(79a) Avoiding EARLY Relief from LPG Storage Tanks

This paper deals with the scenario of early vapor relief from LPG storage tanks in winter, when ambient temperature may fall below the dew temperature in the head space. If that occurs, some liquid may clog the relief valve sensing line, increase the pressure in the dome of the pilot, and lead to the unintended early pressure relief. Incidents in the industry are known when pilot operated relief valves start to relieve at pressures 30% - 40% below the intended set pressures.

Though API 2000 7th Ed. (2014) and ISO 28300 (2008) provide generally good guidance in the application of pilot operated relief valves for protection of cryogenic storage tanks, some guidance on good design practices to avoid early relief of cryogenic media is missing. This paper will share lessons learned and best design practices to avoid such unpredicted events.