This explosion took place September 9, 2010, the writer prepared a post on this blog at that time. It caused a massive crater, killed eight people and destroyed 37 homes. A 30-foot length of the 30" diameter, 3/8 " wall thickness elevated into the air and fell some 100 feet away. The weekend edition of the WSJ for January 22-23, 2011 had a short article on page A3.The title, "Pipeline-Blast Probe Finds Welding Flaws" pretty much summarizes the finding so far. The NTSB hopes to issue a final report that lays out the causes of the blast after it conducts hearing in Washington DC, during the first 3 days of March, 2011.
Problems identified in the pipeline, built in 1948 by PG&E Corp., included welds that used insufficient welding material and those in which metal wasn't properly fused (weld penetration). The utility continues to operate the remainder of the main at 20% below maximum allowable pressures to provide an additional safety margin. The investigation has uncovered discrepancies between the types of pipe that records suggested were in the area and the actual pipes found there—(undocumented substitutions?). Investigators discovered lengthwise welds, as well as many small pieces of pipe welded together.
Lengthwise welds are required for conical transitions between different diameters. Corrosion is claimed NOT to be a factor. Also the utility's records said the pipeline was made of seamless pipe, implying there would not be lengthwise weld seams.
To this writer's mind there has been no explanation of how the explosion occurred UNDER the 30-foot section and blew it high enough above the ground to land some 100 feet away. Logic says there had to be a sizeable cavity UNDER the section that somehow became filled with a mixture of about 5% NG and air to such pressure the required explosive force WAS generated. But so far no mention of such cavity possibility.
Interesting
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