Catastrophic equipment failure due to overpressure can potentially occur in the event of compression system discharge, interstage, and/or suction check valve failure, coincident with compressor shutdown. Depending on system design and application, overpressure values approaching or exceeding 300% of equipment design are possible. Comparatively, for some equipment even limited overpressure can result in catastrophic vessel failure due to brittle fracture. Additional hazards associated with compression system fail-to-check scenarios include risks associated with excessive flare loading and compressor rotor reverse rotation. In the case of an ethylene refrigeration compressor at a typical ethylene plant, rotor reverse rotation can potentially exceed over-speed limits.
This paper summarizes the risk assessment results based on analysis performed on the three primary compression systems within six different ethylene plants. The methodology used to assess associated risks and system dynamics is presented. Alternative methods for mitigating risks are also discussed along with check valve reliability data. An overview of applicable overpressure protection requirements defined in the ASME Boiler and Pressure Vessel Code is provided. This paper will be of interest to anyone that designs or operates multistage compression systems in the chemical, petrochemical or refining industries.