The US NTSB has released some further information on their investigation of the San Bruno disaster.
It’s notable mostly for the causes of failure that it eliminates. They appear to have ruled out external corrosion and excavation damage. They don’t speculate on what the causes might have been but merely note that the investigation is still in its early stages. Nevertheless there are some hints in both the text and one of the photos that they are looking at welds in the pipe, mainly the longitudinal welds.
It’s pleasing to see that the investigation will be very wide ranging, including “… pipeline control and operations, regulation and oversight, human performance, survival factors, and pipeline maintenance and records”. I think it will be many months before they reach a final position.