Last week, the U.S. Chemical Safety & Hazard Investigation Board released its draft report about a 2010 fire at a Tesoro refinery in Anacortes, Wash., that killed seven workers. The fire occurred when a naphtha heat exchanger ruptured, the report says. The cause of the rupture was high temperature hydrogen attack, which occurs when hydrogen atoms diffuse into carbon steel and react with the carbon to form methane. The methane accumulates in the steel and causes stress and fissures. CSB found that curves established by the American Petroleum Institute to predict high temperature hydrogen attack are inaccurate. “CSB has learned of at least eight recent refinery incidents where HTHA reportedly occurred below the carbon steel Nelson curve,” the report says.
Here’s CSB’s video about the incident:
The CSB found several indications of process safety culture deficiencies at the Tesoro Anacortes Refinery. Refinery management had normalized the occurrences of hazardous conditions, including frequent leaks from the [naphtha hydrotreater unit] heat exchangers, by using steam to mitigate leaks, ineffectively correcting heat exchanger design issues, commonly requiring additional operators during [naphtha hydrotreater unit] heat exchanger startups, and exceeding the staffing levels that procedures specified.
The refinery process safety culture required proof of danger rather than proof of effective safety implementation. For years, technical experts used design data to evaluate the B and E heat exchangers for HTHA susceptibility. Data for actual operating conditions were not readily available, and these technical experts were not required to prove safety effectiveness in reaching their conclusion that the B and E heat exchangers were not susceptible to HTHA damage.
CSB noted several similarities between the Tesoro fire and a Chevron refinery fire in Richmond, Calif., in 2012:
- The Chevron “incident was also the result of a metallurgical failure caused by a well-known damage mechanism called sulfidation corrosion, and Chevron process safety programs failed to identify the hazard before the major incident that endangered the lives of 19 Chevron employees.”
- “Mechanical integrity programs at both Tesoro and Chevron emphasized inspection strategies rather than the use of inherently safer design to control the damage mechanisms that ultimately caused the major process safety incidents.”
- “Rather than performing rigorous analyses of damage mechanisms during the PHA process, both companies simply cited non-specific, judgment-based qualitative safeguards to reduce the risk of damage mechanisms.”
One of the recommendations CSB makes in its Tesoro report is that Washington state implement a “safety case” approach to regulation, in which companies develop their own process safety requirements that are closely overseen by state regulators. The agency made the same recommendation to California in its Chevron report, but that report fell to a divided vote by CSB board members, with board members Beth Rosenberg and Mark Griffon wanting CSB to study regulatory options further. An expected vote on the Tesoro report last week was delayed. What happens from here is an open question. Given criticism of CSB that the agency is taking too long already to complete its investigations, holding reports for further study seems untenable. The federal budget passed last month allotted CSB “$11 million for fiscal 2014, slightly less than previous years and below the Administration’s request of $11.5 million.”
Feb. 5, 2014: Title changed to reflect the fact that although I saw the heat exchangers as a bundle of tubes inside a larger tube, CSB tells me that engineers view the outer structure as a shell, not a tube. In any case, weakened steel from high temperature hydrogen attack was still the problem.