- Published on Sunday, 13 April 2008 15:08
- Written by Mark Clark
Expansion of oil and gas production into remote and inhospitable areas of the world challenges actuator manufacturers to produce rugged, reliable and often specialized products to meet the pipeline industry’s needs.
A number of specialized designs of valve actuators have been developed over the years to cope with specific valve control demands that are found in the pipeline industry. Examples include gas-over-oil, high-pressure gas and electro-hydraulic actuators, as well as specialized hydraulic actuators designed for subsea valves.
While the fundamental principles of design for these actuators are well established, rapidly advancing technologies, increasing demands for reliability, reduced maintenance and automation from end-user industries continue to present manufacturers with new challenges. In addition, the expansion of oil and gas production into increasingly remote and previously unreachable areas, combined with the growth of strategic pipeline distribution networks across remote and inhospitable landscapes, places further pressure on the manufacturer to provide rugged and reliable valve actuation solutions.
Testing for Reliability in the Extreme
The importance of testing cannot be over emphasized, not only to prove the long-term performance and reliability of products, but also to gain specific approvals from end-user markets without which it would be difficult or even impossible to bid on projects.
Some major equipment manufacturers’ testing policies are designed to reassure the customer that the quality of its product range is first class through the achievement of internationally recognized quality assurance approvals for design and manufacture.
Running in parallel with these assessments, equipment manufacturers also subject their products to the test procedures required for end-user approvals in specific markets and industrial disciplines. In these areas there have been significant market-led increases in activity in recent years.
In addition to the hyperbaric testing of subsea actuators and performance verification of gas-over-oil actuators mentioned later in this article, testing programs in recent years have expanded to include specific tests such as:
- IP66M/67M, dust, water jet, immersion and deluge testing of pneumatic actuators
- Shell qualification for hydraulic and pneumatic actuators
- Transco qualification for hydraulic actuators
- HIPPS (high integrity pressure protection systems) qualification for control systems
- GOST Russian Certificate of Conformity and Federal Use Permit
- ABS (American Bureau of Shipping)
These are in addition to ATEX explosion-proof certification, PED (European Pressure Equipment Directive) approval and SIL (safety integrity level) assessments that also apply to pipeline actuation products.
Subsea Actuators, Testing In-depth
Subsea valve applications, which often involve vital fail-safe and associated safety-related duties, represent an area of technology demanding the very highest levels of quality and product integrity to ensure reliable long-term performance. It may be prudent to not only test to API (American Petroleum Institute) qualification but also to achieve third-party-witnessed hyperbaric approval to the international qualification procedure ST-028.
In one API test performed by a major equipment manufacturer, a scotch-yoke hydraulic actuator with ROV (remote-operated vehicle) override was operated in a hyperbaric chamber under an external pressure of 3600 psi (240bar-g) to represent the submerged qualification depth of 2,400 meters over a period of six weeks. The actuator was selected as a representative sample of all the company’s subsea actuators for the purpose of the testing, which was witnessed by a third-party inspector. The severity of the testing reflects the crucial nature of subsea actuator duties and the increasing depths at which actuators are expected to perform as exploration moves into new, more remote offshore fields.
In the ST-028 hyperbaric test a similar hydraulic actuator fitted with a limit switchbox was subjected to cyclic testing to prove its suitability for submerged installation at a depth of 45 meters. The witnessed testing included pressurizing the switchbox with air at 75 psi (5bar-g) without any sign of leakage or bubbles, static torque and cycle testing of the actuator at ambient and 75 psi (5bar-g) external pressure (1,090 cycles at 2400 psi [160bar-g] on each test), final static torque monitoring, strip down and inspection. This was a much shorter test, taking only three days to complete, although the combined total operating test, amounting to over 2,000 cycles, is representative of a much longer working life.