Auto-refrigeration of carbon-steel equipment during abnormal events is an ongoing concern in ethylene units. In late 2002, while changing out a power supply on the electronic governor for the propylene refrigeration compressor turbine drive at Chevron Phillips Chemical's Port Arthur Ethylene Unit, the turbine tripped resulting in loss of refrigeration to the ethylene fractionator overhead condensers. As the tower warmed up and the pressure increased, the pressure controlled flare dump valves and the pressure relief valves opened to the flare system. One of the pressure relief valves failed to close causing the tower to depressure down to 12 psig. This presented a potential brittle fracture hazard for an impact tested carbon steel tower.

The paper will review the response to this incident to bring the tower to a safe state as well as the mechanical reliability evaluation performed to ensure the tower was safe to re-pressurize and start up.

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