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NTSB Reports Lack of Coatings, Bad Welds in CA Pipeline Blast

Monday, January 24, 2011

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The National Transportation Safety Board has found faulty welds, sagging coatings, and large uncoated areas on Pacific Gas & Electric natural-gas pipelines that exploded in September.

PG&E records had described the underground pipe as seamless, and the NTSB is now combing those records.

The explosion in San Bruno, CA, killed eight people and leveled 38 homes on Sept. 9.

The NTSB has issued no cause for the blast, but attention has been focusing on the pipe’s condition.

In a 77-page Metallurgical Group Chairman Factual Report issued Friday (Jan. 21), NTSB described in detail the condition and quality of welds and coatings along three ruptured sections of 30-inch diameter pipe excavated from the blast area. The sections are 12’4”, 27’8” and 15’9” long.

The report did not analyze the results or offer conclusions.

Pipe Coating

Large areas of pipe were missing coating altogether—one uncoated area started 3’4” from the cut end and continued to the fractured end, the board said. Another section was missing coating “on much of the sides and bottom.”

Coating on the top half of the pipe close to the fracture “exhibited features consistent with drips, sags and charring…. The coating flow patterns were complex with longitudinal and circumferential flow occurring in different regions.”

In one area, a 32-inch piece of coating was detaching from the pipe; another area had an 18-inch-wide strip of coating peeling off less than six feet from one of the fractured areas. “There were also regions on the underside where no coating was observed and the pipe surface was visible,” NTSB reported


It added: “No coating was observed over a cluster of small patches each approximately 2 inches in diameter. …  Similar areas of no coating were observed on the undersides of pups 1, 2, and 3.”

Where coating was used, the appearance “was consistent with hot applied asphalt, parts of which had been exposed to elevated temperatures,” NTSB said.

Numerous Defects

Although the utility company records said the pipe was seamless, NTSB found evidence of numerous girth and seam weld defects, including lack of penetration, incomplete fusion, burn through, slag inclusion,  crack, porosity, undercutting, and excess reinforcement.


“All girth welds exhibited incomplete fusion, slag inclusion, and porosity defects on at least one radiograph,” the report said. Lack-of-penetration defects and undercutting defects were exhibited on all but two intact girth welds, the board reported.

For the first time, the report also identified a seam weld as the site of the rupture and said the weld was half as thick as it should have been. The weld would have been considered inferior even by the standards of 1956, when the pipe was installed, the San Francisco Chronicle reported.

Pipes of ‘Unknown Origin’

“PG&E's records—shown by investigators to be in error—indicated that the line was seamless, when in fact the San Bruno site was part of a cobbled assortment of potentially inferior 4-foot-long seamed pipes of apparently unknown origin,” the Chronicle said.

“Records for hundreds of miles of pipelines elsewhere in PG&E's system are now under scrutiny, and regulators might compel the use of high-pressure-water testing to seek out similar weld flaws.”

UC Berkeley engineering Professor Robert Bea told the newspaper that “the seam weld was so weak on the 3/8-inch-thick pipe that a disaster could have occurred at any time.”

‘Horrible Welding’

"It's not bad welding; it's horrible welding," said Bea, a trained welder. Based on what Bea knew of the welds from reading the report, the newspaper said, the legal maximum pressure on the line should have been "zero."

PG&E President Chris Johns said Friday that it was “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.”

Johns noted that all of the pipelines in PG&E’s system “are of a similar size and vintage to the line in San Bruno and have not been pressure tested” but are operating “at pressures that have been reduced by 20%,” which “builds a significant additional margin of safety into our current operating conditions.”


Tagged categories: Explosions; Health and safety; Paint application; Pipeline; Pipelines; Quality control

Comment from Mark Baum, (1/25/2011, 9:48 AM)

Is this what the great USA is coming to?? People not caring about quality, just the price and if it is done on time. Our youth is being trained to do jobs and one important thing is being left out: PRIDE IN THEIR WORK and RESPECT FOR HUMAN LIFE! Would an oldtimer weld a pipe and not care if it is a quality job, if it will last a lifetime or kill someone? I think not. The work force here is slowly going downhill like our youth, they are not caring what happens tomorrow, just what they can get out of today. This is not all their fault, because someone tried to teach them and the system failed. If we as Americans do not wake up and see what is happening and try to change it, then we deserve what we get.

Comment from Gavin Hepp, (1/25/2011, 10:47 AM)

It looks like the coating was applied with a butter knife. The installing party of this pipe needs to be identified.

Comment from Patty Killpack, (1/25/2011, 10:57 AM)

To Mark Baum: This was done in 1956; they are old guys.

Comment from Car F., (1/25/2011, 10:59 AM)

I always tell my crew to do a good and thorough job, because if something goes wrong, no one will remember how quickly or under the budget was the job completed. Everyone will say "who was the idiot that did this?" Sadly, budget constraints and avaricious expectations result in poor quality work and unprofessional [or lethal] results.

Comment from David Johnson, (1/26/2011, 10:31 AM)

The welding was lousy. The inspection was lousy. I want to know why 7 "pup" rings were welded together. This was an accident waiting to happen. Regarding the coatings, remember, this pipe exploded and was exposed to a lot of heat over an extended period of time. I would expect the coating to destroyed. David Johnson Chief Metallurgist

Comment from Tom Schwerdt, (2/2/2011, 10:04 AM)

David, The coating really doesn't look like it was burned away; I would expect significantly different patterns of remaining coating if this was burn loss. This just looks like a sloppy, slap-it-on-sort-of job.

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