Performance analysis of small size pilot plant and laboratory relief valves



Spring-loaded relief valves are one of the most common safety devices installed in pilot plants and laboratory bench-top units. They are typically used in sizes much smaller than those in process units, but their performance is assumed to be equivalent. Most organizations provide only limited preventive maintenance and re-inspection for these valves under the assumption that they are very reliable devices and operation is fairly assured.

Our experience and detailed test data with small size (1/2-inch and less) spring-loaded relief devices indicates that most will not perform as reliably as expected due to adhesion of the elastomer seal over time. This leads to initial relief pressures well over the 10% overpressure considered routine, with 30% overpressure being fairly common among certain sizes and conditions. Failing to recognize this problem can lead to otherwise preventable accidents, and even injuries.

Data on more than 1,000 relief devices in actual research service for several years was analyzed and the performance measured over time. The data clearly indicate the problem is endemic across all manufacturers and not easily solved. Results are presented in summary form to allow evaluation of the risk inherent in the use of these devices. It indicates a lower level of confidence in actual valve performance, as well as a need for more detailed hazard analysis and risk assessment of the potential for significant relief valve overpressure.