Applications

The AE leak detection technique has been applied to the following applications:

• Detection and quantification of losses to flare via relief, vent and blowdown valves. Remedial action has environmental as well as economic benefits
• Losses around compressor recycle loops have been detected, unchecked these losses reduce compressor efficiency and increase power consumption
• The testing of relief valves to determine if they have reseated following lifting in service
• The detection and trending of leakage in valves subject to sandy service. Erosion of valves due to sand has led to losses of containment and unplanned platform shutdowns. The use of the AE technique, in conjunction with other sand indicators such as sand probes and sampling can identify those valves at risk, ensure they are monitored to provide a "comfort" factor and ensure any redesigned valve performs. The AE technique has been applied to separate drains, level and interface control valves and to desanding and dewatering units
• Monitoring of Riser ESDVs in conjunction with their annual leak test. This has provided data for input into the predictive equation. Also the AE technique has been used to check the boundary valves which are required to isolate each ESDV from the platform during the leak test. This ensures the test result is not distorted by leakage in or out the isolated inboard section
• The AE technique is beiing considered as a method of enabling compliance with the Prevention of Fire and Explosion, and Emergency Response (PFEER) Regulations. PFEER requires the operator to establish written schemes of examination and maintenance for the safety critical elements in their plant, and to set and demonstrate compliance with appropriate performance criteria. Many ESDVs, blowdown and relief valves will be included as safety critical elements. Future work will involve the preparation of AE test regimes to meet the required performance criteria allowing for the AE technique's uncertainty.

Score has carried out surveys on thousands of valves covering above applications on a variety of different offshore installations. Typically 30 to 70 valves can be surveyed per shift depending on location, ease of access, lagging, and operational support. Databases of test results have been built up which enable long term trending on large valve populations to be carried out. This information, together with the specific valve duties and valve specifications, enables recommendations to be made regarding future valve specification, maintenance philosophy and strategic spares holdings and optimised valve management strategies.