At approximately 10:15 p.m. on Sunday, May 17, 2009, there was a sudden and large hydrocarbon release from a main process pipe in the Ethylene Unit at the Sunoco Marcus Hook, Pennsylvania Refinery. The release found an ignition source at an operating process furnace within 2 seconds, resulting in a fire. Seven other process lines within the pipe rack in the vicinity of the initial release ruptured from short-term overheating within the first 10 minutes. Fire fighting and process isolation efforts brought the fire under control, but it continued to burn for approximately 18 hours while process systems depressured. There were no injuries from the fire or the emergency response activities. There was significant heat damage to facility piping and equipment, and the event received media coverage and attention from regulatory agencies.
The initial release was from a pipe rupture 10” long by 7” wide on the bottom of the 10&' diameter (60oF - 475 psig) main process line. The cause of the failure was long-term localized external corrosion at a pipe support contact area. A loose steel quarter-sleeve was found under the pipe at the support location, with the dimensions of the sleeve being almost identical to the size of the localized thin area. This sleeve trapped moisture creating crevice corrosion between the sleeve and outside of the pipe. This sleeve also obscured the corrosion such that visual pipe inspections failed to detect the degradation. There was essentially no corrosion or thinning of the line outside of this sleeve crevice area during the 48-year service life.
The investigation identified the physical causes of the failure as well as design, inspection, maintenance, and operational work practice areas for improvement to prevent a similar failure in the future.
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