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Background

Double-block-and-bleed and double-

isolation-and-bleed valve configura-

tions are used to define a certain level

of isolation in a pipeline. Once imple-

mented, a section of the pipeline sys-

tem is isolated to facilitate maintenance

of the pipeline section. These valves

can be used to reduce the volume of

fluid that is released in the event of a

pipeline failure. They are an important

component that ensures safe operation

of a pipeline. However, they do not pre-

vent pipeline failures and cannot fully

mitigate the consequences of a pipeline

Isolation Basics: Effective Isolation of Liquid Pipelines

PART

TH

REE

Double block and bleed and double isolation and bleed valve configurations are used to define a certain level of isolation in a pipeline. Once implemented, a section of the pipeline system is isolated to facilitate maintenance of the pipeline section. These valves can be used to reduce the volume of fluid that is released in the event of a pipeline failure. They are an important component that ensures safe operation of a pipeline. However, they do not prevent pipeline failures and can not fully mitigate the consequences of a pipeline failure. Valves are largely part of the response in the event of a pipeline failure.

By Stephen Johnson, Gobind Khiani & James Chau – Fluor Canada

failure. Valves are largely part of the re-

sponse in the event of a pipeline failure.

Through the use of two separate block

valves and a bleed valve, a pipeline sec-

tion can be isolated. The main function

of this installation is to prevent fluid

from getting into an area where main-

tenance work is being completed. These

block valves (often ball type) are closed

when isolation needs to take place. The

bleed valve is subsequently opened to

vent the cavity. The line downstream

is depressurized and maintenance can

be performed on this section of pipe. If

any fluid leaks past the first valve, the

bleeder valve functions to drain the

fluid before the fluid pressurizes the

cavity. In the event the bleeder valve

is plugged, the downstream valve pre-

vents fluid from getting past it even fur-

ther downstream.

Application of Standards

The National Energy Board (NEB) re-

quires that companies under regula-

tion place valves for pipeline control

and pipeline failure impact reduction.

Valves are strategically placed and take

the terrain into consideration. Strate-

gic placement is required, especially in

high consequence areas such as rivers

and crossings.

CSA Standard Z662-15 indicates that

isolating valves are to be used for pipe-

line maintenance and for response to

operating emergencies. The standard

specifies certain details with regards to

the location of these valves. When de-

termining the number and spacing of

sectionalizing valves, an engineering

assessment must take place and con-

sider factors such as:

• The amount of potential fluid release

due to maintenance blowdowns,

leaks or ruptures

• The nature of the fluid potentially re-

leased

• Impact of the release (i.e., how wide-

spread the fluid will travel and how

hazardous the fluid is)

• Time to drain an isolated section

• Effect on inhabitants in the area

• Future development in the area

• Continuity of service of the pipeline

• Operations and maintenance flexibility

When this engineering assessment is

not conducted, spacing follows the Z662

standard. Refer to Figure 1 for maximum

valve spacing as per the standard’s re-

quirement. The maximum spacing in

between valves for high vapor pressure

(HVP) pipelines may be adjusted based

on operational, maintenance and design

considerations, but shall not exceed 15

kilometers. The location of the isolation

valves along the pipeline focus on areas

where maintenance occurs frequently.

These types of areas include tank farms,

metering skids and relief systems. Tanks

often require maintenance to monitor

the condition of tank vents, drains and

valves. These components are essential

to provide proper storage of fluid in the

tanks. Metering skids often determine

flow and regulate pressure. Skids re-

quire maintenance as well in order to

keep optimal pipeline operability. Thus,

maintenance of the meters and control

valves are required. Isolation can be

used in the meter calibration market.

Each closed valve in the system must

seal tight as small leaks can produce er-

rors in the meter calibration and incor-

rect calibration can cost the end user

large sums of money. Using these iso-

lation strategies helps lessen the risk

of leaks and ensures correct calibration

of the meter. Isolating relief systems

are important to confirming if the relief

configuration is still working properly

– namely the relief valve. These relief

valves are crucial to prevent overpres-

sure in the pipe and prevent potential

ruptures and pipeline leaks.

The class location refers to the devel-

opment within the area being assessed

(i.e., where the pipeline will be installed).

As shown in Figure 2 for CSA Z662-15,

there are four main class designations.

Class 1 entails the least development.

Each subsequent higher class number

has more development. Development

refers primarily to the number of dwell-

ing units and the area is categorized as

such. Higher class numbers consist of

higher risk areas. Therefore, the maxi-

mum valve spacing is lessened.

However, CSAZ662-15 refers mainly to

valve and isolation placement based

on the receptors in the area. Recep-

tors are based on the population in

the surroundings. Terrain and special

crossings (e.g., rivers) should also be

considered. Therefore, there is an op-

portunity to optimize valve placement

so that effective isolation can take

place when needed. CSA Z662-15 pro-

vides a good standard rule of thumb

to follow when there is nothing out of

the ordinary along the pipeline right

of way. However, do not blindly follow

this rule of thumb and place valves at

certain distances all along the right of

way. This approach can lead to high

costs and not provide much additional

isolation benefit.

Figure 1. Maximum Valve Spacing along a Pipeline as per CSA Z662-15

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As the pipeline enters high conse-quence areas, more strategic place-ment of isolation valves is required. For example, if a pipeline were to enter a double-sided valley that con-tained a river, isolation valves would need to be placed on each side of the water body. Oil flows downhill due to gravitational effects. The valves pre-vent the oil from reaching the sec-tion underneath the water body. This placement ensures that the water body is isolated if an incident occurs and acts as protection. See Figure 3 for a representation of this setup.

Strategic valve placements promote a higher safety standard and help opti-mize costs. With some special areas of terrain, such as hills, valves are not re-quired, as the terrain acts as a natural isolation point for the pipe sections downstream.

In some instances, one must determine which pipe section is more important to be isolated. One example is where one section has a more hazardous liq-uid or gas. Prioritize which sections of pipe should be isolated based on fluid of the pipe, impact of the release, spe-

cial terrain, etc.

Why Pipeline Isolation?

Double-block-and-bleed and double-isolation-and-bleed configurations are used in pipelines to ensure a high safe-ty standard. The fluid in the system can be blocked and prevented from reach-ing components further downstream.

The blocked fluid can then bled off. They can be used to isolate pipeline sections in the event of leaks, thereby minimizing the impact. Isolation can also assist in pipeline maintenance and if certain components need to be test-ed. If double-block-and-bleed and dou-ble-isolation-and-bleed configurations are not installed, the pipeline runs the risk of failing to contain spills. Spills can be very costly and have a large societal and environmental impact if left uncon-tained. These types of configurations help minimize the impact. Therefore, codes and standards have established a certain requirement for isolation and these valve configurations.

Pigging Application

In some instances pipelines cannot be thoroughly inspected using operation-al pigs. This situation can be due to the pipeline having unpiggable compo-nents. Pipelines can be designed to be “piggable”. But, pigging facilities may not always be in place. Therefore, dou-ble-block-and-bleed and double-iso-lation-and-bleed valve configurations may be utilized. Through two separate block valves and a bleed valve, pres-sure can be regulated in pig launchers and receivers. These block valves are closed and the bleed valve is opened to relieve any excess pressure that may be in the pigging components. Once the pressure is relieved, proper maintenance can be performed on the pigging equipment to ensure sound pipeline operability.

Figure 2. Class Location Designations

Figure 3. Double-Sided Valley with Isolation Valves

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The process of pigging involves insert-ing devices, known as scrapers or pigs, into crude or natural gas pipelines via pig launchers. The pig travels through the line without interrupting flow and, depending on its design, can perform a number of tasks including cleaning, liq-uid removal or inline inspections to de-termine remaining wall thickness or in-line anomalies. The pig is received and removed from the line at pig receivers that are isolated from the main fluid flow path. Pigging for cleaning or liquid removal is performed either manually or automatically.

Manual pigging is a labor-intensive process that can be cost-prohibitive, especially in applications where exces-sive fluid accumulation requires mul-tiple cleaning pigs to be launched daily. Recently, due to the economic condi-tions and drive for capital efficiency, most pipeline operators have sought to improve flow efficiencies, reduce operations and maintenance costs and eliminate the extensive time and man-power requirements associated with manual pigging. Automated pigging is becoming more popular as a method to achieve cost-saving efficiencies.

Manual Pigging Versus Automated Pigging Systems

Manual scraping/pigging sys-tems consist of a launcher unit at the start and a receiver unit at the end of the section of pipeline to be pigged. The units are isolated from the pipe-

line with valves. This isolation allows pressure to be released and product drained or vented. Pigs can then be inserted and extracted safely by an operator through a door at the end of the launcher/receiver. The systems are designed to load, launch and retrieve a single scraper/pig at a time.

Automated pigging systems allow for multiple pigs to be loaded simultane-ously. This approach eliminates the need to blow down the scraper/pig barrel and vent pipeline contents every time a pig is released. Labor costs are reduced, safety is improved and the need to open and close valves and doors when launching is minimized. Automated sys-tems can be operated remotely or set on a timer, which allows operators to initi-ate launches remotely and minimizes the risk of mishaps due to unexpected complications in the field.

ABOUT THE AUTHORS

Stephen Johnson is a Chemical Engineer by education, and has been working in the field of Process Safety Management since 1992. His professional experience is focused on hydro-carbons & petrochemicals, but has also included agricultural chemicals, forest products and the food industry. Primary technical activities include all areas of risk engineering - qualitative, semi-quantitative and quantitative risk assess-

ments, consequence modeling, and noise modeling. Stephen is currently the Sr. Fellow - HSE Director at Fluor Canada Ltd.

Gobind Khiani, M.Eng., P.Eng. has served in engineering and project management roles for both operating and EPC companies. He has a bachelor’s degree from the University of Pune in India and a Master of Engineering from the Uni-versity of Calgary in Alberta, Canada. Currently, he is the Fellow Piping Valves with Fluor in the piping materials en-gineering group. He is a chairman of Calgary Branch Execu-

tive Committee at the Association of Professional Engineers and Geoscientists of Alberta and Valve Users Group and Vice Chairman of International Standards Organization, representing Canada.

James Chau, E.I.T. has worked in engineering roles for engi-neering, procurement and construction (EPC) companies, as well as operating companies. He has a bachelor’s degree in Chemical Engineering with a specialization in Energy and En-vironment from the University of Calgary in Alberta, Canada. Currently, he is an associate pipeline design specialist at Fluor in the pipeline department. James has experience in pipeline

Please see Part Two of this series in the October issue of Valve World Americas journal.

REFERENCEShttps://internationalpipelineexposition.com/wp-content/uploads/sites/7/2016/08/White-Paper-Retrofitting-pigging-functionality-in-unpiggable-pipelines.pdf

https://internationalpipelineexposition.com/wp-content/uploads/sites/7/2016/08/White-Paper-Double-Block-and-Bleed.pdf

http://www.subseauk.com/documents/presentations/double%20block%20and%20bleed%20isolation%20-%20oga%20kl%202013.pdf

http://valvemagazine.com/web-only/categories/technical-topics/4638-the-true-meaning-of-double-block-and-bleed.html

Page 107 CSA-Z662-15

https://www.enbridge.com/projects-and-infrastructure/public-awareness/intelligent-valve-placement