The gas pipeline blast that left eight dead and destroyed 38 homes in San Bruno, CA, would have happened even if Pacific Gas and Electric Co. (PG&E) had kept accurate records of the line, company officials testified Monday.
The rupture on the 30-inch transmission line that caused the Sept. 9 explosion took place at an incomplete weld on a pipe seam, metallurgists with the National Transportation Safety Board (NTSB) found. PG&E’s records showed the pipe had no seams, and it never conducted inspections that might have detected a flawed seam weld.
Even though the utility didn’t have a record of the weld on the pipe, this type of weld does not have a record of failing, PG&E told the state Public Utilities Commission. As a result, it said, the company still would have picked an inspection technique best suited for finding the problem that PG&E considered the greatest threat to the line — corrosion — and not flawed welds.
“The question becomes whether the correct seam type information … would have changed PG&E’s assessment methodology” and “potentially prevented the Sept. 9, 2010, San Bruno pipeline rupture,” the company said. “The short answer to that question is ‘no.’ ”
The utility is in the midst of checking for records on its pipelines in and around urban areas. PG&E failed to meet a March 15 state deadline to submit a detailed accounting of all its older pipelines that have not undergone high-pressure water testing, the inspection method best-suited for detecting flawed welds.
Meanwhile, state regulators are seeking to sanction PG&E for shoddy record-keeping in general and on its San Bruno line in particular. They gave the utility until Monday to say whether the record-keeping problems led to the disaster.
The weld that ruptured on the San Bruno line was a type known as DSAW, or double submerged arc welding. This involves completing welds from both the inside and the outside of the pipe, forming what appears to be an hourglass pattern, with the two welds merging at the center.
PG&E said federal rules and engineering standards consider such welds to be superior to other types and equivalent to seamless pipe.
The federal safety board’s metallurgists concluded the weld that ruptured in San Bruno was incomplete on the inside half of the hourglass pattern, suggesting that welders who put the pipeline together botched the job. The transmission line went in the ground in 1956 and apparently consisted of pipe that PG&E bought sometime after 1948, the company said.