Pacific Gas & Electric (PG&E) successfully repaired a gas pipeline leak, which had been discovered in Palo Alto earlier this month. The leak, which was 1 to 2 mm in diameter, was the result of water corrosion and was discovered during a routine pressure test.
The faulty pipeline segment was part of the same line–line 132, which caused a September 2010 explosion in San Bruno and killed eight people. That incident resulted from an incomplete weld on a pipeline seam, which ruptured in response to an electronic glitch elevating the gas pressure in the pipeline.
The pipeline is one of two PG&E lines that run along Stanford campus. The pipelines run on either side of Junipero Serra Boulevard from Page Mill Road to Sand Hill Road, through an area that hosts faculty residences.
Both pipelines were listed by PG&E on a list of 100 top sections for maintenance compiled after the San Bruno explosion. PG&E plans to replace line 109 and line 132, which date from 1936 and 1947 respectively, by 2013 and 2014. PG&E also plans to upgrade line 109 to allow internal inspection of the pipe’s structural integrity.
The leak in the pipeline, which occurred under Page Mill Road in Palo Alto, was discovered on Nov. 3 when a routine test using elevated water pressure revealed gradually falling pressure levels through the pipe segment. The leak’s precise location was determined on Nov. 8, by pumping a helium-air mixture through the pipeline and testing at ground level for traces of the mixture.
The line was retested, without any further faults discovered, on Nov. 10. No gas leak resulted from the pipe, which had been drained before the test commenced.
“They welded a sleeve around it [the leak],” said PG&E spokesperson Brittany Chord. “The line was able to resume service shortly. The repair process was only a matter of a couple of days.”
Chord described the fault as relatively minor, with the size of the leak likely being exacerbated by exposure to above-normal pressure during the testing process. The pipeline had been tested earlier in the year without issue. However, PG&E officials informed Stanford earlier in the year that they had been unable to find testing records for most of the lines along Junipero Serra.
In response to the San Bruno explosion, California state regulators ordered that hydrostatic testing, which pumps water at 50 percent higher pressure through the line for eight hours, be performed on all pipeline segments without documented test results. The method, which costs between $600,000 and $1 million per mile of pipes tested, offers greater accuracy than comparable methods and will gradually be applied to PG&E’s entire network in order to determine where pipe upgrades or replacement may be most needed, according to Chord.
Larry Gibbs, associate vice provost for Environmental Health and Safety, noted that both lines crossing Stanford property were operating at reduced pressure following an order from the state government, but that the University considered the leak to have been effectively addressed.
“We’re all very confident in [on-campus] pipeline safety,” Gibbs said. “The [new] testing process is certainly something that we’ve pushed PG&E for.”
Gibbs noted that there had been previous incidents with pipeline leaks on campus. Fence construction near Casa Italiana and the installation of fiber optic cables by Residential Housing both resulted in minor pipeline breaches, which Gibbs said were resolved within a couple of hours by PG&E repair teams.
“We’ve been working with PG&E for over a year,” Gibbs said. The dialogue, which was established after the San Bruno explosion, has involved regular meetings with a PG&E representative. Stanford has sought to coordinate with PG&E with regards to on-campus construction and pipeline repair in order to preclude further incidents.