HOUSTON (Reuters) - An ammonia cylinder burst late Monday while being heated as part of preparations to restart the alkylation unit at Marathon Petroleum Corp's 86,000 barrel-per-day Texas City, Texas, refinery, sources familiar with plant operations said on Tuesday.
Marathon spokesman Jamal Kheiry said the company responded to an incident at the refinery, in which there were neither injuries nor offsite impact.
Marathon was continuing the restart of the 10,000 bpd alkylation unit on Tuesday, said the sources, who requested anonymity because they were not authorized to speak to the media. The unit had been shut to repair pinhole leaks in piping.
The cylinder and the ammonia inside were being heated so the gas could be sent through the unit's piping to increase its temperature as part of the restart, the sources said.
Texas City residents took to social media after being shaken awake by the explosion shortly before midnight CDT on Monday (0500 GMT on Tuesday).
Bryan Rivera, assistant emergency management director for Texas City, said no alarms were sounded for residents because the incident posed no threat to them.
In a notice filed Tuesday afternoon with the Texas Commission on Environmental Quality, Marathon said the event that released 300 pounds (136 kg) of ammonia began at 11:37 p.m. and ended at 11:52 p.m.
"Ammonia cylinder found empty. Cause is under investigation," the filing read under the section to describe the cause.
Akylation units convert low-octane refining by-products into high-octane substances that are blended into gasoline.
The Texas City refinery is across the street from Marathon's 459,000 bpd Galveston Bay Refinery. The company is in the process of integrating operations of the two plants.
(Reporting by Erwin Seba; Editing by Richard Chang and Dan Grebler)