally more accurate.

A diaphragm type of pressure sensor resembles a small box. Gas

flows into the box and presses against an internal membrane causing

a dial to move and sending an electric signal to the Control Centre.

In addition to pressure sensing devices, pressure control systems are

also equipped with pressure switches and pressure transmitters.

Pressure switches are devices used for high and low alarms for

equipment protection.Pressure transmitters monitor pressure in a

reading that is converted in the PLC.

The basic parts of a pressure control system are:

a suction pressure transmitter system

discharge pressure transmitter system

a programmable logic controller (PLC), and

the pressure control valve.

Figure 20Basic Pressure Control System

PRESSURE INSTRUMENTS

BASICS OF THE PRESSURECONTROL SYSTEM

PLC

DischargePressure

TransmitterSystem

SuctionPressure

TransmitterSystem


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The Controller receives the discharge and suction pressure setpointsfrom the Control Centre, and the actual discharge and suction

pressure levels from the sensors on the pipeline. The PLC then

determines the difference in values between actual levels and set

points, and sends signals to the control elements. The larger the

difference, the more the control elements (for example, a PCV) will

be required to move to attain the setpoint.

The PLC generates an error signal when there is a difference

between a setpoint and a reported value: the larger the difference, the

stronger the error signal.

Thepressure control valve is the final control element in the suction

and discharge pressure transmission system. The PLC increases and

decreases the line pressure by adjusting the PCV to achieve a

setpoint. An electro-hydraulic actuator is a device that hydraulically

opens or closes a valve in response to an electrical signal.

Gas is highly flammable and the threat of fire is always present. A

fire could have extremely serious consequences, ranging from

damaged equipment and lost throughput to loss of life. Therefore,

fire and gas detection systems are installed to generate alarms and/or

shut down equipment and pump stations in the event that either fire

or high levels of combustible gases are detected.

There are four types of fire detection systems: Heat detection systems that sense rising temperatures.

Smoke detectors: ionization type detectors detect the products of

combustion, while the photoelectric type is triggered when its light

beams are blocked by visible smoke.

Ultraviolet (UV) light detectors that detect fire UV radiation.

Infrared detectors, which are used to detect combustion of most

light hydrocarbons, excluding methane.

Figure 21Four Detector Types:Heat, Smoke,Ultraviolet, andInfrared

PRESSURE CONTROLVALVES

FIRE & GASINSTRUMENTS &

CONTROLS SYSTEMS


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Fire detection systems initiate different responses from the PLC,depending upon the location of the fire. For example, the PLC may:

initiate alarms (local and/or remote)

shut down compressors, shut down circuit breakers, open bypass

valves, close station and isolation valves

shutdown ventilation fans

activate foam, water or other deluge systems, and

send an alarm to the SCADA system.

Figure 22Fire Control Systems

Combustible gas detection systems detect leaks from piping or

equipment installed in compressor stations. There are two alarm

points associated with combustible gas detection:

20% LEL (lower explosive limit) 40% LEL.

When 20% LEL is reached, alarms are generated and fans start.

At 40% LEL, additional alarms are generated and compressors

shut down.

Since compressors are complex and expensive pieces of equipment,

numerous monitoring and detection systems are in place to shut

down compressors to avoid possible damage in the event of upset

conditions. These detection systems monitor for temperature,

vibration, and pressure.

PLC

Detector Action

Inputs Controller Outputs

The PLC determinesthe output based

on the input.

FIRE CONTROL SYSTEMS

GAS DETECTION SYSTEMS

COMPRESSOR &MOTOR INSTRUMENTS& CONTROL SYSTEMS


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The temperature of compressors and motors can be measured withthree instruments: thermometers, thermocouples, and resistance

temperature detectors (RTDs).

High compressor temperatures may mean:

the bearings have either lost their lubricant or have failed, and/or

the compressor or motor is vibrating excessively.

High motor temperatures may mean:

a bearing has failed

the compressor has mechanical problems, and/or

the ambient air temperature and humidity is too high.

Vibration is the back and forth motion a machine exhibits in a

resting position. Excessive vibration could seriously damage

expensive compressor units. Vibration can be caused by:

an imbalance in the motor

cracked or worn bearings

misalignment of the coupling between the motor and the

compressor.

Most motor protection is done with a type of computer assisted relay

system designed to detect situations where a motor could sustain

damage.

Motor protection systems monitor:

the temperature of the motor

internal pressure

lube oil pressure

unit vibration.

If a motor protection relay senses that a motor is heating more

quickly than normal, the system shuts down the motor before

damage occurs.

TEMPERATUREINSTRUMENTS

VIBRATION DETECTION &CONTROL SYSTEMS

MOTOR PROTECTIONRELAYS


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1. Regarding custody transfer, any losses or gains resultingfrom inaccurate measurement are the responsibility of the_______.

a) gas production company

b) transmission company

c) end customer

d) government

2. The piece of equipment used to ensure meter accuracy isthe ______.

a) turbine engine

b) positive displacement meterc) prover

d) pressure transmitter

3. The start and end points of a control system is a(n)_____.

a) actuator

b) transmitter

c) sensor

d) push button

4. A Bourdon tube measures __________.

a) temperatureb) pressure

c) level

d) concentration

5. What is the purpose of pressure switches?

a) initiate high and low alarms

b) suppress high and low alarms

c) start a compressor

d) stop a compressor

43


REVIEW 4


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44

6. The programmable logic controller (PLC) __________.a) works with sensors to control day to day operating

b) maintains optimum operating in spite of process disturbance

c) is adjusted by the controller to maintain optimum flow rates

d) compares information from sensors to set points, then takes

described action

7. __________ are used for detecting fires.

a) UV light detectors that detect UV radiation from fires

b) infrared detectors that detect combustion of most light

hydrocarbons, except methane

c) smoke detectorsd) heat detection systems that sense rising temperatures

e) all of the above




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Valves are a crucial part of pipeline operations because they direct

the flow of gas in the pipeline. Although Controllers do not control

all valves on the pipeline, they must understand each type of valve

and its behaviour. The Controller uses valves to direct flow, regulate

flow, and control pressure. Valves protect the pipe and compressors

from over-pressurization. Understanding the function, purpose, and

behaviour of valves enables the Controller to detect possible

problems and implications for line operations.

The correct use and operation of valves is essential to the successful

execution of every procedure and manoeuvre in the pipeline system.

Knowing the location of block valves and check valves can help the

Controller minimize the amount and impact of a leak.

One factor of valve selection that controllers must be aware of is the

long-term flow forecasting. Equipment is purchased on the basis of

long-term forecasting of greatest flow rates, and the equipment

presently used may be oversized in anticipation of future higher flow

rates. Equipment only suited or sized for todays flows or pressurescould cause future restrictions on throughput, and require expensive

repurchase of equipment in the future.

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

Identify the main components of valves.

Describe the basic components of valves and their function.

Describe typical valves used for isolation and blocking and their

applications.

Describe operating considerations for each type of isolation and

block valve.

VALVESSECTION 5

INTRODUCTION

OBJECTIVES


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A valve is a device that controls gas flow through the pipeline. Whena valve is completely open, gas flows unimpeded through the

pipeline. When a valve is partially opened, it has a throttling effect

on the gas flow. When a valve is closed, no gas can pass through that

section of pipe.

The typical valve components are:

valve body

valve bonnet

closure member

valve stem, and

seat, seals, seating rings (valve trim).

Figure 23Typical ValveThe plug valve is shown with the common major components labeled. These

components include: body, bonnet, closure member, valve stem,

seals/seating ring, and seat.


BASIC VALVECOMPONENTS

Valve Body

Closure

Member

Plug Port

Seal

Bonnet

Valve

Stem


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The valve body is the shell of the valve that houses the closuremember. The valve body provides structural support for the valve,

and is the part that is physically attached to the pipeline. The shape

of the valve body helps determine how gas flows through the valve.

The valve bonnet is the cover of the valve. Maintenance staff open

the bonnet to service the valve.

The closure member, often called the closure device, is the physical

barrier used in the valve. The closure member opens or closes as

required by the controller to stop flow, throttle flow or let flow

completely through. Valves are often named according to the type of

closure member they use.

There are three types of closure members: gate, ball and plug.

The closure member is connected to the actuator by the valve stem.

The actuator raises, lowers or rotates the valve stem, which causes a

corresponding change to the closure member. Manual actuators can

be attached to the valve stem. Valves can be classified according to

how the valve stem moves the closure member.

The valve seatis inside the valve body, next to the closure member.

The seating ring and/or seals help hold the closure member against

the seat. They provide a tight seal between the valve and the seat so

there is no leakage when the valve is closed, and no seeping of gasinto the valve body when the valve is open.

The valve trim is the removable part of the valve, such as the closure

member, the seats, seals and seat/or seating rings .

Remote actuators are used to control valves in the field. Remote

actuators translate the electrical signal sent from the PLC (in

response to a command sent from the control centre) into physical

energy. When the actuator receives a signal from the PLC, the

actuator opens or closes the valve.

VALVE BODY

VALVE BONNET

CLOSURE MEMBER

VALVE STEM

VALVE SEAT

VALVE TRIM

ACTUATORS


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Electro-mechanical actuators are used most often when the speed ofthe valve opening or closing is not critical, and when the valve is not

opened or closed too often. Electro-mechanical actuators are NOT

used on pressure control valves. Pressure control valves use electro-

hydraulic actuators.

Valves used for isolating pipeline sections are ON/OFF-type valves.

An ON/OFF valve is operated in a fully open or fully closed position.

Figure 24Electro-mechanical Actuator

In a typical pipeline system, electro-mechanical actuators use small motorsto operate isolation and block(ON/OFF) valves,

There are three types of ON/OFF valves used in the pipeline system:

Gate valves have "gates" that lift or lower to open or close the

valve. Gate valves are used to isolate sections of pipeline and

compressor stations for maintenance or operational reasons.

Plug valves are valves that open or close by rotation of a plug

moving perpendicular to the pipe wall. Plug valves are used for

isolation, metering and delivery applications, where accuracy

regarding the amount of gas delivered is required.

Ball valves are similar to gate valves except that their closuremember is spherical and the cavity through the ball is round. Ball

valves are occasionally used on meter and tank manifolds, and are

commonly used on instrument lines.

ISOLATION &BLOCK VALVES


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In addition to isolation and sectionalizing valves, there are ON/OFFvalves used in the pipeline system that perform related, but more

specialized functions. These special purpose valves are as follows:

Check valves are used to prevent back flow, and are opened by the

pressure of the gas flowing in one direction. Check valves have no

external valve stem or actuator. They are opened by the pressure of

the gas flowing from upstream to downstream.

Check valves are used:

with gate valves downstream of major river crossings to prevent

reverse flow of gas into the river if a line ruptures

at strategic locations along the pipeline in case of line rupture

at environmentally sensitive locations

between the suction and discharge lines on a compressor unit bypass

to prevent recirculation of gas

downstream of booster pumps (with a gate valve) to prevent back

flow when the compressor is turned off, and

downstream of tanks to prevent back flow into the tank.

Figure 25Flapper Check ValveWhen the gas flow is in the correct direction, the hinged flapper remains open.

When flow reverses direction, the hinged flapper closes and stops the flow.

49


Liquid Flow

Open Closed

SPECIAL-PURPOSE VALVES

CHECK VALVES


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50

1. A valve is a device used to ___________.a) block flow through the pipe line when closed

b) measure the pressure of gas in the pipeline

c) lift or rotate a closure member

d) help maintain turbulent flow

2. A valve whose closure member is a sphere with a cylin-drical cavity milled through it is called a ________.

a) plug valve

b) ball valve

c) gate valve

d) check valve

3. Check valves onlyclose when ________.

a) backflow occurs

b) there is low gas flow

c) the controller sends a command to close them

d) they are manually closed

4. The valve whose main purpose is to prevent gas backflowis called a ________.

a) pressure relief valve

b) check valve

c) isolation valve

d) stopple valve



REVIEW 5


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51


Variable speed drives can be grouped into two types, based on how

they function. The two types are variable frequency drives (VFDs) for

electric motors, and variable speed drives (VSDs)for diesel or

gasoline motors. Since there are no diesel- or gasoline-powered

motors on gas transmission pipelines, this section describes how the

VFD regulates rotational speed, helps to reduce repair and mainte-

nance costs, and increases operating efficiency.


objectives.

Understand the components and operation of a variable frequency

drive (VFD).

VARIABLE SPEED DRIVESSECTION 6

INTRODUCTION

OBJECTIVES


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52


A variable frequency drive (VFD) is a type of variable speed drivethat controls the speed of an electric motor by adjusting the

frequency of AC power used by the motor. VFDs are installed on

electric motors to optimize power use and minimize energy costs.

The use of VFDs facilitates engine startups and shutdowns. VFDs

can be installed in conjunction with PCVs. In such installations, the

VFD regulates energy while the PCV dissipates energy.

Energy can be saved by slowing down the compressor to match the

pressure required to compress gas through the pipeline. By slowing

down a compressor, every 100 horsepower saved is significant and

the saving is often several hundred horsepower per compressor per

year. Under VFD control, the motor only uses as much energy asneeded to drive the compressor and produce the required pressure.

The operational speed of an electric motor depends on how fast the

stators electromagnetic field rotates. The speed that the stators

electromagnetic field rotates is dependent upon the frequency of the

current flowing through the stator windings. Pipeline compressor

motors often are three-phase motors. A three-phase motor is an

electric motor that uses three-phase alternating current to rotate the

magnetic field of the stator. Three-phase motors have sets of

windings spaced equally apart in the stator.

The purpose of a VFD is to increase or decrease the speed of

rotation of the stators electromagnetic field, by increasing ordecreasing the frequency of the AC power going to the stator. This

increases or decreases the speed of rotor rotation. Since the

compressor and the rotor shaft of the motor are solidly coupled, the

VFD speeds up or slows down the compressor by adjusting the

frequency of AC current going to the motor.

One VFD system can supply the necessary frequency to several

compressor units. The VFD is configured to make sure the

compressors keep working even if the VFD is out of service.

With a conventional unit start, there is a large initial rush of current

VARIABLEFREQUENCY

DRIVES (VFDS) ELECTRIC

HOW VARIABLEFREQUENCY DRIVES

OPERATE


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that may cause winding insulation breakdown and eventual motorfailure. With a VFD, AC power is increased gradually until the motor

has reached full speed. This gradual powering up is termed a soft

start. Using the VFD to slow the motor before stopping it reduces

motor wear. This is called a soft shutdown.

Figure 26

Windings in a Three-Phase Motor Stator

53


Phase 1

Phase 2

Phase 3

C


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54

1. Under ________ control, the compressor motor uses onlythe amount of energy required to drive the compressor andto produce the required pressure.

a) PCV

b) diesel

c) Controller

d) VFD

2. The purpose of the ________ is to increase or decreasethe speed of rotation of the stators electromagnetic field,by increasing or decreasing the frequency of the AC powergoing to the stator.

a) three-phase

b) controller

c) VFD

d) diesel motor

3. The term ________ describes how a VFD is used togradually increase AC power until the motor has reachedfull speed.

a) ramping

b) soft shutdown

c) soft startd) throttling

4. The variable frequency drive is a type of ________.

a) compressor motor configuration

b) PCV

c) gasoline engine

d) diesel engine

Answers are at the end the module.


REVIEW 6


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In the pipeline industry, electricity is the most widely used energy

source, driving everything from large industrial motors to heating

and lighting equipment. The purchase of electrical power is also the

primary cost involved in the operation of a pipeline. Knowledge of

the fundamentals of electricity, its generation and transmission, and

electrical power management techniques assists the safe and efficientoperation of the pipeline.


objectives.

Recognize the fundamental properties of electricity.

Identify the components of an electrical circuit.

Relate voltage, current, and resistance using Ohms Law.

Identify AC, DC, and three-phase power.

Identify electrical generating and transmission systems.

Recognize various electrical load types.

Explain system control, protection and efficiency.

Identify the fundamentals of electrical energy management.

INDUSTRIAL ELECTRICITY &ELECTRICAL POWER MANAGEMENT

SECTION 7

INTRODUCTION

OBJECTIVES


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To understand the fundamentals of electricity, the Controller must beaware of its source and basic properties. It is essential that

Controllers be familiar with basic atomic theory, this section

provides an introduction to electrons, the forces that move them, and

the materials that carry them.

The building blocks of the material universe are atoms which

contain a nucleus of protons and neutrons, as well as orbiting

electrons. The electrons are held to the atom by their attraction to the

protons in the nucleus. Electrons orbiting furthest from the nucleus

often break free from the atom and travel to join neighbouring

atoms, as shown in Figure 27. This movement of electrons is the

basis of electricity.

A flow of electrons is known as electrical current. Current ( I ) is

expressed in amperes (A,) which is a measure of the flow rate of

electrons.Materials in which electrons are free to move easily are

said to be good electrical conductors. Conversely, materials in

which electrons are not free to move easily, such as porcelain, are

said to

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