WHERE VALVES ARE USED

Pipeline Valves—Always ReadyШАБЛОНЫ YOOTHEMEШАБЛОНЫ НЕДВИЖИМОСТИ JOOMLADetails 

Published on Monday, 07 November 2011 10:46 Written by Greg Johnson

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This nation is crisscrossed by hundreds of thousands of miles of crucial pipelines that transport vital feedstock from

sources to the places where it’s transformed into fuel and products. For the valve industry, that translates into millions

of dollars of business.

According to Hart Data and Mapping Services, the United States has over 700,000 miles of crude oil and natural gas

pipelines—about 100,000 miles of crude onshore pipelines and over 600,000 miles of onshore gas pipelines. This

number stands to greatly increase as drilling in the various shale plays across the continent occurs. These seemingly

endless strings of pipe have one thing in common: They all contain large numbers of valves optimized for pipeline

operating conditions.

WHAT’S IN A PIPELINE?

Both quarter-turn and multi-turn block valves as well as check valves are used in pipeline service. Those built for gas

or crude oil pipeline service are designed and tested in accordance with the American Petroleum Institute (API)

specification 6D “Pipeline Valves.” The document, which is also published by the International Organization for

Standardization as ISO 14313, includes requirements for gate, ball, check and plug type valves. Prior to the mid-

1950s, the choice of valve for use in pipeline blocking applications was easy—gate valves were used because the

pipeline ball valve had not been invented yet. Some plug valves also were used back then, but the majority of the

designs for these valves were reduced-port type that were not piggable.

The term “piggable” has nothing to do with breakfast meat choices. Rather, it means being “pig-capable”—in other

words, the devices designed to clean or inspect the interior of the pipeline (the “pigs”) also may be passed through

the bore of the valve without catching on a reduced bore or other interior projection in the valve. A requirement in API

6D gate valves is that their inside bore dimensions are precisely specified to allow this passage of pigs.

With the advent of quality pipeline ball

valves over the past few decades, sales of pipeline gate valves have fallen. Meanwhile, pipeline ball valves, which

are trunnion style, are now making inroads in all types of pipeline service, particularly in natural gas. Still, holdouts

exist.

“Some companies are staunchly entrenched in the gate valve,” according to David Fehrenkamp, a senior sales

engineer with Cameron. He also adds that “in many natural gas pipeline operations, quarter-turn has taken over

100%.”

So why do many pipeline owners favor the gate valve for pipeline service? Product pipelines that carry fluids such as

gasoline, distillates, diesel fuel and other finished petroleum products are a popular place for the rough and ready

gate valve. “We use slab gate valves for most of our main line valves, but we do use expanding gate valves on our

product line from Texas City to Pasadena,” says Billy Daigle, maintenance services specialist for Marathon Pipe Line

LLC (MPL). “We use expanding gate valves for station isolation valves and pig launchers. Pig launcher and receiver

service is harder on valves because of the debris from the pigging operation, so we choose expanding gates because

of their toughness,” he adds.

Ball, check and manifold valves are commonly used in pipeline service.

The quarter-turn vs. gate valve debate gets hotter when cost becomes the prime factor for selection. The quarter-turn

trunnion pipeline ball valve is much cheaper to make than the jumbo-sized gate valves, with their large and expensive

body castings. Another factor that tips the pendulum toward quarter-turn pipeline valves is the availability and delivery

of quarter-turn products. Because drilling in the shale plays across the country is exploding in terms of how fast it’s

occurring, Fehrenkamp says the requests from customers for delivery time is “rush, rush, rush, I need it now!” A

domestically produced trunnion pipeline ball valve can be built in roughly four weeks, which is about the time needed

to get a good gate valve casting under the luckiest of circumstances. An additional four to six weeks might then be

required to complete the gate valve machining, assembly and testing.

Details 

Published on Monday, 07 November 2011 10:46 Written by Greg Johnson

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Some explanation is in order when speaking of pipeline gate valves. Gate valves used in this service are different

from the wedge-type gate valves common in the downstream petrochemical and refining industries. The pipeline

gates come in two basic types: slab and expanding wedge. The slab type utilizes a large slab that floats slightly in the

valve body and seals downstream with the aid of upstream pressure. Spring-loaded seats are often employed to

increase the sealing efficiency. The expanding gate, on the other hand, uses a split-disc design and separator

mechanism that tightly expands the gate both upstream and downstream as the valve is closed. This type then

reverses the process upon opening. The tighter closing design enables the valve to seat more effectively at lower

pressures.

A QUESTION OF INTEGRITY

Valve integrity along with pipeline integrity is of prime importance to the pipeline owner as well as those who live and

work close to the line. A complex formula for risk assessment is used to guide pipeline operators with inspection

programs. The assessment criteria include the product, age of the pipeline, and proximity to population centers, local

housing and occupied structures. The pipeline itself must be inspected at specified intervals. This line inspection is

usually performed by “smart pigs,” complex devices that roll through the line to perform radiography, remote visual,

ultrasonic evaluation and other inspections.

Pig launchers are hard on valves because of the debris from the pigging

operation.Valves, on the other hand, need their own inspection programs. The U.S. Department of Transportation has

developed natural gas pipeline valve inspection criteria detailed in CFR Title 49, part 192, “The Transportation of

Natural and Other Gas by Pipeline: Minimum Federal Safety Standards.” Paragraph 192.745 of that title states, “Each

transmission line valve that might be required during any emergency must be inspected and partially operated at

intervals not exceeding 15 months, but at least once each calendar year.” Similar requirements are published for

crude oil and hazardous liquid pipelines in CFR Title 49, part 195, “Transportation of Hazardous Liquids by Pipeline,”

paragraph 195.420.

Proper valve maintenance is always vital, and pipeline valves are no exception. Since most pipeline valves have a

seat sealant injection feature to facilitate tight closure, the sealant must be properly introduced into the seat seal area.

New valves typically require more sealant top-off than those that have been in operation for a year or two.

Pipelines use a variety of valves to control fluids both above and below the ground.All

pipeline operators have preventive maintenance (PM) and repair programs to ensure the life and functionality of their

valves. Most companies will use a combination of in-situ repair along with shop refurbishments for tough repair cases.

“We spend over 25% of our time in valve shops to get the valves just like we want them,” says MPL’s Daigle.

Because of the importance of proper pipeline valve repair, a specification that describes the repair procedure is in

place: API 6DR, “Repair and Remanufacture of Pipeline Valves.”

HOW PIPELINES WORK

Understanding how pipelines operate provides a better understanding of how valves are used in pipeline service.

Major pipelines receive input from either smaller gathering lines, tank farms or, in the case of finished products,

refineries and petrochemical plants. Because of friction losses, the arriving pressure of the fluid is much too low to

provide enough energy to send the product very far through the line. Most transmission pipelines in the United States

operate at maximum pressures of less than 1440 psi. Common maximum target pressures range from 700-725 psi

and 1300-1400 psi, which equates to ANSI classes 300 and 600 respectively. These maximum pressures would only

be found immediately downstream of pumps or compressors.

Because of the pressure drop in the line, booster pumping stations at intervals along the line are needed. In the case

of a liquid such as crude oil, a minimum pressure of about 25-50 psi is needed for the suction side of the booster

pumps to operate. Each booster pumping station is equipped with manifolds containing many valve types, including

gate, ball, check, and in areas where pigging is not required, reduced port, lubricated plug valves. Additionally, control

valves often are used to regulate flow from the stations.

Published on Monday, 07 November 2011 10:46 Written by Greg Johnson

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The most common pressure class for pipeline transmission lines is class 600, which has a working pressure of 1440

psi. The valve ratings are in accordance with The American Society of Mechanical Engineers (ASME) standard

B16.34 and API 6D.

Valves play a critical role in keeping the nation’s pipelines safe.Although a number of

valves are in operation at each pumping station (for liquids) or compressor station (for gas transmission), the critical

valves in a pipeline are spaced along its route. They serve as blocking or isolation valves to segregate pipeline

sections for required maintenance or to help in cases of an accident. The minimum required spacing of these valves

is prescribed in ASME B31.4, “Gas Transmission & Distribution Piping Systems” and ASME B31.8, “Pipeline

Transportation Systems for Liquid Hydrocarbons & Other Liquids.”

Several factors influence valve spacing, including: 1) the amount of potential fluid leakage, 2) the impact of a release,

3) future development in the pipeline area, and 4) the time required to blow down (empty) an isolated section. Other

criteria include how close the line is to occupied buildings and houses. According to B31.4, the distance between

block valves could be as little as four miles apart for a gas pipeline.

Slab gate valves are used along the pipeline systems.Liquid pipelines

have their own criteria for valve placement. They are placed: 1) at the suction end and discharge ends of a pump

station, 2) on each line entering or leaving a storage tank area, 3) on each mainline at locations along the pipeline

that will limit damage or pollution from accidental hazardous liquid discharge, 4) on each lateral take-off from the

trunk line, 5) on each side of a water crossing that is more than a 100 feet wide, and 6) on each side of a reservoir

holding water for human consumption.

Additionally, check valves may be installed on grades and the downstream side of rivers and streams for more

protection from backflow conditions in case of a line breach.

Many block valve installations are outfitted with automatic shutdown controls. These controls are set to close the

valve if pressure or flow rates change, indicating a possible breach in the line. By having these valves spaced

throughout the line, the amount of potential fluid leakage that might occur during a line break is limited. Additionally,

many pipeline valves are designated as emergency shutdown valves (ESD), which are remotely operated from the

pipeline control center.

These block valve location requirements account for the numerous small, fenced-in valve installations visible when

driving around areas with many pipelines—numerous pipeline block valves are located above the ground for easy

maintenance. However, some are buried, with only the operating mechanism and auxiliary lubrication and bleed lines

showing. These installation areas used to be the exclusive domain of gate valves. However, today welded body

trunnion-mounted ball valves are very popular, especially for clean natural gas transmission lines. The unique welded

body construction eliminates the potential body-bonnet leak path, while the only remaining leak path is up through the

packing area.

Though fugitive emissions (FE) leakage has been a focal point in the refining industry for over 20 years, the upstream

and midstream markets have been fairly immune from FE scrutiny. However, that situation is changing. According to

MPL’s Daigle, “LDAR [leak detection and repair] for pipelines is becoming popular and required, especially since

packing leaks are the most common leaks we deal with.”

One place where emissions of any type are unacceptable to almost everyone is in undersea pipelines. Because they

are surrounded by water and vibrant marine life, undersea pipelines certainly have their own set of challenges.

However, there are other key differences from on-land pipelines that affect design, including the design of the valves

attached to the pipelines.

For example, undersea pipelines that connect wellheads to gathering points often operate at much higher pressures

than their onshore counterparts. It is not uncommon for these lines to see 10,000 psi. Valves designed for this

submerged service are critical, purpose-built flow control devices that absolutely must work properly when called

upon to operate. Because of the unique undersea environment, standard API 6D requirements are not deemed tough

enough, so a special underwater valve specification was written to cover these products: API 6DSS “Specification for

Subsea Pipeline Valves.”

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TESTING

Although interior pressures are also quite high in subsea pipelines, it is sometimes the outside pressure from the

extreme depths that introduces the most stress on valves and piping. As a result, pipeline valves designed for

installation at great depths are often tested in a hyperbaric chamber, where extreme pressure is exerted on the

outside of the valve, while the inside is sealed against the external pressure.

All pipeline valves receive seat and shell tests per API 6D or 6DSS, not unlike their downstream counterparts, which

are usually tested in accordance with API 598, “Valve Inspection & Testing.” One difference between the two testing

documents is that, with API 6D pipeline valves, the holding times for the tests are much longer. For example, a 24-

inch valve shell tested per API 598 requires a five-minute duration, while the same size valve tested per API 6D

requires a 30-minute duration. These longer holding times for pipeline valve tests are often extended into hours by

the supplementary test requirements of many pipeline owners.

While pipelines and pipeline valves lie mostly invisible beneath six feet of earth or under 600 feet of ocean, they are

nonetheless highly “visible” when an accident occurs. As a result, pipeline valves are closely scrutinized members of

the valve family. They are built to tougher standards and must work every time because they must protect lives and

property that lie near their installations. Pipeline valves could borrow the Latin motto of the United States Coast

Guard, which is “Semper Paratus,” which means: always ready.