Santa Barbara spill caused by external corrosion of oil pipe

External corrosion on an oil pipeline was the root cause of a leak that spilled more than 140,000 gallons of crude on the Santa Barbara coast in May, federal regulators reported Wednesday.

The spill occurred after pumps on the Plains All American Pipeline — a company with a history of violations — were shut down and restarted, sending a larger volume of oil surging through the 2-foot-wide pipe at higher pressure, the Pipeline and Hazardous Materials Safety Administration said in preliminary findings. After the leak occurred, however, and plunging pressure in the pipeline triggered an alarm, it wasn't shut down for more than 30 minutes.

Plains wouldn't comment on the report because of ongoing investigations of the spill, a spokeswoman said. Local, state and federal prosecutors are probing the spill and regulators could issue fines against the Texas-based company.

The Santa Barbara coastline was the scene of a much larger spill in 1969 — the largest in U.S. waters at the time — that is credited with galvanizing the American environmental movement.

Reports of corrosion of the underground pipe and pump problems were previously disclosed, but regulators hadn't labeled corrosion as the root cause of the leak, pinpointed the precise moment the pipe failed or provided a timeline of how long it took to shut down the pipe.

The spill two weeks before the popular Memorial Day weekend forced the state to close popular beaches as the oil fouled a pristine stretch of coastline and an oil sheen spread over miles of the Pacific Ocean. More than 300 dead animals, including pelicans and sea lions, were recovered after the spill that sent tar balls drifting more than 100 miles away to Los Angeles beaches.

A pipeline leak monitoring system had been turned off at the control center, the report said, though it noted that was still under investigation.

Richard Kuprewicz, a pipeline safety expert, said there could be a good reason for it being off, but it's potentially significant.

"'Turned off' is the magic word," Kuprewicz said. "Why this was turned off would be a valid question."

The agency said it would provide more details when it issues a final report this spring.

Kuprewicz said it struck him that the pipe failed when it was only pumping at about 50 percent of its maximum operating pressure. That indicated to him that there were problems on the pipeline.

A chart in the report showed corrosion anomalies grew and intensified between surveys in 2007, 2012 and the last tests just weeks before the leak.

Robert Bea, an engineering professor at University of California, Berkeley, questioned how Plains could operate in a sensitive environmental area — through scenic hills and near the beautiful coast — with "severely corroded" pipeline.

Gov. Jerry Brown declared a state of emergency in Santa Barbara County due to the effects of the spill which occurred during marine mammals’ migratory season, when humpback whales, sea lions and porpoises typically swim through the affected area. Clean-up efforts proved difficult.

"I think the answer to this question will show that the root causes of this accident are firmly rooted in organizational malfunctions that resulted in underestimates of the likelihoods and consequences of a breach in Line 901," Bea wrote in an email.

The report also noted that the spill, originally estimated at up to 100,000 gallons, had dumped 142,800 gallons.

Al Jazeera with The Associated Press