CSB Investigation — Fire & Explosion
Valero McKee Refinery Propane Fire
Valero Energy Corporation
📍 Sunray, TX
Incident Date: February 16, 2007  |  CSB Report Released: February 2008
0
Fatalities
4
Injuries
5
CSB Recommendations
$50M+
Estimated Damage
📋 Incident Summary

On February 16, 2007, a fire and explosion destroyed the propane deasphalting (PDA) unit at the Valero McKee Refinery in Sunray, Texas, injuring four workers and causing more than $50 million in damage. The PDA unit was a critical process unit handling large volumes of liquid propane under high pressure.

The root cause was the freezing of water inside a "dead-leg" — a stagnant, isolated section of 10-inch liquid propane piping that was not part of active flow during normal operations. During the cold winter days preceding the incident, water accumulated in the dead-leg froze, expanded, and cracked the pipe. When temperatures rose, the cracked propane line released a large liquid propane vapor cloud that found an ignition source and detonated, destroying the unit.

The CSB found that the Valero McKee refinery had no systematic program to identify dead-legs in its piping systems, assess their freeze potential, or provide targeted freeze protection measures. Dead-legs in hydrocarbon service are a well-known integrity risk in cold climates, yet no PSM-quality mechanical integrity provisions addressed this hazard at this refinery.

🔎 Key Findings
Finding 1
Dead-Leg Freeze Cracked Propane Line
Water trapped in an isolated dead-leg section of 10-inch liquid propane piping froze, expanded, and cracked the pipe. This cracked pipe was the release point for the large propane vapor cloud.
Finding 2
No Dead-Leg Identification Program
The refinery had no systematic program to identify all dead-legs in its piping systems, catalog their characteristics, assess freeze risk, or apply appropriate winterization measures.
Finding 3
Inadequate Freeze Protection Program
The freeze protection program did not specifically address dead-legs in high-pressure hydrocarbon service. General freeze protection measures did not adequately cover isolated, stagnant piping sections.
Finding 4
Large Propane Vapor Cloud Ignited
The cracked propane line released a substantial liquid propane cloud. Vapor cloud ignition destroyed the PDA unit and injured four workers in the vicinity.
Finding 5
$50M+ Loss from Preventable Freeze Crack
The propane deasphalting unit was permanently destroyed, resulting in long-term production impact — a consequence entirely preventable by a dead-leg management program.
Finding 6
Dead-Legs as Known Mechanical Integrity Hazard
Dead-legs in liquid service are a well-documented piping integrity hazard. Freeze cracking, corrosion, and stress accumulation in stagnant sections are established failure mechanisms requiring active MI management.
🔍 Root Causes
1
Failure to Identify and Manage Dead-Legs
The refinery had not identified, cataloged, or managed dead-legs in its piping systems as a mechanical integrity concern, leaving this known failure mechanism unaddressed.
2
Inadequate Freeze Protection for Isolated Piping
The freeze protection program did not specifically address isolated dead-leg sections in high-pressure hydrocarbon service.
3
Absent Winter Operating Procedures for Dead-Legs
No winter operating procedures required monitoring or draining of dead-leg sections prior to freezing weather conditions.
4
MI Program Gap for Dead-Leg Piping
The mechanical integrity program did not comprehensively cover dead-leg piping sections in high-hazard services — focusing primarily on major equipment and active flow lines.
☑ CSB Recommendations
→ Valero
Implement a comprehensive dead-leg identification and management program covering all process units, including cataloging, freeze risk assessment, and targeted protective measures.
→ Valero
Revise the winter freeze protection program to include specific inspection and monitoring requirements for all dead-legs in liquid hydrocarbon and water-containing piping services.
→ API
Update API 570 guidance on dead-leg identification and integrity management to include specific requirements for freeze risk assessment in cold-climate operations.
→ OSHA
Issue a safety communication reminding PSM-covered facilities of the MI requirement to identify and manage all types of piping integrity hazards, including dead-legs.
→ Valero
Develop winter operating procedures for all process units requiring documented inspection and verification of dead-leg conditions before onset of predicted freezing temperatures.
💡 Lessons Learned
⚠ Dead-legs — isolated, stagnant pipe sections — are a well-documented mechanical integrity hazard. Water trapped in a dead-leg can freeze, crack the pipe, and release its process contents without warning.
⚠ Freeze protection programs must specifically address dead-legs. General pipe tracing and insulation programs may not address isolated sections that fall outside active flow systems.
⚠ A dead-leg identification and cataloging program is a basic mechanical integrity requirement for any facility in a climate where freezing temperatures occur. If you have not identified your dead-legs, you cannot protect them.
⚠ Small bore and stagnant piping sections are frequently overlooked in MI programs that focus on major equipment and main flow lines. These sections deserve the same rigor as any other high-hazard piping.
⚠ The cost of a dead-leg management program is tiny compared to the cost of a propane unit destroyed by a preventable freeze crack.
PSM Elements: MI · SOP · PSI · PHA
🔨 Safety Meeting Toolbox Talk
Topic: Dead-Leg Freeze Management & Cold-Climate Mechanical Integrity
💬Has our facility conducted a systematic dead-leg survey to identify all isolated, stagnant piping sections in hydrocarbon and water-containing services?
💬Does our freeze protection program specifically address dead-legs — not just active flow piping — with targeted inspection, tracing, insulation, or draining requirements?
💬Do we have written winter operating procedures that require inspection or draining of dead-legs before predicted freezing temperatures arrive?
💬Are dead-legs in our facility listed in the mechanical integrity inspection database with documented inspection history and freeze risk assessment?
💬Have we reviewed our P&IDs specifically looking for isolated branches, blanked stubs, and analyzer connections that may qualify as dead-legs in freeze-susceptible service?
✎ Team Action Items
✓Review piping P&IDs for your unit and identify any isolated branches, blanked connections, or sample points that qualify as dead-legs in liquid or aqueous service
✓Check whether dead-legs are included in your unit mechanical integrity inspection program — if not, flag this as a gap requiring a dead-leg survey
✓Verify that your freeze protection program covers isolated and stagnant piping sections, not just active flow lines
✓Before the next cold weather season, confirm winterization procedures include specific inspection or drainage of dead-legs in hydrocarbon services
🔗 PSM Failures Behind This Incident

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

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.
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Operating Procedures (SOPs)
Operators cannot reliably hold safe operating limits without clear, current, enforced procedures. Deviation from acceptable operating conditions — a root cause here — is a direct consequence of SOP failure.
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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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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.
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