The U.S. Chemical Safety and Hazard Investigation Board and the California Division of Occupational Safety and Health released a technical evaluation report on piping samples taken from the Chevron Refinery in Richmond, Calif., where a hydrocarbon release and massive fire occurred on Aug. 6, 2012.
Cal/OSHA participated in technical evaluation as part of its enforcement investigation.
The report was issued late Wednesday. It was prepared by Anamet Inc., a metallurgical laboratory in Hayward, Calif., concludes that the 8-inch steel pipe from a section installed in 1976 ruptured due to severe sulfidation corrosion, and that tested pipe samples showed a very low concentration of corrosion-inhibiting silicon.
“This reports 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,” Cal/OSHA Chief Ellen Widess said in a statement. “This failure to act was included among the multiple Serious and Willful Serious citations 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.”
California workplace safety officials have fined Chevron Corp. $1 million in connection with a fire last year at the company’s San Francisco Bay area refinery that sent a cloud of gas and black smoke over residential areas. The company has paid $10 million in claims stemming from the fire at its 245,000-barrels-per-day refinery.
CSB determined that 19 Chevron employees were engulfed in a vapor cloud formed by the hydrocarbon release, while 19 employees escaped before the fire started and one employee escaped without injury after the fire ensued. The incident resulted in six minor injuries. Production at the crude unit has been suspended since the accident. More than 15,000 residents in the surrounding area sought treatment at area medical facilities as a result of the release and fire.
The report cites wall thinning due to sulfidation corrosion as the cause of the piping failure. In crude oil distillation, the report notes, naturally occurring sulfur and sulfur compounds are available to react with steel components, particularly plain carbon steels. Corrosion rates vary according to the sulfur content of the oil being processed, temperature, and other factors, including silicon content and other materials in steel pipe.
The report noted that the failed pipe section was subjected to a higher corrosion rate than neighboring components due to low silicon content in the pipe. The report states that “Experience has shown that silicon in carbon steel is known to inhibit sulfidation” when the concentration is above a threshold value. Chemical analysis of the Chevron pipe showed the silicon concentration of the ruptured section to be far below this value, resulting in a significantly higher rate of sulfidation corrosion.
The report also notes the presence of an inward deformation toward the inside surface of the pipe. CSB determined this deformation was likely caused by a fire pike used during the plant’s emergency response.
The incident occurred when a combustible hydrocarbon liquid known as “gas oil” leaked from an 8-inch pipe connected to an atmospheric crude oil distillation column in the refinery’s crude unit. Workers initially noted the leak and were in the process of attempting to diagnose the source of the leak in the still-operating crude unit when the pipe ruptured catastrophically. Due to the high temperature, in excess of 600 degrees Fahrenheit, and physical properties of the material in the equipment, the gas-oil immediately formed a large hydrocarbon vapor cloud, the report shows.
The CSB investigation to determine the root causes of the incident is ongoing. CSB will release a report detailing its findings and recommendations to key stakeholders later this year. Cal/OSHA has already issued 25 citations and civil penalties of $963,000. Chevron has announced it will appeal these citations.
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