WASHINGTON ? The natural gas pipe that burst in San Bruno, Calif., on Sept. 9, killing nine people and destroying nearly 40 houses, had numerous flaws in its welds, the National Transportation Safety Board said in a report released Friday.
The board noted previously that utility records said the pipe was seamless, but that when excavated, it proved to have welded seams.
The board issued what it called a factual report, without any analysis, and the report did not say whether the maximum pressure that the welded pipe could contain was lower than what the utility, Pacific Gas & Electric, believed. But it also announced that a hearing scheduled for March to discuss issues raised by the accident would extend for three days, not the two days previously scheduled.
Welds on the seams running the length of the pipe segments showed ?various defects,? the report said. Some welds were porous and in some cases the weld material did not fill all the space it was supposed to, or fusion of the weld material with the pipe was incomplete.
In addition, the pipe was supposed to be coated to protect it underground, but big areas had no coating, the engineers found. But, the board said, there was no sign that the accident was caused by corrosion.
Flaws were also found in the girth welds, the ones that connect segments of pipe.
The pipe, 30 inches in diameter, buried three feet underground, was installed in
1948. Welding standards have been tightened since then, the report noted.Another issue for the investigators is how high the pressure rose in the pipe just before the rupture. Just before the accident, Pacific Gas & Electric technicians inadvertently cut power to a computer system, and that triggered a valve to open, causing pressure to rise. The pressure measurements were reported by the same computer system. Pacific Gas said that the pressure did not rise above the levels it believed the pipe could handle, but the accuracy of the measurements themselves is also under investigation.