Just 719 feet south of the spot where a poorly welded section of gas transmission pipeline No. 132 blew up last year in San Bruno, killing eight and razing dozens of homes, lay another segment of the pipe that had a similar — and similarly unknown — defect.
Federal inspectors with the National Transportation Safety Board, the agency tasked with uncovering the cause of the blast, reported the discovery of the poor weld — within about a block of the blast site — as part of 4,000 pages of documents made public Tuesday.
The inspectors’ report stated that after the blast, a camera had been run through PG&E’s pipeline 132 to look for other potential flaws. Inspectors observed that “no identifiable internal seam could be visually detected” for the nearby 10-inch section of pipe.
That section, along with 3-foot lengths of pipe on either side, was removed from the ground and flown to their laboratory in Virginia, where it was inspected in April.
The girth welds that connected the 10-inch segment to the sections on either side of it appeared to only have been welded on the outside, rather than from both the outside and the inside, as is standard. Similarly, a longitudinal seam at the blast site was found to have only been welded on the outside, not the inside, NTSB has stated.
The report concludes that the flaws weakened the pipe below required standards. PG&E has conceded that an unrelated problem upstream of the blast spiked the pressure running through the pipe just before it ruptured, though it’s still unclear by how much.
Weld problems were also found when the same pipe leaked in 1988, and were discovered more recently during an inspection PG&E did on its pipeline in South San Francisco. Documents the company turned over to the California Public Utilities Commission last month revealed still more weld problems on the pipe.
PG&E spokesman David Eisenhower said the utility is “taking a look at our whole system,” and has taken many steps to improve the safety of its pipelines since the fatal blast. Among those steps is to lower the pressure through several of its lines in the Bay Area.
Richard Steffen, district director for Congresswoman Jackie Speier, said it’s hard to interpret exactly how serious the welding problem may be because NTSB did not add any analysis to their findings. But it also raises the question of exactly how widespread weaknesses in PG&E’s pipes may be, he said.
“Welds were bad in [this section] of pipeline — my guess is it’s bad in similar sections nearby,” he said.