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Politics & Government

Newly Released NTSB Records Confirm Piecemeal Pipe

The National Transportation Safety Board is exploring whether outside forces could have prompted the San Bruno pipe rupture.

The National Transportation Safety Board on Thursday released a 4,000-page cache of documents related to the rupture of a PG&E natural gas pipeline last year on Sept. 9.

The rupture and the fireball that ensued claimed eight lives and 38 homes, caused scores of debilitating injuries, and damaged 55 homes.

The documents include transcripts of conversations between gas line operators, interviews with former employees, sale receipts dating back to 1948, academic studies and reports detailing the size and composition of the pipeline materials.

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Perhaps most damning were pictures of pipes that had been crafted from short segments or "pups" and welded together.

After the explosion, PG&E officials claimed the pipeline was seamless.

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An early investigation revealed numerous longitudinal welds, and it emerged that no one at the utility company had inspected the pipes since .

Welds are not necessarily dangerous unless they are only inches apart, said Bob Bea, professor emeritus of engineering at UC Berkeley.

“In the case of the San Bruno pipeline, the pups were used to help make changes in the 'direction' or shape of the pipeline…the changes in direction introduce discontinuities that introduce higher than normal stresses.”

Documents in Thursday’s release also show the safety administration pursued PG&E's suggestion that an "external force"—specifically, a 2008 sewer replacement project using trenchless pipe—prompted the pipe to rupture.

Neither an analysis of ground movement nor comparative pressure readings indicate impact from an unrelated event likely proved to be "the triggering incident."

The city last week by independent investigators that accepted the theory without question, calling it "pseudo-science."

“The analytical work I have done does not indicate that the sewer installation stresses were significant in developing the final failure, (but) other modes of failure,” namely “fatigue induced crack growth that was caused by the very poorly welded and fabricated pup joint sections,” Bea said Friday.

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