Get SF Weekly Newsletters

Tuesday, December 14, 2010

San Bruno Fire: NTSB Issues Second Accident Report

Posted By on Tue, Dec 14, 2010 at 10:15 AM

No, the investigator hasn't rested his water bottle on the pipeline. He's 'cleaning a fracture surface.' - NTSB
  • NTSB
  • No, the investigator hasn't rested his water bottle on the pipeline. He's 'cleaning a fracture surface.'

The National Transportation Safety Board moments ago released an update on "Accident No. DCA10MP008"-- the Sept. 9 San Bruno PG&E pipeline explosion and fire.

Those hoping for a clear explanation of why an entire neighborhood was transformed into a hellish inferno will have to keep waiting. This report mainly concerns itself with highly technical explanations of how various expert bodies inspect welds and seams on incinerated pipes.

Speaking of welds, it seems PG&E wasn't aware that the pipes in question had them. "PG&E survey sheets and charts for the rupture location indicate that

the pipeline was constructed of 30-inch-diameter seamless steel pipe

(API5L Grade X42) with a 0.375-inch thick wall," reads the NTSB report. "Evidence obtained so

far, however, indicates the pipeline in the area of the rupture was

constructed, at least in part, with seam-welded pipe."

The ramifications of that revelation are unclear. What's more obvious is that assigning blame for the explosion will be a drawn-out and meticulous affair. Per the report:

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 in the ruptured pipe pieces.


So much for those apocryphal tales of gas odors pervading the neighborhood prior to the blast.

Investigators also used a variety of methods to inspect the welds and seams on the ruptured pipeline. "Metallurgists are currently in the process of using this information to determine the direction of crack propagation and the fracture origin and failure mechanisms." In other words, they're working on that.

Finally, "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." This may not be unusual, however. The NTSB is currently researching whether this was just how they did things back in 1956, when the pipe in question was installed. 

click to enlarge The 28-foot-long ruptured section of pipeline at the NTSB Training Center in Ashburn, Va. - NTSB
  • NTSB
  • The 28-foot-long ruptured section of pipeline at the NTSB Training Center in Ashburn, Va.
An October 13 preliminary report on the conflagration noted an electrical disruption cut power to the regulating valve for the ill-fated Line 132 -- but the pressure in the pipeline never exceeded the red level of 400 pounds per square inch. Overall, that report did not come up with any, smoking guns, if you can pardon the expression. And neither has this one.

Still under investigation:

  • Chemical compositional analysis and mechanical property testing of samples taken from the ruptured pipe pieces.
  • Evaluation of environmental factors at the accident site.

Per the NTSB: "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."

So it would seem.

Follow us on Twitter at @TheSnitchSF and @SFWeekly





  • Pin It

Tags: , , ,

About The Author

Joe Eskenazi

Joe Eskenazi

Bio:
Joe Eskenazi was born in San Francisco, raised in the Bay Area, and attended U.C. Berkeley. He never left. "Your humble narrator" was a staff writer and columnist for SF Weekly from 2007 to 2015. He resides in the Excelsior with his wife, 4.3 miles from his birthplace and 5,474 from hers.

Comments

Subscribe to this thread:

Add a comment

Popular Stories

  1. Most Popular Stories
  2. Stories You Missed

Like us on Facebook

Slideshows

  • clipping at Brava Theater Sept. 11
    Sub Pop recording artists 'clipping.' brought their brand of noise-driven experimental hip hop to the closing night of 2016's San Francisco Electronic Music Fest this past Sunday. The packed Brava Theater hosted an initially seated crowd that ended the night jumping and dancing against the front of the stage. The trio performed a set focused on their recently released Sci-Fi Horror concept album, 'Splendor & Misery', then delved into their dancier and more aggressive back catalogue, and recent single 'Wriggle'. Opening performances included local experimental electronic duo 'Tujurikkuja' and computer music artist 'Madalyn Merkey.'"