PG&E gas line ruptures during pressure test
October 26, 2011
A major PG&E gas transmission line ruptured during a pressure test Monday south of Bakersfield as the utility was planning to boost gas levels on the pipeline to meet winter demand. [SF Chronicle]
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 Kern County town of Weedpatch, PG&E officials said.
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 what is known as 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.
Monday’s failure was the only one so far among 6o pressure tests performed on 120 miles of line since the San Bruno explosion.