Pacific Gas & Electric is blaming “isolated” corrosion for a new leak in one part of the infamous San Bruno, CA, transmission pipeline, while working to repair and recoat two other segments that ruptured recently.
The leak area, described as a 1-2 mm hole surrounded by a three-quarter-inch pocket of corrosion, was discovered in a four-mile segment of pipe near Palo Alto during a recent series of hydrostatic tests.
|Hydrostatic testing has caused two ruptures and uncovered one leak in recent weeks along the same transmission line that exploded last year in San Bruno, CA.|
PG&E has been performing pressure tests since April on 150 miles of its Line 132, which ruptured catastrophically in September 2010, killing eight people and flattening dozens of homes.
Experts say PG&E could have prevented the disaster by conducting pressure testing on the line, which had sprung dozens of leaks over several decades.
Instead, prior to the explosion, PG&E had been using cheaper, simpler corrosion inspections on the line.
PG&E declined to comment on whether the corroded area had been coated and, if so, when. Although a faulty longitudinal weld was considered the primary cause of the San Bruno explosion, the National Transportation Safety Board investigation also turned up coating flaws in the line.
Kirk Johnson, vice president of gas transmission maintenance at PG&E, dismissed the leak in the 24-inch segment as “isolated external corrosion,” probably caused by water penetrating the pipe’s asphalt wrapping.
|Federal investigators found segments of Line 132 uncoated and poorly coated.|
"Our preliminary investigation tells us we had a small leak in the wrap and a very small amount of water got in," causing "some pretty serious" loss of wall thickness, Johnson said.
"The rest of the pipe, some of it looked brand new," he told the San Jose Mercury News.
The pipe has been repaired, and pressure testing has resumed, PG&E spokesman Brian Swanson said.
"We welded a steel band around the pipe and over the pinhole," Swanson said. "The steel band acts as a protective barrier."
The company is also working to repair a segment from the same line that ruptured within days of the discovery of the Palo Alto leak.
That line blew during pressure testing Nov. 6 along I-280 in Woodside, raining mud, rocks and debris on the highway and shutting it down.
Crews spent most of last week cutting out the damaged section of pipe and replacing it, said Swanson. After the utility tests the segment again, workers will spend several days putting a protective coating on the pipe and filling in the seven-by-seven-foot hole it created.
PG&E has tentatively blamed that rupture on an unknown third party working with a backhoe.
"We'll do a full investigation, but clearly the line had been hit with something mechanical," causing a tear in the protective asphalt wrapping, Johnson said.
Meanwhile, PG&E is still fielding questions about yet another rupture along a longitudinal seam in a 61-year-old segment of pipe Oct. 24 in Bakersfield.
PG&E waited more than eight hours before notifying the public of that rupture, which occurred along a double submerged arc welded seam well before the utility reached maximum pressure in the testing. A spokesman said the utility released the information as soon as it could.
That segment, too, is in the process of being repaired and retested.
However, Swanson said the utility will conduct spike testing—in which a burst of extreme water pressure is followed by sustained above-average pressure— only if PG&E determines that testing will not damage the segment.
Critics remained concerned and urged the California Public Utility Commission to hold the utility accountable. Among them was Mindy Spatt, spokeswoman for the Utility Reform Network, or TURN, a frequent critic of PG&E.
Said Spatt: "If there was a bad weld in San Bruno and there was a bad weld in Bakersfield, where else is there a bad weld?"