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Philadelphia Energy Solutions (PES) Refinery Fire and Explosions

Overview

On June 21, 2019, a pipe elbow in the Philadelphia Energy Solutions (PES) hydrofluoric acid (HF) alkylation unit ruptured. A vapor cloud of propane, hydrofluoric acid, and other hydrocarbons was released. The cloud ignited and led to a large fire and multiple explosions. The CSB determined that the incident was caused by rupture of a steel piping component with high nickel and copper content. The component had corroded from HF and thinned faster than adjacent piping components with lower nickel and copper content.

Incident Snapshot

Field Value
Facility / Company Philadelphia Energy Solutions Refining and Marketing LLC (PES)
Location Philadelphia, PA
Incident Date 2019-06-21
Investigation Status The CSB's investigation was released on October 11, 2022.
Accident Type Oil and Refining - Fire and Explosion
Final Report Release Date 2022-10-11

What Happened

  • On the morning of June 21, 2019, a pipe elbow in the Philadelphia Energy Solutions (PES) hydrofluoric acid (HF) alkylation unit ruptured.
  • At approximately 4:00:16 a.m., there was a sudden loss of containment causing flammable process fluid containing hydrofluoric acid to release from the PES alkylation unit, forming a ground-hugging vapor cloud.
  • A large vapor cloud, composed of about 95% propane, 2.5% HF, and other hydrocarbons, engulfed part of the unit.
  • The vapor cloud ignited about two minutes after the start of the release, causing a large fire.
  • At 4:02:37 a.m., the control room operator activated the Rapid Acid Deinventory (RAD) system, draining about 339,000 pounds of hydrofluoric acid from the unit to the RAD drum.
  • At 4:12 a.m., the control room operator tried to remotely turn on the water pumps that fed the elevated HF mitigation water cannons, but the water pumps did not turn on.
  • At 4:15 a.m. an explosion occurred in the unit.
  • At 4:19 a.m. another explosion occurred in the unit.
  • At 4:22 a.m., a third, and the largest, explosion occurred when the V-1 treater feed surge drum violently ruptured.
  • At about 4:39 a.m., the alkylation unit shift supervisor manually turned on the water pump that supplied the HF mitigation water cannons.
  • The fire was extinguished the following day, on Saturday, June 22, at about 8:30 a.m.

Facility and Process Context

  • Hydrofluoric acid (HF) alkylation unit at the PES Girard Point refinery.
  • The incident involved the depropanizer reflux line between V-11, the depropanizer accumulator, and T-6, the depropanizer distillation column.
  • The ruptured elbow was on the discharge piping of a pump that was not operating at the time of the incident.
  • The V-1 treater feed surge drum contained primarily butylene, isobutane, and butane.
  • The unit included the Rapid Acid Deinventory (RAD) system, V-10 hydrofluoric acid settler, elevated HF mitigation water cannons, and associated water pumps.
  • The piping circuit containing the ruptured elbow was installed in about 1973 and appears to have been original piping.

Consequences

  • Fatalities: 0
  • Injuries: Five workers and a firefighter experienced minor injuries during the incident and response.
  • Environmental release: PES estimated that 5,239 pounds of HF released from piping and equipment during the incident. 1,968 pounds were contained by water spray within the unit and processed in the refinery wastewater treatment plant. 3,271 pounds released to the atmosphere and was not contained by water spray. PES also estimated that about 676,000 pounds of hydrocarbons released during the event, of which an estimated 608,000 pounds were combusted.
  • Facility damage: The HF alkylation unit was severely damaged by the fire and explosions. Marsh JLT Specialty reported an estimated property damage loss of $750 million.
  • Operational impact: On June 26, 2019, PES announced that the refining complex would be shutting down. In February 2020, a U.S. bankruptcy court judge approved the sale of the PES refinery to Hilco Redevelopment Partners. As of the date of the report, Hilco Redevelopment Partners is demolishing the refinery and plans to repurpose the site.

Key Findings

Immediate Causes

  • The rupture of a steel piping component with high nickel and copper content that had corroded from HF and thinned faster than adjacent piping components with lower nickel and copper content.
  • The ruptured pipe released propane and toxic hydrofluoric acid to the atmosphere.

Contributing Factors

  • The lack of requirements by the American Petroleum Institute, Sunoco, and PES to inspect all existing carbon steel piping circuit components to ensure they could safely operate in HF service after the industry began quantifying the levels of nickel and copper in steel that could be considered safe for use in HF alkylation units in 2003.
  • The absence of remotely operated emergency isolation valves to isolate large sources of hydrocarbons.
  • Incident-induced damage to the water mitigation system that limited PES’s ability to suppress released HF during the incident.
  • The control system communication to the water pumps that supplied water to the elevated HF mitigation water cannons failed.
  • The uninterruptible power supply (UPS) also failed nine seconds later.
  • The water pumps that fed the elevated HF mitigation water cannons did not turn on when remotely activated.

Organizational and Systemic Factors

  • API RP 751, Sunoco, and PES did not effectively respond to advancements in industry knowledge by ensuring the safety of existing facilities through requiring all carbon steel piping circuit components to be inspected.
  • PES and the previous owner Sunoco never inspected all carbon steel components within the HF alkylation unit.
  • The applicable 1965 edition of ASTM A234 Standard Specification for Factory-Made Wrought Carbon Steel and Ferritic Alloy Steel Welding Fittings did not explicitly prohibit the addition of unspecified elements to steel, such as those specified in the YOLOY composition requirements.
  • The 5th edition of API RP 751 Safe Operation of Hydrofluoric Acid Alkylation Units contains gaps relating to the protection of control systems and backup power systems from fire and explosion hazards and the ability to isolate and stop releases from large hydrocarbon-containing vessels and all large inventories of HF using remotely operated emergency isolation valves.
  • There is currently no Federal regulatory requirement for petroleum refineries to analyze and implement inherently safer design strategies to reduce the risk of serious accidental releases.
  • There were issues with PES’s mechanical integrity program.
  • There were issues with PES’s verification of safety of equipment when new safety information is discovered and published in Recognized and Generally Accepted Good Engineering Practices (RAGAGEP).

Failed Safeguards or Barrier Breakdowns

  • The control system communication to the water pumps had failed at 4:02:06 a.m. (time of ignition).
  • A backup power system in the unit, the uninterruptible power supply (UPS), also failed nine seconds later, at 4:02:15.
  • The water pumps that fed the elevated HF mitigation water cannons did not turn on when the control room operator tried to remotely activate them.
  • The water spray HF mitigation system could not be remotely activated.
  • There were no emergency isolation valves downstream of the pumps, between the pumps and columns T-6 and T-7.
  • The large hydrocarbon sources downstream of the failed elbow could not be remotely or automatically isolated.
  • There was not a CML on the elbow that failed.

Recommendations

  1. 2019-04-I-PA-R1 — Recipient: U.S. Environmental Protection Agency — Status: Open – Acceptable Response or Alternate Response — Develop a program that prioritizes and emphasizes inspections of refinery HF alkylation units, for example under EPA’s National Compliance Initiative called Reducing Risks of Accidental Releases at Industrial and Chemical Facilities. As part of this program, verify that HF alkylation units are complying with API RP 751 Safe Operation of Hydrofluoric Acid Alkylation Units, including but not limited to the implementation of a special emphasis inspection program to inspect all individual carbon steel piping components and welds to identify areas of accelerated corrosion; the protection of safety-critical safeguards and associated control system components, including but not limited to wiring and cabling for control systems and primary and backup power supplies, from fire and explosion hazards including radiant heat and flying projectiles; and the installation of remotely-operated emergency isolation valves on the inlet(s) and outlet(s) of all hydrofluoric acid containing vessels, and hydrocarbon containing vessels meeting defined threshold quantities.
  2. 2019-04-I-PA-R2 — Recipient: U.S. Environmental Protection Agency — Status: Closed – Acceptable Action — Revise 40 C.F.R. Part 68 (EPA Risk Management Plan) to require new and existing petroleum refineries with HF alkylation units to conduct a safer technology and alternatives analysis (STAA) and to evaluate the practicability of any inherently safer technology (IST) identified. Require that these evaluations are performed every 5 years as a part of an initial PHA as well as PHA revalidations.
  3. 2019-04-I-PA-R3 — Recipient: Environmental Protection Agency (EPA) — Status: Closed – Reconsidered/Superseded — Per the requirements in EPA Rule Procedures for Prioritization of Chemicals for Risk Evaluation Under the Toxic Substances Control Act, initiate prioritization to evaluate whether hydrofluoric acid is a High-Priority Substance for risk evaluation. If it is determined to be a High-Priority Substance, conduct a risk evaluation of hydrofluoric acid to determine whether it presents an unreasonable risk of injury to health or the environment. If it is determined to present an unreasonable risk of injury to health or the environment, apply requirements to hydrofluoric acid to the extent necessary to eliminate or significantly mitigate the risk, for example by using a methodology such as the hierarchy of controls.
  4. 2019-04-I-PA-R4 — Recipient: American Petroleum Institute — Status: Open - Awaiting Response or Evaluation/Approval of Response — Update API RP 751 Safe Operation of Hydrofluoric Acid Alkylation Units to require the following: a. Protection of critical safeguards and associated control system components, including but not limited to wiring and cabling for control systems and primary and backup power supplies, from fire and explosion hazards, including radiant heat and flying projectiles; and b. Installation of remotely-operated emergency isolation valves on the inlet(s) and outlet(s) of all hydrofluoric acid containing vessels, and hydrocarbon containing vessels meeting defined threshold quantities.
  5. 2019-04-I-PA-R5 — Recipient: American Society for Testing and Materials (ASTM) International — Status: Closed – Reconsidered/Superseded — Revise ASTM A234 to incorporate supplementary requirements for piping used in HF service, as defined in HF supplementary requirements S9.1 through S9.7 in ASTM A106 version 19a.

Key Engineering Lessons

  • HF alkylation unit piping components with elevated nickel and copper content can corrode faster than adjacent components and require inspection of all carbon steel piping circuit components, not only designated condition monitoring locations.
  • Condition monitoring locations must be placed so that susceptible components such as elbows are actually monitored for wall loss.
  • Protection of safety-critical control system components and primary/backup power supplies from fire and explosion hazards is necessary for active safeguards to remain available during an incident.
  • Remotely operated emergency isolation valves are needed to isolate large hydrocarbon-containing vessels and large inventories of HF when a release occurs.
  • The ability to remotely activate HF mitigation water cannons can be lost if control system communication and backup power are damaged during the event.

Source Notes

  • Primary incident facts, causes, consequences, and recommendations were taken from the final report (source_priority 1), which overrides lower-priority extracts where conflicts existed.
  • Appendix C was used to refine the rupture location and metallurgical findings for the failed elbow.
  • Recommendation status change summaries were used to capture current recommendation statuses for R1 through R5.
  • Supporting documents were used only to supplement timeline and process-context details that were explicitly stated.

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