CSB releases findings on massive explosion at PES refinery in Philadelphia

A pipe elbow, which had corroded to about half the thickness of a credit card, was the cause of the explosion and fire at the Philadelphia Energy Solutions (PES) refinery in Philadelphia, reported the Chemical Safety Board.

The pipe elbow ruptured in the refinery’s alkylation unit, releasing process fluid that included over 5,000 pounds of hydrofluoric acid, or HF. The leaking process fluid formed a large ground-hugging vapor cloud. Two minutes later, the cloud ignited, causing a massive fire and explosion, the agency said.

“Though the main tank holding HF was not breached, HF was a component of the process fluid released from the alkylation unit. We are lucky there were no serious injuries or fatalities,” said Interim Executive Dr. Kristen Kulinowski.

The agency released a factual update of the events that took place, which led to the explosion:

• The piping was susceptible to corrosion from the hydrofluoric acid that was in the process fluid. The elbow that ruptured corroded faster than the rest of the piping in this part of the process. 
• While pipe thickness in this section of the unit was periodically measured to monitor corrosion rates, the thickness of the elbow that failed had not been monitored for corrosion. The piece of piping that failed had a high nickel and copper content. Various industry publications have found that carbon steel with a higher percentage of nickel and copper corrodes at a faster rate than carbon steel with a lower percentage when used in a process with hydrofluoric acid.
• A secondary event at the PES refinery occurred when the V-1 Treater Feed Surge Drum ruptured, which launched a fragment of the vessel weighing 38,000 pounds across the Schuylkill River. Two other large fragments landed within the PES Refinery.

The fired occurred in June of this year, and the refinery has since closed.

CSB Supervisory Investigator Lauren Grim said, “Corrosion is not a new issue for the CSB. In its prior investigation of a 2012 Chevron Refinery fire, we determined that corrosion caused the rupture of a piping component.  Similarly, the 2009 Silver Eagle refinery fire was also caused by the failure of piping that had thinned due to corrosion.”The CSB’s interim animation details the events that occurred at the PES refinery on June 21^st, view the full animation HERE.

CSB noted that moving forward, a robust review of corrosion mechanisms, as well as the use of HF in the refining process, is needed.