A Customized Solution
The 135-kilometer-long Shoukar-to-Hurghada pipeline is an important
strategic extension to the natural gas
distribution network in Egypt. Running
southwards along the western coastal
area of the Red Sea, the 24-inch-diame-
ter pipeline has an operating pressure of
1050 psi (70 bar) and is designed to
supply natural gas at a rate of up to
5MMSCMD ( 5 million standard cubic
meters per day) to power stations and
consumers in the provinces of Shoukar
and Hurghada.
The pipeline is owned by the gas
transportation company GASCO, which
was responsible for engineering, procurement, construction supervision,
commissioning and start-up. Construction of the $60 million project, which
began in May 2006, was completed in
2007.
Customized actuators were supplied
for block isolation valves, which enable
segments of the pipeline to be closed
down for maintenance, inspection and
safety reasons. For this application the
customer specified double-acting valve
operation under either local manual
control or remote electrical control,
with hydraulic manual override. In addition, each actuator is equipped with
enough accumulator capacity to complete four “stand-alone” valve strokes.
The valve manufacturer also specified
the torque output from the actuators
should be limited to prevent any risk of
damage to the valve stems. For this
function an innovative solution had to be
developed.
On the pipeline example above a
torque limiting device (TDL) was fitted
to limit the maximum torque output
from the actuator in order to prevent
damage to either the valve stem or the
actuator itself. Mounted between the
gas elements of the manifold block and
the gas/oil tanks, it works by measuring
and limiting the differential pressure
between the gas on the supply side and
the oil on the return side of the tanks.
As the amount of actuator torque is
directly proportional to this differential
pressure, damage to the actuator or
valve might occur if the differential
pressure becomes too great as a result
of unexpected resistance from the valve
during travel or when the actuator travel reaches the end stop bolts. Clearly,
the risk also increases in proportion to
the speed of valve operation, so the TLD
is pre-set to either the maximum torque
supported by the valve stem or the maximum allowable torque produced by the
actuator—whichever is the lower value.
When the differential pressure limit
is reached, the TLD blocks the gas supply and at the same time vents the pressure from the gas cylinder and gas/oil
tanks on the supply side, reducing to a
minimum the risk of damaging either
actuator or valve.
Electro-hydraulic actuators on pipeline
metering station
Gas-over-oil actuators during manufacture
The Electro-hydraulic Option
The increasingly popular electro-hydraulic option offers a self-contained
actuator package for pipeline valves,
operated electrically by means of an
integral hydraulic power pack and accumulator. Among other benefits, this
design enables fail-safe and emergency
shutdown duties to be performed by an
electrically powered actuator, with the
