Pipe samples from Chevron USA Inc.’s El Segundo, Calif., refinery show similar sulfidation corrosion to samples from the company’s Richmond, Calif., plant where a crude oil unit caught fire on Aug. 6, 2012, a report showed.
The US Chemical Safety Board and California Division of Occupational Safety and Health (Cal/OSHA) jointly issued the report.
The pipe sample from the 285,000 b/d El Segundo refinery west of Los Angeles, had lost up to 60% of its wall thickness, from 0.322 inches to 0.12 inches in the thinnest part, showed the report by Anamet Inc., a Hayward, Calif., independent materials engineering and testing laboratory.
After the August fire at the 250,000 b/d Richmond plant, CSB said on Apr. 19, Chevron voluntarily inspected and upgraded corresponding sections of piping from El Segundo, which has a nearly identical crude unit. The tests compared sections of pipe from sidecuts in the two crude units, the federal agency said.
CSB and Cal/OSHA investigations determined that sulfidation corrosion and severe pipe thinning made the Richmond plant’s crude distillation tower piping fail. No release or incident occurred at El Segundo, and Chevron has since replaced the corroded piping with an upgraded metallurgy that is more resistant to sulfidation corrosion, CSB said.
The removed pipe from El Segundo was secured and preserved for testing under an order from Cal/OSHA process safety inspectors, who recognized the similarity between the two crude units and sought to determine whether similar corrosion had occurred at El Segundo to what was observed at Richmond. The pipe later was transferred to Anamet’s laboratory in Hayward under a joint testing protocol.
Sulfidation corrosion found
“Sulfidation corrosion had affected the El Segundo samples to a similar extent as the Richmond samples had been affected,” the report concluded. “The obvious difference between the two sidecut lines was that Richmond suffered more extensive corrosion in one component that resulted in rupture.”
It said silicon content, which helps fight corrosion, was low in both cases. Older carbon steel piping, which is common in refineries, can have widely varying levels of protective silicon, a trace constituent that is hard to measure under field conditions, CSB said.
Chevron USA did not apply inherently safer design principles and upgrade piping at the Richmond refinery’s crude processing unit over 10 years, leading to extreme corrosion which made the pipe rupture and release a vapor cloud that ultimately caught fire on Aug. 6, CSB said in a draft report of its investigation on Apr. 15 (OGJ Online, Apr. 15, 2013).
Chevron said on Apr. 12 that its investigation of the incident determined sulfidation corrosion accelerated by low-silicon content made the 5-ft carbon steel component rupture at Richmond in August.
Enhanced component inspection similar to what Chevron USA is implementing across its refining network would likely have alerted operators at the Richmond plant that there was a potential problem, the company continued. It said it would implement measures to address underlying issues its investigation identified, and strengthen process safety, mechanical integrity, and management oversight.
CSB held a public meeting about its draft report at the Richmond Civic Center on Apr. 19. The agency also postponed an Apr. 24 public meeting in Washington on operator fatigue and other open safety recommendations because it deployed a significant number of employees to investigate an Apr. 17 fertilizer plant explosion west of Waco, Tex.
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