For a hydrogen production facility the feed gas and hydrogen product compressors are the heart of the plant, providing power to move gas through the process and the pipeline to the customers. If a mechanical problem occurs with in the running gear, machine vibration is the result. In the past our company viewed the vibration switches on a reciprocating compressor as equipment protection. A recent loss of containment incident changed that thinking. The incident at Air Products' Port Neches, Texas Hydrogen Pipeline Compressor Station in November 2006 caused us to rethink the way we install and test the vibration to motor trip interlock and start up a flammable gas reciprocating compressor after a vibration trip.

This paper outlines the use of an event tree quantitative risk analysis to determine the reliability required for the vibration switch, relay, and motor disconnect switch interlock for a Safety Instrumented Function (SIF). In addition to the SIF, administrative procedural changes were instituted to meet the hazard rate goal of the corporation. The demand on the SIF and administrative protection systems was based on one loss of containment incident for our fleet of 10,000 reciprocating cylinder operating years. Results of the quantitative risk analysis showed that the vibration trip needed to be redundant per cylinder and proof tested with the motor disconnect switch and interposing relay at least once every 2 years for a 6 cylinder compressor. Existing operating procedures were changed to include complete mechanical inspection and analysis of compressor operating data and start-up of the compressor on nitrogen after a vibration trip. Also new facility siting analysis excludes sensitive equipment and buildings from direct line up with the cylinder heads.

As a result of one loss of containment incident our company has upgraded the compressor vibration trip to a critical safety interlock requiring increased mechanical integrity testing with more stringent operating procedures and equipment layout.