Valve Magazine - Fall 2011

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 engi-
neer 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 prod-
uct 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.

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

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

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.

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.

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

UPSTREAM, DOWNSTREAM, MIDSTREAM: WHAT’S THE DIFFERENCE? Those three terms are used all the time in the oil and gas industry, and although the definitions sometimes overlap, they denote specific areas on the oilfield to refinery trail:

Upstream: Starts at the bottom of the hole in the ground and covers most every-
thing on the wellhead up to the choke. The choke is a specialized globe valve that
is mounted on wellheads and is used to regulate the output of the well.
Midstream: Starts at the output of the choke and continues through all the sur-
face processing equipment and through the pipeline to the fence at the refinery.
In decades past, the term “midstream” was not in vogue, and everything was
either “upstream” or “downstream.” Now, midstream is used extensively.
Downstream: Generally speaking, everything inside the fence of the refinery.