A crack stemming from an overstressed weld on the seam of the Pacific Gas and Electric (PGE) pipeline may have played a part in the deadly explosion last September in San Bruno, CA, according to a report issued by the National Transportation Safety Board.

“The crack initiated in a manner consistent with ductile overstress from the root of the weld,” said the NTSB, which is investigating the Sept. 9 explosion that killed killed eight people, injured 52 people and destroyed 37 homes (see Daily GPI, Sept. 13, 2010).

The “Metallurgical Group Chairman Factual Report” is the first in a series of factual reports that the board will release on the rupture and explosion. It merely states the facts and draws no conclusions.

Additional reports on operations, human performance, survival factors, fire scene and meteorology will be released on the first day of a three-day fact-finding hearing that NTSB will hold March 1-3 in Washington, DC.

“Additional work still lies ahead before the NTSB will reach a final conclusion, and it’s premature for PG&E or anyone to speculate on what caused this accident. Nonetheless, today’s report is an important step in the effort to answer that crucial question,” said PG&E President Chris Johns. He noted that the utility is continuing to work closely with NTSB.

“We want to remind our customers and the communities…we serve that all pipelines in PG&E’s system that are of a similar size and vintage to the line in San Bruno and have not been pressure tested, are continuing to operate at pressures that have been reduced by 20%. This measure builds a significant additional margin of safety into our current operating conditions,” Johns said.

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