Federal investigators believe a rupture pipe elbow was at fault in a June 2019 explosion and fire at the Philadelphia Energy Solutions refinery in Pennsylvania, according to the U.S. Chemical Safety Board.
The rupture released process fluid containing hydrofluoric acid that, in turn, formed a flammable vapor cloud. Only minutes later the vapor ignited.
Measurement of the ruptured pipe elbow shows that it had corroded to only 0.012 of an inch thickness, about half that of a credit card and 93 percent thinner than PES’ own requirement to be replaced. Operating pressure at the time of the release was estimated at 380 pounds per square inch.
Investigators issued their initial findings during a news conference in Philadelphia Oct.16.
PES estimated that about 676,000 pounds of hydrocarbon were released overall, most of which burned. An estimated 5,239 pounds of corrosive and toxic hydrofluoric acid was also released, of which only 2,000 pounds was recovered and processed through the refinery wastewater treatment system.
HF is classified by the U.S. National Institute for Occupational Safety and Health (NIOSH) as “immediately dangerous to life or health at levels above 30 parts per million (PPM).
“The CSB is unaware of any offsite or onsite health impacts from the hydrofluoric acid release,” the report states.
Within two minutes of the first rupture the released vapor ignited a large fire in an alkylation unit used to convert isobutane and low-molecular-weight alkenes into alkylate, a high-octane gasoline component. Inside the next quarter hour two large explosions rocked the unit.
Prior to the explosion, ultrasonic thickness measurements were routinely taken at designated locations along the piping as part of a company inspection program to monitor corrosion. However, the ruptured elbow was not one of those locations being monitored.
Installation of the ruptured elbow has been traced to about 1973 when the unit was originally built.
Piping failures due to corrosion played key roles in at least two refinery fires in the last decade. The 2012 Chevron Richmond, CA refinery fire was caused by a ruptured piping worn extremely thing by sulfidation corrosion. Likewise, the 2009 Silver Eagle refinery fire in Woods Cross, UT was also attributed to piping worn thin by corrosion.
However, the havoc at PES did not end with the two explosions in the alkylation unit. Twenty minutes after the initial explosion spreading flames triggered a third blast that shattered a massive feed surge drum, a device for fluctuations in the flow rate.
The blast hurled one 38,000-pound fragment of the drum complete across the nearby Schuylkill River. Two other fragments, one weighing about 23,000 pounds and the other 15,000 pounds, landed inside the refinery.
Flames were not brought under control until more than 16 hours after the initial blast. Within a week, PES announced that the refinery would be permanently shut down. The company declared bankruptcy several months later.
Work towards a final report on the refinery fire is ongoing, the CSB states.