The segment of pipe that failed during a pressurized water test Sunday was apparently damaged by a backhoe sometime in the past 60 years, according to PG&E officials, but when exactly is unknown.
No one was injured when a segment of Line 132 exploded at 3:20 p.m. off Interstate 280 near Woodside, but it created a mudslide that closed northbound lanes for hours. It also left a 5-by-5-foot crater roughly 100 yards from homes.
The segment is some 20 miles south of the site where another part of Line 132 exploded in San Bruno in September 2010, killing eight people and destroying a neighborhood.
Sunday’s incident is the third failure to be found in PG&E pipes since the utility started hydrostatic pressure tests last month. On Oct. 24, a similar rupture occurred in an alfalfa field near Bakersfield on Line 300B. Then on Friday, a pinhole was found in a four-mile stretch of Line 132 between Menlo Park and Palo Alto.
PG&E spokesman Brian Swanson said that hole and the rupture Sunday are from two different segments, and crews are still working to find and fix the pinhole.
After the San Bruno incident, the federal government criticized PG&E for its “litany of failures” in testing and record-keeping — the San Bruno pipe was originally thought to be seamless, but later found to have a longitudinal seam. The utility was ordered to test Line 132 and pipes that did not have records but had similar characteristics.
Swanson said Sunday’s ruptured pipe had a dent that was likely caused by a third-party contractor using a backhoe sometime after the seamless pipe was installed in 1947.
But regardless of the recent failures, Swanson called the testing a success. “This is why we do this kind of testing,” he said, “to know we have a significant margin of safety under normal operating pressure and to find flaws.”
The segment failed at a pressure of 550 pounds per square inch, according to Swanson. Before the test, it was operating at 300 psi. The test would have put the pressure at 700 psi for eight hours. The segment in San Bruno blew up at 375 psi.
Pressure tests gauge gas pipeline safety at a “level far in excess of … normal operating pressure,” according to spokeswoman Terrie Prosper of the California Public Utilities Commission, which regulates PG&E.
Pipeline safety expert Richard Kuprewicz said it’s not uncommon to find such a flaw that caused Sunday’s rupture 60 years after installation.
“No pipeline is free of imperfections,” Kuprewicz said.