Failure Probability and Inspection Interval of Pressure Safety Valves: Case Study of a Gas Processing Plant

Abstract

Inspection of pressure safety valves (PSVs) is critical for the safety of process plants which also involves cost. API proposes a Risk-Based Inspection (RBI) method that includes consequences and probability of failure. In this work, PSVs installed in different pressurized equipment of a gas processing plant located in Comilla, Bangladesh, have been studied in order to establish and implement a risk-based inspection planning process in the facility in accordance with API 580 and 581. The probability of failure and consequence of failure have been assessed separately and then combined to determine the risk of failure. The results have been used to assess the acceptability of the current inspection schedule in the facility and present some inspection planning guidelines in order to manage risks. The outcome indicates that a large fraction of the overall risk is concentrated in a relatively limited number of PSVs. These potentially high-risk PSVs should require greater consideration through an amended inspection plan in which more regular inspections are to be scheduled for these devices while inspection intervals may be extended for PSVs identified as having lower risk.