The U.S. Chemical Safety Board (CSB), Washington, D.C., states in a published draft report that high-temperature-hydrogen-attack (HTHA) damage to a heat exchanger caused the April 2010 explosion and fire at the Tesoro refinery, Anacortes, Wash., that killed seven workers. The report also notes the company failed to apply inherently safer technology and install damage-resistant materials.
"Seven lives were tragically lost at the Tesoro refinery in 2010," says Dr. Rafael Moure-Eraso, CSB chairperson. "I believe the draft report does an outstanding job of tracing this complex accident to its roots: a deficient refinery safety culture, weak industry standards for safeguarding equipment, and a regulatory system that too often emphasizes activities rather than outcomes. The report is a clarion call for refinery safety reform."
Using sophisticated computer models, the investigation found the industry-wide method used to predict the risk of HTHA damage to be inaccurate, with equipment failures occurring under conditions deemed to be safe from HTHA. It cited deficiencies in the company's safety culture that led to a "complacent" attitude toward flammable leaks and occasional fires. Investigators determined that during the unit startup, Tesoro did not correct the history of hazardous conditions or limit the number of people involved in the non-routine startup of the heat exchangers. Instead, because reoccurring leaks and the need to manually open a series of long-winded valves requiring more than 100 turns by hand to fully open, a supervisor requested five additional workers to help. All seven lost their lives as a result of the blast.
Moure-Eraso adds, "The accident at Tesoro could have been prevented had the company applied inherent safety principles and used HTHA-resistant construction materials to prevent the heat exchanger cracking. This accident is very similar to the one that occurred at the Chevron refinery in Richmond, Calif. in August 2012, where corrosion of piping went undetected for decades until it ruptured, endangering the lives of 19 workers caught in a vapor cloud and sending 15,000 community members to the hospital. Companies must do a better job of preventing refinery accidents, which occur all too frequently."
The draft report notes that recommended practices of the American Petroleum Institute (API) are written "permissively" with no minimum requirements to prevent HTHA failures. For example, API Recommended Practice 941 — Steels for Hydrogen Service at Elevated Temperatures and Pressures… — uses the term "should" 27 times and "shall" only once. It also doesn't require users to verify actual operating conditions in establishing operation limits of the equipment, or to confirm that the materials of construction will prevent the damage. An inspection strategy that relied on design operating conditions rather than verifying actual operating parameters contributed to the accident.
The investigation found Tesoro, like others in the industry, used published data from the API called Nelson curves, to predict the susceptibility of the heat exchangers to HTHA damage. The CSB found these curves unreliable because they use historical data concerning HTHA that may not sufficiently reflect actual operating conditions. For example, a CSB computer reconstruction of the process conditions in the exchangers determined that the portion of the carbon steel exchanger that failed likely operated below the applicable Nelson curve — indicating it was "safe."
The CSB determined that inspections for such damage are unreliable because the microscopic cracks can be localized and difficult to identify. The report concludes, "Inherently safer design is a better approach to prevent HTHA." It notes that API has identified high-chromium steels that are highly resistant; these were not installed by Tesoro. The CSB has called for the adoption of inherently safer technology, design and equipment in other reports, notably the one on the Chevron refinery fire.
The draft report — subject to a future vote by the CSB — makes numerous safety recommendations to Washington's legislature and governor, to its regulatory agency, Tesoro, and the API. These include recommending the state establish a more-rigorous regulatory model, possibly based on the safety case regime; revise the state's process safety management regulations to ensure prevention of catastrophic releases; and perform a safety verification audit at all refineries in the state.
The CSB also released a computer animation that recreates the explosion and fire at the refinery. The five-minute animation illustrates the process of HTHA and can be seen here: http://goo.gl/FzLISG.
The draft report is available at www.csb.gov for public comment until March 16, 2014. Comments should be sent to firstname.lastname@example.org. All comments received will be reviewed and published on the CSB website.
Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at email@example.com