The US Chemical Safety and Hazard Investigation Board (CSB) has repeated its call for a review of refineries’ use of hydrofluoric acid (HF) and urged owners and regulators to conduct intensive inspections of all components. The board made the appeal Oct. 16 as it released an interim report on the cause of an accident at the Philadelphia Energy Solutions (PES) refinery, near downtown Philadelphia
The accident injured five workers. It began in the early-morning hours of June 21 in the alkylation unit, where HF is used to boost the octane of gasoline. It involved three explosions and a fire that burned for 24 hours. The largest explosion was in a vessel holding butylene, isobutane, and butane, which sent a 17,000-kilogram fragment across the nearby Schuylkill River.
The board found that a ruptured elbow pipe initiated the event. The elbow was part of a piping system that had been installed in 1973. The elbow had never been inspected, and the CSB found its thickness to be far below acceptable levels and about half that of a credit card. The CSB noted that two other similar accidents were caused by corrosion of high carbon steel when exposed to HF.
“Since 2015, the CSB has investigated three major incidents at refineries that utilize HF,” CSB interim executive authority Kristen Kulinowski says in a statement. Incidents at a Husky Energy refinery in Superior, Wisconsin, and an ExxonMobil refinery in Torrance, California, did not result in 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.”
HF is used in about one-third of the 150 US refineries. Fears of HF release in a dense, lethal, acidic cloud have led the CSB, communities, and members of Congress to call for better controls or substitution.
The CSB has urged the Environmental Protection Agency in particular to review its 25-year-old regulation of HF and begin a search for substitutes. The EPA has not initiated such a review.
At PES, some 307,000 kg of hydrocarbons was released, and most was combusted during the accident. Some 2,376 kg of HF was also released. Although some of the HF was captured and sent to a wastewater treatment system, 1,484 kg was released to the atmosphere.
Corrosion has frequently been a cause of refinery incidents investigated by the CSB. “In its prior investigation of a 2012 Chevron Refinery fire we determined that corrosion caused the rupture of a piping component,” CSB supervisory investigator Lauren Grim says in the statement. “Similarly, the 2009 Silver Eagle refinery fire was also caused by the failure of piping that had thinned due to corrosion.”
The CSB’s final report is expected early next year.
This story was updated on Oct. 23, 2019, to correct the identities, quantites, and fate of chemicals released in the PES incident. The story initially stated that 307,000 kg of HF was released rather than 307,000 kg of hydrocarbons and 2,376 kg of HF.