SAN JOSE, Calif. -- California regulators issued an order Thursday forcing PG&E to reduce pressure in two natural gas transmission lines in the San Francisco Bay Area by 20 percent, just days after the release of a report raising safety questions about a similarly constructed pipeline that exploded in San Bruno on Sept. 9, killing eight.
PG&E said it will take steps immediately to comply.
The order from the California Public Utilities Commission comes as a cold snap descends on the Bay Area, which will likely increase demand for natural gas just as the cuts take effect. "We can comply with the CPUC directive and continue to reliably serve our customers," said PG&E spokesman Denny Boyles, though he acknowledged that reducing service to some nonresidential customers could not be ruled out.
"If there was an unexpected weather event we would have to look at that," he said. PG&E has already reduced pressure in its transmission lines in the area in response to concerns that a pressure surge may have played a role in the deadly blast.
Boyles said a pipeline that runs from Oakland to Fremont, known as Line 153, and a line from Fremont to Milpitas, called 131, are the only ones subject to the pressure reduction, which applies to pipelines with characteristics similar to the one in San Bruno that have not already had their pressure cut.
In a report Tuesday, the National Transportation Safety Board raised safety concerns about the types of welds used in the San Bruno pipeline.
The board's investigators discovered that PG&E's records incorrectly described the San Bruno section of pipeline that ruptured as seamless, when at least portions of it were seam-welded. Seam-welded pipes can have more problems than seamless pipes, according to experts.
The inspectors also said that some of the damaged San Bruno pipe segments were welded only on one side, and some on both. One expert said this week that he was surprised by this, since double-sided welding is more effective.
Before pressure can be restored, the lines must be either pressure tested, X-rayed, examined with cameras, or inspected using a robot "smart pig" or other technology that can assess seam integrity. The PUC is calling for extensive testing that could take months.
Experts said the directive was confusing and that some of the methods specified won't detect all potential flaws in the pipelines.
Theo Theofanous, a chemical and mechanical engineering professor at the University of California, Santa Barbara, who served on a federal panel assessing pipeline risks, criticized the PUC for asking PG&E to select the pipelines to be inspected. "Why would anybody believe they know what they're doing?" he asked.
An internal camera "would tell you if you have a weld or not -- it doesn't tell you if it's good or not," said Richard Kuprewicz, a Washington state pipeline safety expert. Another expert, Oliver Moghissi, president-elect of the National Association of Corrosion Engineers, said single-sided seam welds on older pipelines "doesn't mean that a mistake was made." That type of welding was common at one time, he said, although double-sided welding is the most common type.
Rep. Jackie Speier, D-Calif., whose district includes San Bruno, called the order "a welcome step for safety, although much delayed." Speier noted that the PUC is ordering PG&E to use methods other than the "direct assessment" it has defended. Direct assessment involves checks for corrosion protection by inspectors walking above buried pipelines.
That technique does not detect defective welds and is dependent on accurate knowledge of the pipe underneath. "There is still concern over the accuracy of PG&E records that identify what type of pipes are underground," Speier said.
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