The U.S. Chemical Safety Board (CSB) released a factual update into the June 21, 2019, explosion and fire at the Philadelphia Energy Solutions Refinery in Philadelphia, Pa. The update notes that a corroded pipe elbow appears to have ruptured in the alkylation unit, releasing process fluid that included over 5,000 lb of hydrofluoric (HF) acid. The leaking process fluid formed a large ground-hugging vapor cloud that ignited two minutes later, causing a massive fire and explosions.

While the CSB’s investigation is still ongoing, the factual update notes important details of the incident collected through interviewing witnesses, gathering evidence and piecing together the events that led to the explosion. Finding include:

  • The piping was susceptible to corrosion from the HF 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.