Date: 27/05/2023
Pipe elbow had become severely thin from HF corrosion and ruptured to initiate the incident on 21 June 2019.
On the morning of June 21, 2019, a pipe elbow in the Philadelphia Energy Solutions (PES) hydrofluoric acid (HF) alkylation unit ruptured. A large vapor cloud—composed of about 95% propane, 2.5% HF, and other hydrocarbons—engulfed part of the unit. The vapor cloud ignited two minutes after the start of the release, causing a large fire. The control room operator then activated the Rapid Acid Deinventory (RAD) system, a safety system that causes HF to be routed to a separate drum in the event of a loss-of-containment incident or other emergency. The activation of the RAD system successfully drained about 339,000 pounds (43,260 U.S. gallons) of hydrofluoric acid from the unit to the RAD drum.
Three explosions then occurred in the unit. Evidence indicates these explosions were secondary events caused by the fire. The third explosion was the largest and occurred when a vessel, called V-1, containing primarily butylene, isobutane, and butane, violently ruptured. A fragment of the V-1 vessel weighing approximately 38,000 pounds flew across the Schuylkill River, and two other fragments, one weighing about 23,000 pounds and the other 15,500 pounds, landed in the PES refinery.
The HF alkylation unit was severely damaged by the fire and explosions. Marsh JLT Specialty reported that the incident resulted in an estimated property damage loss of $750 million. Five workers and a firefighter experienced minor injuries during the incident and response.
Mechanical Integrity. A steel pipe elbow containing high concentrations of nickel and copper had become severely thin from HF corrosion and ruptured to initiate the incident. Carbon steel with high nickel and copper content is known within the industry to corrode faster from contact with HF than carbon steel with lower nickel and copper content. While the PES pipe elbow had become severely thin from corrosion, adjacent piping components lower in nickel and copper content had not corroded as quickly and were not thin. At the time of the incident, published industry standards and recommended practices did not require refineries to conduct 100% component inspection of carbon steel piping in HF service to identify any piping components corroding and thinning faster than others, which as shown by this incident, can lead to hazardous loss of containment events. After the incident, API RP 751 Safe Operation of Hydrofluoric Acid Alkylation Units was revised to include a new requirement for refiners to develop a special emphasis inspection program to inspect all individual carbon steel piping components and welds in identified HF alkylation corrosion zones to identify areas of accelerated corrosion. This new requirement should help prevent future failures of steel piping with high nickel and copper content in HF alkylation units.
https://www.csb.gov/philadelphia-energy-solutions-pes-refinery-fire-and-explosions-/