Welding procedures and pipelines

The ongoing investigation in the San Bruno natural gas pipeline rupture by the NTSB has revealed that while 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 pipeline was erected in 1956 and the standards at that time are being looked into. As 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."
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