Pressure Hike; Gas Line Blows

Wednesday, October 26, 2011 @ 09:10 PM gHale

Just as Pacific Gas and Electric Co. (PG&E) was planning to boost gas levels on the pipeline to meet winter demand, a major gas transmission line serving the Bay Area ruptured during a pressure test Monday south of Bakersfield.

The 34-inch transmission line that runs from the Arizona border to Milpitas failed during a spike test at 9 a.m., blowing a crater in an alfalfa field near the town of Weedpatch, PG&E officials said.

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The line is one of two parallel transmission pipes that run to a major PG&E terminal in Milpitas and provide much of the Bay Area’s natural gas, officials said. A one-mile stretch was part of a test to ensure PG&E’s gas system is safe in the aftermath of last year’s deadly pipeline explosion in San Bruno.

Company officials said it was too early to tell whether gas supplies will suffer this winter as a result of the failure. They did not have a timetable for when they will be able to repair the pipeline and return it to service.

The pipe, known as Line 300B, failed because of a tear in a longitudinal seam — the same type of failure that caused the Sept. 9, 2010, explosion of a transmission pipeline in San Bruno that killed eight people, destroyed 38 homes and damaged 70 more.

Nick Stavropoulos, executive vice president of PG&E’s gas division, said the company did not yet know what caused Monday’s failure. The line ruptured at a double submerged arc weld, a type that Stavropoulos said is highly reliable if done correctly. The San Bruno line failed because of a seam weld that was only half as thick as the pipe itself.

At the time of the rupture, workers were trying to increase water pressure on the line to 1,040 pounds per square inch. When the pressure reached 998 pounds, a 4-foot-long portion of the longitudinal seam ruptured, creating an almond-shaped hole in the pipe and blowing a sizable crater in a farmer’s field, said PG&E spokesman David Eisenhauer.

The normal maximum pressure on the pipe was 757 pounds per square inch, but the California Public Utilities Commission ordered PG&E to cut that by 20 percent in February after an incident in which gas levels accidentally spiked at the pipeline’s compressor station near Needles.

The commission recently gave PG&E permission to restore full pressure on the line to meet winter demand after accepting water pressure tests at the compressor station as adequate, even though the testing was not at the level the company had agreed to with state regulators.

PG&E has been conducting pressure tests on portions of the line where it lacks records of previous strength tests.

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