RICHMOND -- A metallurgical laboratory report released Wednesday confirms earlier conclusions that corrosion led to the rupture of a 36-year-old pipe and a subsequent fire at Chevron's refinery on Aug. 6, prompting renewed criticism from investigators about the company's failure to replace the worn piece of equipment.

The 109-page report, prepared by Anamet in Hayward, concludes that the 8-inch carbon steel pipe had low silicon content and was vulnerable to corrosion from crude oil heavy in sulfur.

"Based on the results of this evaluation," the report states, "sulfidation corrosion caused wall thinning that led to rupture."

** MANDATORY CREDIT ** The release of flammable vapor leads to a fire at the Chevron refinery in Richmond, Calif., on Monday, Aug. 6, 2012. (Fototaker.net
** MANDATORY CREDIT ** The release of flammable vapor leads to a fire at the Chevron refinery in Richmond, Calif., on Monday, Aug. 6, 2012. (Fototaker.net via Chemical Safety Board)

In a prepared statement, Ellen Widess, chief of the state Division of Occupational Safety and Health, also known as Cal/OSHA, said the latest 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."

Investigators also noted that Chevron workers responding to the leak may have exacerbated the problem by trying to fix it while the unit remained in operation. The corroded pipe may have been punctured when Chevron firefighters used sharp tools to strip away insulation in search of the leak, accelerating the release of gas oil.

The report comes as part of an ongoing investigation by the U.S. Chemical Safety Board, Cal/OSHA, the United Steelworkers union and Chevron.

Chemical Safety Board Chairman Rafael Moure-Eraso said in a statement Wednesday, "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."

In January, Cal/OSHA slapped the oil giant with $1 million in fines -- the biggest penalty in the agency's history -- for failing to replace the corroded pipe, not implementing its own emergency procedures and violations in leak-repair procedures.

Chevron spokesman Sean Comey on Wednesday said the report's findings are consistent with Chevron's internal probe.

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

But Chemical Safety Board officials have said the corroded pipe should have been replaced years earlier and that Chevron mismanaged the problem on Aug. 6. The smoky fire was sparked after the ruptured pipe leaked high-temperature gas oil and hydrocarbons, which soon ignited and resulted in six minor injuries on the site and sent more than 15,000 area residents to hospitals.

"Chevron should have shut down the crude unit as soon as a leak was observed and removed workers to a safe location," Moure-Eraso said. "Continuing to trouble-shoot the problem and having firefighters remove insulation searching for a leak -- while flammable hydrocarbons were flowing through the leaking piping -- was inconsistent with good safety practice."

The board's¿ investigation is ongoing, and a report detailing its findings is expected this year.

Assemblywoman Nancy Skinner, D-Berkeley, issued a statement Wednesday saying the report "demonstrates once again that Chevron has failed to properly monitor facilities and that the Richmond refinery fire could have been prevented."

Skinner didn't specify a particular course of action but wrote, "Monetary penalties alone may not suffice."

Chevron critics say the refinery was negligent and cut corners on maintenance.

"This latest report validates what we've all known, that sulfidation and poor monitoring played a key role in the fire," said Andres Soto of Communities for a Better Environment, a local watchdog group. "Not only did Chevron violate their own standards in not replacing a 40-year-old pipe, we are concerned that aging and vulnerable pipes are still in place throughout their system."

Chevron spokesman Comey said the refinery is committed to the highest safety standards.

"We want to be clear that our strong focus is on preventing a similar incident from happening in the future," Comey said. "We are implementing corrective actions that will strengthen management oversight, process safety, mechanical integrity and leak response."

Contact Robert Rogers at 510-262-2726 and follow him at Twitter.com/roberthrogers.