Pacific Gas & Electric ends intentional gas-line pressure spikes

SAN FRANCISCO, Calif. - Pacific Gas and Electric Co. said on Jan. 10 that it has suspended the practice of boosting pressure on its natural-gas transmission lines to the legal limit, an announcement it made one day after The Chronicle reported that such a spike may have weakened the San Bruno pipeline before it ruptured.

The Chronicle reported on Jan. 9 that on Dec. 9, 2008, PG&E intentionally boosted gas pressure on the San Bruno line for two hours to the maximum legal limit of 400 pounds per square inch. That was more pressure than PG&E has ever acknowledged using on the line, which it normally ran at 375 pounds per square inch.

The utility said the spike was "part of our operating practice," and that it runs its lines at their maximum once every five years. It did not elaborate on its reasons for doing so.
Experts interviewed by The Chronicle said the 2008 surge could have exacerbated any existing weaknesses on the San Bruno line, making it more vulnerable to failure in a subsequent pressure spike.

The next spike happened on Sept. 9, when a malfunction caused a surge to 386 pounds on the pipeline running from Milpitas to San Francisco.

The spike coincided with the rupture of the San Bruno section of the pipe and an explosion and fireball that killed eight people and destroyed 38 homes.

"We have suspended the practice of increasing pressure on a transmission line to ensure (its) operational flexibility, pending the outcome" of the National Transportation Safety Board's investigation into the explosion, PG&E spokesman Brian Swanson said on Jan. 10.