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Industrial Safety

Failure to replace corroded pipe led to 2019 explosion in Philadelphia

US Chemical Safety and Hazard Investigation Board urges refineries to replace hydrofluoric acid

by Jeff Johnson, special to C&EN
October 12, 2022 | A version of this story appeared in Volume 100, Issue 37


First photo shows ruptured pipe elbow atop debris from explosion. Second photo shows rusty pipe elbow with a big opening in it setting by itself on a bench.

Credit: US Chemical Safety and Hazard Investigation Board
This corroded pipe elbow, shown in explosion debris (left) and in the CSB laboratory (right), caused a 2019 explosion at a Philadelphia refinery.

Failure to replace a nearly 50-year-old corroded pipe elbow in a Philadelphia refinery led to a 2019 fire and explosion that endangered 117,000 people living nearby, according to a US Chemical Safety and Hazard Investigation Board (CSB) report.

Five workers sustained minor injuries from the incident at the Philadelphia Energy Solutions refinery. The incident cost the company $750 million. The refinery is shuttered and the company has filed for bankruptcy.

Given the refinery’s urban location, the incident could have been much worse, Steve Owens, CSB interim executive authority and board member, says. “It should be a wake-up call to industry.”

The accident began in the refinery’s hydrofluoric acid (HF) alkylation unit, where extremely toxic HF is used to boost gasoline octane. The CSB determined that a steel pipe installed there in 1973 ruptured. The pipe contained high levels of nickel and copper, which was acceptable when the pipe was installed. Today, pipes with high amounts of these metals aren’t used because they don’t meet current international industrial standards, which were updated in 1995.

The company took no action despite federal Occupational Safety and Health Administration and Environmental Protection Agency regulations requiring reevaluation of equipment such as piping, says CSB supervisory investigator Lauren Grim.

In its report, the CSB urged the American Petroleum Institute to update several of its voluntary standards for refinery HF alkylation units. It also recommended that the EPA require refinery owners to consider inherently safer approaches and to move away from HF use. Alternative alkylation technologies, such as a solid acid catalyst or an ionic liquid acid catalyst, are available, the report notes.

During the Philadelphia refinery incident, the corroded pipe elbow ruptured. A large vapor cloud—composed of about 95% propane, 2.5% HF, and the remainder of other hydrocarbons—engulfed part of the unit and ignited within 2 min, the report says.

Some 2,376 kg of HF was released. Although some of the HF was captured, 1,484 kg was released to the atmosphere. Also, some 307,000 kg of hydrocarbons were released, but most was combusted.

A safety system was activated but the operator was unable to remotely turn on water pumps and cannons to suppress airborne HF. Eventually, a worker manually turned on pumps and cannons to reduce HF air emissions.

The incident triggered several explosions, which spewed vessel fragments. One, weighing 17,000 kg, cleared the nearby Schuylkill River. Two others landed in the refinery.

The fire burned through the night before firefighters contained it.


The headline of this story was updated on Oct. 14, 2022, to indicate that the company's failure to replace a pipe, not just the pipe itself, was blamed for a 2019 explosion and fire in Philadelphia.



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