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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.
INTRODUCTION TO PIPELINE EQUIPMENT
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
INTRODUCTION TO PIPELINE EQUIPMENT
MODULE GOALS
INTRODUCTION
PREREQUISITES
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3
INTRODUCTION TO PIPELINE EQUIPMENT
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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4
GAS CONTROLLER TRAINING PROGRAM
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
INTRODUCTION TO PIPELINE EQUIPMENT
CONSTRUCTIONPREPARATIONS
MOBILIZATION
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6
GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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8
GAS CONTROLLER TRAINING PROGRAM
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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9
INTRODUCTION TO PIPELINE EQUIPMENT
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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10
GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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14
GAS CONTROLLER TRAINING PROGRAM
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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15
INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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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17
INTRODUCTION TO PIPELINE EQUIPMENT
Figure 14
Pipeline Construction Sequence
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GAS CONTROLLER TRAINING PROGRAM
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.
After this section, you will be able to complete the following
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.
19
INTRODUCTION TO PIPELINE EQUIPMENT
NATURAL GAS STORAGESECTION 2
INTRODUCTION
OBJECTIVES
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20
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 CONTROLLER TRAINING PROGRAM
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
INTRODUCTION TO PIPELINE EQUIPMENT
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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.
GAS CONTROLLER TRAINING PROGRAM
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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
INTRODUCTION TO PIPELINE EQUIPMENT
REVIEW 2
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25
INTRODUCTION TO PIPELINE EQUIPMENT
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.
After this section, you will be able to complete the following
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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GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
Stator CoreStatorLaminated Steel
RotorStator
Windings External Fan
Cast Iron FrameEnd Shield
Shaft
Bearings
Enclosure
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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
Answers are at the end of the module.
GAS CONTROLLER TRAINING PROGRAM
REVIEW 3
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33
INTRODUCTION TO PIPELINE EQUIPMENT
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.
After this section, you will be able to complete the following
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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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.
GAS CONTROLLER TRAINING PROGRAM
CUSTODYTRANSFER
MEASUREMENT
NET STANDARDVOLUME
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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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
INTRODUCTION TO PIPELINE EQUIPMENT
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.
GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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
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INTRODUCTION TO PIPELINE EQUIPMENT
REVIEW 4
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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
Answers are at the end of the module.
GAS CONTROLLER TRAINING PROGRAM
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45
INTRODUCTION TO PIPELINE EQUIPMENT
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.
GAS CONTROLLER TRAINING PROGRAM
BASIC VALVECOMPONENTS
Valve Body
Closure
Member
Plug Port
Seal
Bonnet
Valve
Stem
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INTRODUCTION TO PIPELINE EQUIPMENT
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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GAS CONTROLLER TRAINING PROGRAM
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
INTRODUCTION TO PIPELINE EQUIPMENT
Liquid Flow
Open Closed
SPECIAL-PURPOSE VALVES
CHECK VALVES
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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
Answers are at the end of the module.
GAS CONTROLLER TRAINING PROGRAM
REVIEW 5
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INTRODUCTION TO PIPELINE EQUIPMENT
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.
After this section, you will be able to complete the following
objectives.
Understand the components and operation of a variable frequency
drive (VFD).
VARIABLE SPEED DRIVESSECTION 6
INTRODUCTION
OBJECTIVES
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GAS CONTROLLER TRAINING PROGRAM
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
INTRODUCTION TO PIPELINE EQUIPMENT
Phase 1
Phase 2
Phase 3
C
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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.
GAS CONTROLLER TRAINING PROGRAM
REVIEW 6
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INTRODUCTION TO PIPELINE EQUIPMENT
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.
After this section, you will be able to complete the following
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