tion component parts (solenoid valves, etc.), with marine quality stainless-steel solenoid valves specified for the ESD actuators in coastal locations.
The stroke (closing) time for ESD valves is 15 seconds while
the stroke time is 7 minutes for the mainline block valves. To
meet the block valve time—essential to prevent the risk of
pipeline damage—in the various ambient conditions encountered, special temperature and pressure-equalized throttle
valves are incorporated.
Each mainline block valve actuator is equipped with a position transmitter with eight position switches. The position
transmitter was required to be explosion-proof to EEx IIB
T4—which is the enclosure specification demanded for all electrical equipment on the actuators—and to utilize proximity
switching. Because a transmitter to this specification was not
readily available, the unit was custom designed specifically for
the contract and was Ex certified.
The eight switches on the mainline actuators provide fully
redundant positional control in four positions: fully open, 80%
open, 70% open and fully closed. The 80% and 70% positions
enable the actuator to be partially stroked for function test purposes, with position switch redundancy preventing the risk of
accidental valve closure and consequential pipeline damage.
Due to the pipeline’s geographical location the actuators are
fitted with earthquake-proof solenoid assemblies, each comprising two 90-degree-operated valves to prevent accidental
vibration-induced operation. For the mainline valves both normally closed (NC) solenoids must be energized to close the
valve, with each under the remote control of a separate PLC.
On the ESD valves both solenoids are normally open (NO) and
de-energizing either one will cause the valve to close, regardless of the continued presence of an electrical supply.
All the actuators are equipped with accumulators with the
capacity to provide three valve strokes without the motor and
pump running. In addition, provision is made to attach a
mobile pump to operate the actuator in the event of a motor
failure, while an integral hand pump is also fitted. All actuator
control packages are designed with full cathodic protection and
housed within a watertight stainless-steel cabinet.
Conclusion
The activities described above illustrate how the demands for
safety, efficiency and environmental responsibility from the
contemporary pipeline industry have a significant impact on
the valve actuator manufacturer, creating increasingly innovative design solutions, proven and supported by ever-more stringent testing. The constant expansion of oil and gas exploration
and production into more and more remote areas can only
increase all aspects of this activity for the actuator industry in
the foreseeable future. VM
MARK CLARK has worked in the industrial valve, actuation and instrumentation
industries in the United States and the United Kingdom for more than 35 years.
He is currently a freelance public relations consultant in the UK, specializing in
the valve actuation industry, and wrote this article on behalf of Rotork Controls.
