Corrosion Failure — HF Alkylation Unit; Catastrophic Vessel Rupture
Philadelphia Energy Solutions Refinery HF Alkylation Fire and Explosions
Philadelphia Energy Solutions (PES)
📍 Philadelphia, PA
Incident: June 21, 2019  •  CSB Report: October 11, 2022
0
Fatalities
Hydrofluoric Acid (HF, 5,000+ lbs) + Hydrocarbons
Chemical Involved
5
CSB Recommendations
📋 Incident Summary

On June 21, 2019, a fire and series of explosions at the Philadelphia Energy Solutions (PES) refinery — the largest on the U.S. East Coast — injured five workers and one firefighter and caused approximately $750 million in damage. A corroded carbon steel elbow in the HF alkylation unit failed, releasing hydrocarbons and HF acid. The fire escalated to a catastrophic failure of the V-1 Treater Feed Surge Drum, which ruptured in a third explosion at 4:22 AM, launching an estimated 38,000-pound fragment across the Schuylkill River.

The CSB found the failed elbow had corroded to near-zero wall thickness due to high-velocity HF acid service and the facility's MI program had not adequately monitored corrosion at that location. The incident led PES to declare bankruptcy and permanently close the refinery.

The October 2022 CSB report issued 5 recommendations to EPA, API, and ASTM — focused on mandatory remotely operated emergency isolation valves (ROEIVs) for HF alkylation units and regulatory improvements for HF processes under RMP.

🔎 Key Findings
Finding 01
Corroded Elbow Failed Near-Zero Wall Thickness
A carbon steel pipe elbow corroded to near-zero remaining wall thickness due to high-velocity HF acid service — the MI inspection program did not adequately detect or respond to the advancing corrosion.
Finding 02
HF Alkylation Unit Had No ROEIVs
The unit did not have remotely operated emergency isolation valves (ROEIVs) to stop HF and hydrocarbon flow from a safe distance when the elbow failed — safe isolation was impossible.
Finding 03
V-1 Vessel Ruptured — 38,000-lb Fragment Launched Across River
As fire escalated, the V-1 Treater Feed Surge Drum failed catastrophically, launching an estimated 38,000-pound fragment across the Schuylkill River — one of the largest vessel fragments ever documented in a U.S. refinery incident.
Finding 04
MI Program Did Not Flag Advancing Corrosion
Inspection records did not reflect the severity of corrosion in the HF acid circuit or trigger corrective action — a systemic failure to monitor a known, high-consequence corrosion mechanism.
Finding 05
PES Declared Bankruptcy and Closed Permanently
The ~$750M damage led PES to declare bankruptcy and permanently close the largest refinery on the U.S. East Coast — illustrating the existential business risk of catastrophic process safety events.
🔍 Root Causes
1
MI Failure — Corrosion Not Detected
The facility's MI program did not include inspection methods, frequencies, or coverage adequate to detect accelerated corrosion in the HF acid alkylation circuit — a systemic failure that allowed the elbow to reach failure condition undetected.
2
No ROEIVs on HF Supply Lines
PES had not installed ROEIVs on HF supply and distribution lines despite known HF aerosol formation hazards and longstanding CSB recommendations to the refining industry.
3
RMP/PSM Regulations Did Not Require ROEIVs
OSHA PSM and EPA RMP regulations did not explicitly require ROEIVs for HF alkylation units — a regulatory gap allowing refineries to operate large HF inventories without engineered emergency isolation.
☑ CSB Recommendations
→ EPA (3 recs, 1 closed / 2 open or superseded)
Amend the RMP rule to require remotely operated emergency isolation valves (ROEIVs) for all HF alkylation units as a mandatory engineering control, with defined performance standards and implementation timelines.
→ EPA
Require HF alkylation facilities to conduct consequence analyses for catastrophic HF aerosol release scenarios and document community notification and evacuation protocols in their RMP Emergency Response Program.
→ EPA
Strengthen RMP accident prevention program requirements for HF alkylation facilities, including specific corrosion monitoring requirements for HF acid circuits.
→ API (1 rec, open)
Update API Recommended Practice 751 to require remotely operated emergency isolation valves as a mandatory safeguard and to provide updated corrosion monitoring guidance for HF acid service piping.
→ ASTM (1 rec, closed/superseded)
Update ASTM corrosion testing standards applicable to HF acid service materials to ensure they reflect actual service conditions and provide adequate guidance for corrosion rate prediction in HF alkylation piping circuits.
💡 Lessons Learned
Mechanical integrity programs must cover all high-consequence piping — not just major vessels. A small corroded elbow in HF acid service can initiate a catastrophic sequence when it fails.
Remotely operated emergency isolation valves (ROEIVs) are critical safeguards for HF alkylation units. When a release occurs, stopping flow from a safe distance can be the difference between a contained incident and a catastrophic HF cloud.
Corrosion in HF acid service is aggressive and location-specific. MI programs must use inspection methods and frequencies that can detect high corrosion rates before failure — not just inspect accessible locations on a schedule.
HF alkylation units contain thousands of pounds of one of the most hazardous materials regulated by PSM and RMP. Engineering controls enabling rapid emergency isolation are not optional enhancements — they are essential safeguards.
The bankruptcy and permanent closure of PES illustrates that catastrophic process safety events carry existential business risk — not just safety and environmental consequences.
PSI: Process Safety InformationMI: Mechanical IntegrityPHA: Process Hazard AnalysisEAP: Emergency Planning & Response
🔨 Safety Meeting Toolbox Talk
►Does your MI program specifically address high-corrosion-rate service conditions, including acid service piping? When were those locations last inspected?
►Are remotely operated emergency isolation valves installed on your most hazardous process streams? If there were a release right now, could you stop flow from a safe location?
►How does your facility track inspection results for piping — and what triggers an immediate corrective action versus a scheduled repair?
►What is the most hazardous chemical release scenario at your facility from a community impact standpoint? Does your emergency response plan specifically address it?
►If a small elbow or fitting in a high-hazard service failed today, would your operators know where the isolation valves are and whether they could be safely operated?
Immediate Action Items
✓Identify the highest-consequence piping circuits at your facility (acid service, high-temperature, high-pressure) and verify MI inspection coverage, methods, and frequency are adequate for those locations.
✓Walk down your most hazardous process unit and identify manual isolation valves that could not be safely operated during a release due to their location.
✓Pull MI inspection records for the highest-risk piping circuits and verify that corrosion trending and remaining-life calculations are being performed and reviewed by a qualified inspector.
✓Review your emergency response plan to confirm it specifically addresses your highest-consequence release scenario, including isolation steps, community notification, and evacuation triggers.
✓Confirm that your PSI includes current P&IDs accurately reflecting process piping configuration, including all recent modifications.
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 4 PSM elements (PSI · MI · PHA · EAP). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Process Safety Information (PSI)
Accurate, complete Process Safety Information is the foundation every other PSM element depends on. When PSI is missing or wrong — chemistry data, equipment specs, P&IDs — the entire hazard analysis is built on a flawed base.
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Mechanical Integrity (MI)
Equipment must be designed, inspected, and maintained to operate safely in its intended service. Mechanical integrity failures — degraded equipment, missed inspections, deferred repairs — contributed to loss of containment here.
Supporting documents in our library →
Process Hazard Analysis (PHA)
A structured PHA or HAZOP study exists to identify exactly these scenarios before they occur. When PHA is absent, superficial, or overdue for revalidation, hazards operate unseen until they kill someone.
Supporting documents in our library →
Emergency Planning & Response
When process safety barriers fail, emergency response capability determines whether the outcome is controlled or catastrophic. Gaps in emergency preparedness amplified the consequences here.
Supporting documents in our library →
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