The group headed by the National Transportation Safety Board investigating the Sept. 9 natural gas pipeline rupture and explosion that killed eight people in San Bruno released an interim report that ruled out outside corrosion and damage caused by a third party as the cause for the blast, but found that part of the pipe near the rupture was constructed with seam-welded pipe, which owner Pacific Gas & Electric reported as seamless.
The group, chaired by the NTSB, includes technical experts from the Pipeline and Hazardous Materials Safety Administration (PHMSA), the California Public Utilities Commission (CPUC), and PG&E. PG&E survey sheets and charts for the rupture location indicate that the pipeline was constructed of 30-in.-diameter seamless steel pipe (API5L Grade X42) with a 0.375-in. thick wall. Evidence obtained so far, however, indicates the pipeline in the area of the rupture was constructed, at least in part, with seam-welded pipe, says the NTSB.