The National Transportation Safety Board today released its preliminary report
on "Accident No. DCA10MP008"-- the San Bruno PG&E pipleline explosion and fire in plain English.
The brief document offers a telling glimpse as to how Sergeant Joe Friday would conduct a review of a massive inferno that engulfed an entire neighborhood. No, you won't find any damning assignments of blame heaped upon PG&E here -- but you do find a few interesting things.
- Prior to the blowout, an electrical interruption cut power to the regulating valve for the ill-fated Line 132. As a result, the valve moved from "partially open" to "full open." Still, the pressure of gas flowing through the pipe apparently never exceeded the safety limit of 400 pounds per square inch -- though it got awfully close.
- "The examination revealed that the ruptured segment was
27 feet 8 inches long at its longest length, and consisted of a pipe
section and four smaller pipe pieces (pups) between 3 feet 8.5 inches
and 3 feet 11 inches long (pups are numbered one through four from
south to north)."
The following laboratory work on the pipe has been completed:
- Written documentation, photo documentation and visual inspection of the pipe.
- Removal of the asphalt coating from outside of the three pipe segments in preparation for non-destructive examination work.
- Radiography of the girth welds and select seams.
- Microbiological testing of the pipe surface (samples currently being analyzed).
- Ultrasonic wall thickness measurements.
- Magnetic particle inspection of welds and seams.
- 3-D laser scanning of the pipe pieces for a digital dimensional record of the evidence.
- Measurement of the longitudinal and circumferential pup dimensions.
- Removal of key fracture surfaces from the ruptured segment for
further laboratory examination at the NTSB materials lab in Washington.
The following additional work is currently ongoing:
- Precision cleaning of the fracture surfaces on the pieces cut from the ruptured pipe segment.
- Hardness and microhardness testing.
- Optical fractographic analysis and photodocumentation of the
fracture surfaces on the pieces cut from the ruptured pipe segment.
- Preliminary scanning electron microscopy of the fracture surfaces on the pieces cut from the ruptured pipe segment
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