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Corrosion, Low Inhibitors Ruptured Pipe

Friday, February 15, 2013

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Insufficient corrosion inhibitors and severe corrosion caused a pipe rupture that triggered a massive explosion and blaze last year at Chevron's refinery in Richmond, CA, investigators have concluded.

Those are among the findings of a final technical report released Wednesday (Feb. 13) by the U.S. Chemical Safety and Hazard Investigation Board (CSB) and Cal/OSHA into the Aug. 6, 2012, pipe rupture and fire at California's third-largest refinery.

Prepared by Anamet Inc., the report concluded that the eight-inch steel pipe installed in 1976 ruptured because of severe sulfidation corrosion. Tested pipe samples showed a very low concentration of corrosion-inhibiting silicon, the report said.

Anamet Inc.

"The report ... provides a solid, technical basis for the firm conclusion that the pipe corroded over time from sulfidation corrosion," said Rafael Moure-Eraso, CSB Chairperson.

"The report ... provides a solid, technical basis for the firm conclusion that the pipe corroded over time from sulfidation corrosion," said Rafael Moure-Eraso, CSB Chairperson.

"We hope this report receives widespread attention throughout the petrochemical industry as a precaution to all refiners to carefully examine potential corrosion mechanisms and use the safest possible materials of construction to avoid failures.

"Refineries and other plants must incorporate strong mechanical integrity and inherently safer strategies in their process safety management programs," Moure-Eraso said.

Record Fine After Blast

After the series of explosions and massive fire at Chevron's Richmond refinery in August 2012, Cal/OSHA fined the company $963,200—a record for the state agency.

After investigating the fire and Chevron's leak repair procedures, Cal/OSHA inspectors concluded that Chevron "did not follow the recommendations of its own inspectors and metallurgical scientists to replace the corroded pipe that ultimately ruptured and caused the fire."

Chevron later admitted that it had not inspected the pipe section that later ruptured during scheduled maintenance in 2011.

Reports also emerged that refinery employees had previously complained about unchecked corrosion after an earlier fire at the facility in October 2011. Workers told regulators that Chevron was ignoring corrosion at the facility.

Report Conclusions

The report, which examined and analyzed dozens of pipe samples, was a cooperative effort between the CSB, California's Occupational Safety and Health Administration, Chevron, and the United Steelworkers.

Toni Hanna / richmondconfidential.org

Cal/OSHA fined Chevron almost $1 million after the explosion, which was a record for the state agency.

Based on the submitted samples and evidence gathered, Anamet's report concluded the following.

  • Rupture of the eight-inch four-sidecut pipe section resulted from wall thinning caused by sulfidation corrosion.
  • Post-rupture corrosion destroyed fracture morphology that could have indicated the rupture initiation site. However, the rupture probably originated in the thinnest region and initially followed a longitudinal path driven by the hoop stress. Consequently, an area of likely rupture was identified.
  • The wall thickness of the ruptured section was less than any of the other eight-inch four-sidecut pipe sections evaluated.
  • Chemical analysis showed the silicon concentration of the ruptured section was 0.01-wt%. Silicon in carbon steel inhibits sulfidation when the silicone concentration is above 0.10-wt%; below this level, corrosion can be significantly faster.
  • Chemical analysis showed half of the specimens from unique sections of the eight-inch four-sidecut, 12-inch four-sidecut, and 12-inch samples from 2011 w a siliithcon concentration of less than 0.10-wt%.
  • Deformation of a small region of the eight-inch four-sidecut rupture edge was consistent with mechanical force applied from the outside surface of the pipe, possibly from a fire pike, or other pointed object. This deformed region was located within the area of likely rupture initiation.

The report, which was funded by the CSB, concludes, "The reported service conditions of the #4 Crude Unit four-sidecut piping, the composition of the carbon steel, presence of thick sulfide scale on the inside surfaces of the pipe, and generally uniform wall thinning indicate that sulfidation corrosion was the cause of the eight-inch four-sidecut rupture."

Pipe 'Should Have Been Replaced'

Cal/OSHA Chief Ellen Widess said, "This report confirms what Chevron already knew—that the pipe was severely corroded and should have been replaced—but failed to act on before the August fire. This fire was included among multiple serious and willful serious citations that Cal/OSHA recently issued to Chevron.

"Chevron's own metallurgists and pipe inspectors reached the same conclusion and recommended as far back as 2002 that Chevron take action to protect its workers, the community and the environment by replacing the pipe that finally ruptured in 2012," Widess said.

Anamet Inc.

A fragment of the ruptured pipe and two fire pikes were collected post incident. The report found that a fire pike may have caused a puncture in the pipe.

Chevron Responds

In responding to CSB's report Wednesday, Chevron said the finding of low silicon content in the failed carbon steel pipe was consistent with the company's own preliminary observation in September 2012.

"Chevron U.S.A is inspecting every pipe component in the crude unit susceptible to sulfidation corrosion. Any component found to be unsuitable for service will be replaced for restarting the unit," the response said.

It continued: "While we do not agree with some of the characterizations in today's Chemical Safety Board news release, we are committed to discussing the findings from our investigation and our corrective actions with the investigating agencies prior to release of the report and restart of the crude unit."

Located in Hayward, CA, Anamet Inc. provides materials engineering analysis and laboratory testing and performs failure analysis and forensic engineering to determine the root cause of mechanical, metallurgical, or corrosion failures.

   

Tagged categories: Corrosion; Explosions; OSHA; Pipeline; U.S. Chemical Safety Board

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