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Sonat Exploration Co. Catastrophic Vessel Overpressurization

Overview

At approximately 6:15 p.m. on March 4, 1998, a catastrophic vessel failure and fire occurred at the Temple 22-1 Common Point Separation Facility near Pitkin, Louisiana. Four workers who were near the vessel were killed, and the facility sustained significant damage. The vessel lacked a pressure relief system and ruptured due to overpressurization during start-up, releasing flammable material which ignited.

Incident Snapshot

Field Value
Facility / Company Sonat Exploration Co.
Location Pitkin, LA
Incident Date 03/04/1998
Investigation Status The final report on this investigation was approved on September 21, 2000.
Accident Type Oil and Refining - Fire and Explosion Investigation
Final Report Release Date 09/21/2000

What Happened

  • On the day of the incident, one of the two separation trains was to be put in operation and production was to be initiated from the Temple 24-1 well.
  • Facility supervisors intended to purge the pipeline by opening the 24-1 well and using well fluid to displace air out of the pipeline and through a storage tank roof hatch, located at the end of the production train.
  • The purging process was initiated and then conducted for approximately 60 minutes.
  • At around 6:00 p.m., the pressure immediately downstream of valve 22, the 24-1 choke, was approximately 800 psig as indicated by pressure gauge 27.
  • At about 6:10 p.m., the construction supervisor obtained a final oxygen reading of less than 3%.
  • At approximately 6:15 p.m., the Bulk Train third-stage separator experienced a catastrophic failure.
  • The surviving contract operator activated an emergency shutdown device, which automatically shut down the 22-1 well.
  • Emergency personnel eventually extinguished all fires by 9:47 p.m.

Facility and Process Context

  • The facility housed two petroleum separation trains and consisted of separation equipment, piping, storage vessels, and a gas distribution system.
  • The separation trains were designed to produce crude oil and natural gas from well fluid derived from two nearby wells.
  • At the time of the incident, the facility was configured to process the output from two wells known as Temple 22-1 and Temple 24-1.
  • Sonat constructed two independent separation trains, identified as the Bulk Train and the Test Train.
  • Each separation train comprised three separators connected in series.
  • The first two separators were designed for three-phase (gas/oil/water) separation, while the third-stage separator was designed for two-phase (gas/oil) separation.
  • The third-stage separator had an MAWP of 0 psig (atmospheric pressure) and would have operated around this pressure during normal operation.
  • The facility was designed for automated operation with periodic monitoring by operators.

Consequences

  • Fatalities: 4 workers were killed; four workers who were near the vessel were killed; all four operators who were near the separator at the time of the failure were killed at once.
  • Injuries: Two other workers who were present at the facility at the time of the incident both survived without injury. The operator stationed near the header and the construction supervisor survived without serious injury.
  • Environmental Release: The vessel ruptured due to overpressurization, releasing flammable material which then ignited. Gas from the ruptured vessel produced a large fireball, which damaged nearby piping and released and ignited additional flammable materials. The two-mile stretch of pipeline contained a significant volume of pressurized natural gas that continued to leak from the damaged Bulk Train piping.
  • Facility Damage: The facility sustained significant damage. The separator, four personal vehicles, and a backhoe were destroyed, and there was damage to oil and water storage tanks. About $200,000 worth of damage occurred, including the destruction of the third-stage separator, four private vehicles, and a backhoe and damage to the facility storage tanks.
  • Operational Impact: The 24-1 well was shut in following the vessel failure. The gas sales pipeline valve was closed. All fires were extinguished by 9:47 p.m.

Key Findings

Immediate Causes

  • The third-stage separator lacked an inlet valve and therefore could not be isolated from an adjacent bypass line, which at the time of the incident contained high-pressure purge gases.
  • Two outlet block valves on the separator were closed, as were two block valves on the bypass line downstream of the separator. Accordingly the high-pressure purge gases could not be vented and the separator was overpressurized.
  • The third-stage separator was only rated for atmospheric pressure service (0 psig). The purge gas stream to which the separator was exposed had a pressure potentially as high as 800 psig.
  • The separator was not equipped with any pressure-relief devices, and overpressurization caused the separator to fail catastrophically.
  • The vessel was exposed to a pressure significantly in excess of its maximum allowable working pressure, resulting in catastrophic vessel failure.

Contributing Factors

  • The timing of the closure of valves 11 and 13 could not be absolutely determined.
  • The facility was designed and built without effective engineering design reviews or hazard analyses.
  • Workers at the facility were not provided with written operating procedures addressing the alignment of valves during purging operations.
  • Sonat operated third-stage separators that lacked adequate pressure-relief systems at other oil and gas production facilities for over a year prior to the incident.
  • Prior to the incident, Sonat did not have a documented piping and instrumentation diagram (P&ID) for the facility; only after the incident were process diagrams and P&IDs generated and process hazard analyses conducted.
  • Sonat had written safety procedures covering generic subjects such as confined space entry, excavating and trenching, and lock-out/tag-out of equipment. However, there were no written operating procedures for oil and gas production facilities.
  • Sonat did not have an evaluation program for on-the-job training.
  • Formal, process-specific training was not a component of Sonat’s safety program.

Organizational and Systemic Factors

  • Sonat management did not use a formal engineering design review process or require effective hazard analyses in the course of designing and building the facility.
  • Sonat engineering specifications did not ensure that equipment that could potentially be exposed to high-pressure hazards was adequately protected by pressure-relief devices.
  • Sonat management did not provide workers with written operating procedures for the start-up and operation of the facility.
  • Sonat preferred to use oral instructions to train and direct facility operations.
  • Sonat’s personnel training program had three components: on-the-job instruction, monthly internal safety meetings, and external coursework.
  • Contractors were used widely by Sonat for facility construction, start-up, and maintenance, and other functions.
  • Sonat lacked adequate written, process-specific operating procedures and process hazard information.
  • The incident would likely have been prevented if process safety management principles or good engineering practice had been followed more effectively at the facility.

Failed Safeguards or Barrier Breakdowns

  • The third-stage separator lacked an inlet valve.
  • The separator was not equipped with any pressure-relief devices.
  • The facility was designed and built without effective engineering design reviews or hazard analyses.
  • Workers at the facility were not provided with written operating procedures addressing the alignment of valves during purging operations.
  • The third-stage separator was not equipped with a pressure sensor or alarm to indicate overpressurization.
  • Sonat did not have a documented piping and instrumentation diagram (P&ID) for the facility prior to the incident.
  • Sonat did not have an evaluation program for on-the-job training.
  • There were no written operating procedures for oil and gas production facilities.

Recommendations

  1. 1998-002-I-LA-R1 | Recipient: El Paso Production Company (formerly Sonat Exploration Company) | Status: Open | Summary: Institute a formal engineering design review process for all oil and gas production facilities, following good engineering practices and including analyses of process hazards.
  2. 1998-002-I-LA-R2 | Recipient: El Paso Production Company (formerly Sonat Exploration Company) | Status: Open | Summary: Implement a program to ensure that all oil and gas production equipment that is potentially subject to overpressurization is equipped with adequate pressure-relief systems, and audit compliance with the program.
  3. 1998-002-I-LA-R3 | Recipient: El Paso Production Company (formerly Sonat Exploration Company) | Status: Open | Summary: Develop written operating procedures for oil and gas production facilities and implement programs to ensure that all workers, including contract employees, are trained in the use of the procedures. Ensure the procedures address, at a minimum, purging and start-up operations and provide information on process-related hazards.
  4. 1998-002-I-LA-R4 | Recipient: American Petroleum Institute | Status: Open | Summary: Develop and issue recommended practice guidelines governing the safe start-up and operation of oil and gas production facilities. Ensure that the guidelines address, at a minimum, the following: project design review processes, including hazard analyses; written operating procedures; employee and contractor training; and pressure-relief requirements for all equipment exposed to pressure hazards.
  5. 1998-02-I-LA-R5 | Recipient: American Petroleum Institute | Status: Open | Summary: Communicate the findings of this report to your membership.

Key Engineering Lessons

  • Equipment that can be exposed to high-pressure purge gases must be protected by adequate pressure-relief devices.
  • A vessel that cannot be isolated from a bypass line can be overpressurized if valves are misaligned during purging or start-up.
  • Process design reviews and hazard analyses are needed before construction and start-up of oil and gas production facilities.
  • Written operating procedures are needed for purging and start-up operations, including valve alignment.
  • Process-specific drawings and P&IDs are important process hazard information for safe operation and training.

Source Notes

  • Priority 1 final report used to resolve conflicts and establish authoritative findings, recommendations, and terminology.
  • Supporting documents were used only to supplement event sequence and context where consistent with the final report.
  • Some supporting documents contained partially garbled or summary text; conflicting or less specific wording was not used when the final report provided clearer information.

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