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
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,”
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
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.