Philadelphia — The Chemical Safety Board will begin “looking more closely” at hydrofluoric acid in the refining process, CSB interim Executive Authority Kristen Kulinowski said during an Oct. 16 news conference on a June 21 explosion and fire at a Philadelphia refinery.
Announcing the release of a factual update and a new animation detailing the incident at the Philadelphia Energy Solutions Refinery, Kulinowski also noted the “need for more robust reviews of (the) corrosion mechanism.”
According to the agency, the incident likely was caused by a pipe elbow in the refinery’s alkylation unit that had corroded to about “half the thickness of a credit card.” More than 5,000 pounds of hydrofluoric acid was released from the pipe and formed a cloud, which ignited in minutes and resulted in a massive explosion and fire.
“Since 2015, the CSB has investigated three major incidents at refineries that utilize HF for alkylation,” Kulinowski said in an Oct. 16 press release. “Incidents in Superior, WI, and Torrance, CA, fortunately did not result in an HF release. That was not the case here in Philadelphia. 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.”
CSB’s other findings:
- 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.
- Although 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 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 Philadelphia 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 refinery.
“Corrosion is not a new issue for the CSB,” Supervisory Investigator Lauren Grim said in the release. “In [a] 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.”