Major PG&E gas line ruptures during hydro test
by Jaxon Van Derbeken, San Francisco Chronicle
A major Pacific Gas and Electric Co. gas transmission line serving the Bay Area ruptured during a pressure test Monday south of Bakersfield, just as the company was planning to boost gas levels on the pipeline to meet winter demand.
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 (Kern County), PG&E officials said.
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 say. A one-mile stretch was being tested as part of PG&E’s effort to ensure that its 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 repairs would be made and the pipe returned to service.
Similar to San Bruno
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.
"Our plan would be to cut out the section, get it replaced and get the (pressure) tests back going," Stavropoulos said. "It’s typically not an extensive process. Here, access should not be an issue, so it shouldn’t take very long."
A PG&E crew had shut down the gas flow to the 1950-vintage pipe and was testing its strength using high-pressure water. The test is a common one for determining whether welds that hold longitudinal seams together are strong, but it is one PG&E seldom used before the San Bruno disaster.
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.
Pressure had been cut
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 (San Bernardino County).
The commission had recently given 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 they had not been done to 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.
To the consternation of regulators, PG&E had conducted a string of non-spike tests on portions of Line 300B in recent weeks, saying conventional spike tests could endanger the pipeline. The company said last month that it had done at least seven tests to below spike levels on the pipeline and the parallel Line 300A and announced plans to do more such tests on the lines.
The stretch of line that failed Monday, however, ruptured during a full spike test, Eisenhauer said.
First test failure
PG&E has said it intends to run pressure tests on 152 miles of transmission gas lines by the end of December and on hundreds of additional miles over the next few years. Stavropoulos said Monday’s failure was the only one so far among 6o pressure tests performed on 120 miles of line since the San Bruno explosion.
"This is the first one – but that’s what these tests are intended to do, identify areas of weakness," Stavropoulos said. "The message I read into this is that the hydro tests are serving a purpose: to validate that a line is fit for service with a significant margin for safety."
The area where the rupture occurred Monday is about 20 miles north of where PG&E experienced five unexplained leaks on the line in the 1950s, company documents show. It was not immediately clear whether the tests that PG&E has been conducting recently on the line established that stretch of pipe as safe.
The failure occurred as PG&E officials were reviewing more than 80 pages of documents that California regulators recently identified as suggesting that the company used salvaged or "junked" pipe in its system in the 1940s and 1950s.
Regulators provided the documents Saturday after PG&E said it was not aware of any instances in which scrapped, substandard pipe had been put in the ground.