Study on Safety Performance of Nitrogen Sealing in Inner Floating Roof Tank

Pilot operated pressure relief valves installed on cryogenic storage tanks may chatter as a result of inaccurate plant design or sudden construction changes on site. If the situation persists, possible consequences include extensive cost increments in replacement and repair as well as delays in the start-up of new facilities. Even though extensive research has been conducted on pressure relief valve chatter and theoretical mathematical models have been derived, some plants seem to ignore the basic results of these studies.

Chattering pilot operated valves may not provide sufficient relieve capacity resulting in overpressure and imposing safety risks to the facility. Lessons learned and providing support in solving these issues is the main focus of this paper.

It is known that relief valve instability and chatter is a dynamic problem which requires an understanding and coupling of the pressure source (e.g. the cryogenic storage tank), the inlet line, the pilot operated pressure relief valve and the discharge line.

This paper presents research results as well as extensive field experience on the insurgence of valve chattering on a dedicated flow test facility with ambient air and gases at cryogenic temperatures.

Best design practice is going to be provided and differences between standard pilot operated relief valves and those using dampening systems will be demonstrated. This new generation of pilot operated valves is less susceptible to chatter and hence reduces potential risk for the protected equipment, the environment and coworkers.