place: API 6DR, “Repair and Remanufacture of Pipeline Valves.”
Above: Pig launchers are hard on valves because of the debris from the pigging
operation. Right: Valves play a critical role in keeping the nation’s pipelines safe.
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.
All pipeline operators have preven-
tive maintenance (PM) and repair pro-
grams to ensure the life and functionali-
ty of their valves. Most
companies will use a com-
bination of in-situ repair
along with shop refurbish-
ments 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.
Pipelines use a variety of valves to control fluids both above and below the ground.
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 prod-
ucts, refineries and petrochemical
plants. Because of friction losses,
the arriving pressure of the
fluid is much too low to pro-
vide 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. Com-
mon maximum target pres-
sures 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.
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.
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
