Regulators have ordered Plains All American Pipeline to empty corrosive crude oil that’s been sitting in Line 903 since it was partially shut down in late May.

The U.S. Department of Transportation’s Pipeline and Hazardous Materials and Safety Administration issued on Nov. 13 an amendment to the original corrective action order requiring that Plains purges its 130-mile pipeline that runs from Gaviota to Kern County.

The rust inhibitor in the crude oil started wearing down in November, the order says. PHMSA did not specify why the line was not cleaned out earlier.

“This unprocessed crude may contain water, natural gas and other impurities that contribute to internal corrosion,” the order reads. “According to Freeport (McMoRan), the biocide and rust inhibitor in this crude oil will begin to lose effectiveness around November 2015, adding to the risk of accelerated internal corrosion on Line 903.”

Extensive corrosion is what may have caused Line 901’s rupture on May 19, according to PHMSA. Line 901 connects to Line 903, which has also shown signs of deterioration during three internal inspections in 2013 and 2014, regulators say.

“A PHMSA independent review of Plains Pipeline’s in-line inspection surveys discovered instances where the tool miscalculated the degree of corrosion occurring in specific portions of Lines 901 and 903,” the order reads. It continues to say that the tool underestimated the corrosion.

It’s common practice to share data from the inspection tool with its vendor to validate the results, according to PHMSA, but Plains withheld the information so “it could enhance its interpretation of the data,” the order reads.

Line 903 ceased operation on May 28, except for a 15-mile section from Pentland to Emidio that is operating intermittently at a reduced pressure. The pipeline will remain shut down after it is cleaned out, tested and filled with inert gas that aims to prevent further degradation, according to the order.

If Plains does not contest the order, it has 15 days to submit a purge plan. An independent certified contractor must check the pipeline’s corrosion levels.

“It does not appear that Plains has an effective corrosion control program,” the order reads.

PHMSA’s investigation is ongoing. Pipeline investigations take an average of 20 months, the administration said.

• Contact Alex Kacik at akacik@pacbiztimes.com.