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22/09/2011
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Level control has been identified as the runaway most challenging offshore valve application, according to Severn Unival.
 A study of data from the past 15 years, by the engineering specialist, reveals that it has been commissioned to repair or retrofit more than 1,000 OEM level control valves ranging from one to 24 inches bore – more than double the number of valves in other severe or critical offshore applications that have needed similar attention.
"For instance, choke valves are the next most volatile, with over 450 repairs or retrofits completed in the same timeframe," explains Severn Unival's sales manager for North Sea Services, Andy Woodward.
Why the difficulties? Woodward points to the fact that level control valves are used in the process of stripping impurities – usually water and gases – from the oil stream before it is shipped from the platform for sale or production.
"The stream is sent through a series of separators and it is essential that levels of oil and water are carefully managed. But certain level control applications can put valves under a lot of stress," he states.
They can be exposed to severe flashing and vibration, caused by fluctuations in vapour pressure, themselves due to the many constituents of the oil. High velocities of flashing vapour can cause extensive erosion of internal components.
This exacerbates the erosive qualities generally associated with offshore oil extraction, due to sand and salt content of the stream. Results can be catastrophic, seriously compromising safety, integrity and reliability.
Hence Woodward is advisijng platform managers to ensure level control valves are a top priority for maintenance strategies. "Our repair intelligence data clearly indicates that level control valves are the number one 'bad actor' of North Sea platforms," he says.
"Aging assets are becoming the norm in this region, so it is more important than ever to take proactive measures to optimise performance," he adds.
What's more, Woodward suggests that shrewd repair and retrofit activity can also cost-effectively raise the performance standard of these aging assets.
"Technical solutions deployed by Severn Unival can range from simple overhauls to the use of more sophisticated trim designs for specific level control applications," he explains.
"Improving the trim with higher grade materials such as ceramics or tungsten carbide can also enhance the longevity of valves," he continues. "High-level technical engineering can bring robust, long-term solutions. Identifying, and focusing attention on, gruelling applications like level control plays an important role in maximising offshore uptime."
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Author
Brian Tinham
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