In the final part of the series, Paul Shillito, engineering director at Oliver Valves, looks at the importance of testing when it comes to reliability.
We’ve previously looked at cathodic protection and how to reduce hydrogen stress cracking. Another important factor for manufacturers and clients is that a particular valve will function correctly once in position on the seabed having proven itself under simulated test conditions.
For this purpose, we conduct the tests in a hyperbaric chamber, which provides external pressure equal to or greater than that which will be encountered on location.
At depths of 10,000ft – around the current limit for most subsea pipelines – the pressure is approximately 4,500 psi, or more than 300 times atmospheric pressure at the surface.
Dynamically testing the valve – opening it and closing it repeatedly – under simulated temperatures and pressures both internally and externally is the only way to be sure that no unacceptable leak paths are present and that the valve will cycle freely. Any resistance could potentially cause the actuating spindle to shear, or in the case of hydraulically actuated valves, fail to either close or open resulting in complete loss of function.
The results of these tests form the basis of a Failure Mode, Effects, and Criticality Analysis (FMECA) exercise, which takes the probability of any individual component in the system failing along with the level or risk presented by that failure, to give an overall reliability estimate.
Safety at the core of subsea valve development
As global energy companies continue to extract oil and gas from reserves deeper under the sea, the demands on pipeline technology get greater and valve manufacturers are responding by working to continuously develop and improve the reliability of their products.
Adding to this, the Deepwater Horizon explosion and the subsequent flow of oil from the Macondo well have brought the eyes of the world’s media onto the safety procedures that are in place for subsea operations. Together with the wider industry, safety is our number-one concern and we work hard with our clients to ensure everything possible is done to minimise risk.