Extending Pressure Relief Valve Inspection Intervals by Using Statistical Analysis of Proof Test Data

This paper correlates as-received relief valve test results with current inspection intervals and presents conclusions based on statistical analysis. During the past three year period over 500 used valve proof test records from a site population of 3500 safety relief valves were acquired and reviewed. Collection and analysis of spring-loaded relief valve test data continues with the goal being to increase the test intervals within guidelines, reduce costs, and maintain safety margins. Based on current test intervals of 1–7 years, time in service appears to have a minimal effect on valve performance. Seat material and inlet size are identified as having a statistically significant impact on valve performance. An increase in TP/SP of 1–2% per year was noted for soft seated, small inlet sizes. Photographs of failed valve internals and discussion of failure causes are included.