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NTSB Investigation Update on San Bruno Explosion

| December 14, 2010
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Section of ruptured pipeline at NTSB lab

UPDATE 12:00 P.M. The Chronicle has gleaned some new info from the NTSB update on its investigation into the San Bruno pipeline explosion and subsequent fire.

…The report does…express concern about the “seam weld” in the ruptured section of pipe, which was installed in 1956.

The pipeline that ruptured was constructed – as all pipes were at the time – by fabricators who curled a flat piece of metal around a cylinder and joined the sides together.

A 28-foot length of the line that blew out of the ground had five individual pipes – one bigger section and four smaller pieces, known as pups – welded together to allow the line to change direction with the hilly terrain.

“Investigators found that while the longitudinal seams on some of the pipe segments were fusion-welded from both inside and outside the pipe, some were fusion-welded only from the outside of the pipe,” the report says.

It continues: “In order to understand this variance, investigators are in the process of researching pipe welding standards and practices in effect at the time the pipeline was installed in 1956.”

and…

…the report may put to rest complaints by some residents of the Crestmoor neighborhood of San Bruno that they had heard reports that natural gas was leaking in the days before the explosion. The federal investigators say that “no physical evidence suggests that a pre-existing leak occurred in the ruptured pipe pieces.”

The Wall Street Journal puts it this way:

Pieces of a pipeline involved in a September explosion near San Francisco show unusual variations in the welds, the National Transportation Safety Board said Tuesday.

The board also noted discrepancies between utility records concerning the kind of pipe used and what investigators pulled from the ground after the accident.

Earlier post:

The NTSB has released an update of its initial investigation into the San Bruno gas pipeline explosion that killed eight people and destroyed dozens of homes in a subsequent fire.


The information provided is rather technical and not necessarily easy to follow, but one thing is clear: Not only does the agency not yet know what caused the fatal event, it may not come to a final conclusion for some time.

The investigation is still in an early phase and there is much factual information to be developed before the Safety Board is positioned to determine the probable cause of the accident.

Today’s release focuses on the examination of ruptured pipe pieces. Here is the crux of the findings:

Investigators found that while the longitudinal seams on some of the pipe segments were fusion-welded from both inside and outside the pipe, some were fusion-welded only from the outside of the pipe. In order to understand this variance, investigators are in the process of researching pipe welding standards and practices in effect at the time the pipeline was installed in 1956.

The outer surfaces of the ruptured pipe pieces revealed no evidence of external corrosion. No dents, gouges, or other physical indications consistent with excavation damage were observed. Additionally, no physical evidence suggests that a pre-existing leak occurred in the ruptured pipe pieces.

Sounds like a lot of negative findings. The NTSB is also investigating as possible causes: “pipeline control and operations, regulation and oversight, human performance, survival factors, and pipeline maintenance and records.”

UPDATE 11:21 PM: AP says Jackie Speier is holding a press conference on the findings today.

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Category: Environment, News

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