Pacific Gas and Electric Co. (PG&E) has told state regulators that at least 34 miles of natural gas transmission pipelines running through highly populated areas have been incorrectly identified as "seamless," similar to the section of 30-inch diameter pipe that ruptured in San Bruno, CA, last September.
The latest revelation was part of a letter from a PG&E utility manager to the California Public Utilities Commission (CPUC) and is part of the San Francisco-based combination utility's ongoing data-gathering and pipe testing effort unleashed when flawed record keeping was uncovered earlier in the year.
Bill Stock, PG&E director of regulatory relations, reportedly did not indicate where the 34 miles of high-pressure pipeline are located. It is part of the 152 miles of pipe in high-consequence areas (HCA) that was of the same vintage and had the same characteristics as the failed segment on PG&E's Line 132 in San Bruno that the utility in March committed to complete testing and/or replacement by the end of this year.
PG&E identified a separate 118 of the 152 miles of pipe that was 24- to 36-inch diameter and was installed prior to 1962, none of which had strength test records and that may have been manufactured by a certain company. Also in HCA areas, the 34 separate miles of pipe were "recorded (erroneously) as being pipe greater than 24-inch diameter and installed prior to 1974 that had no strength test records," PG&E said in its letter to the CPUC.
All of the pipe being focused on is double submerged arc welded, as was the segment that ruptured in San Bruno.
PG&E did not dwell on the 34 miles of misidentified pipe in its six-page letter, which also discusses replacements-vs.-hydrostatic tests; prioritization for hydrostatic testing; pipelines with lowered pressures; and an outline for the proposed hydrostatic testing process and the public safety considerations.
In its reply virtually the same day that PG&E sent its letter, the CPUC had a number of recommendations for the utility, such as addressing pipeline coatings among other pipeline aspects being tested, but it gave no reaction to the 34 miles of mistakenly identified "seamless" pipe.
"We ...support PG&E's objective of beginning the work to perform the testing expeditiously and recognize that PG&E is still be developing certain of the procedures and protocols that will apply to the program," said Deputy Energy Division Director Julie Halligan in a response letter to PG&E's Stock.
More recently, in an April 20 response to the CPUC to answer more questions, PG&E said it erred in telling the state regulators that a five-mile portion of Line 132 (mileposts 46.59 to 51.53) had not had its operating pressure dropped by 20% as did the rest of the transmission line because to do so would have created a high risk of outages to small, core customers to the north.
"A 20% reduction in pressure for this section of Line 132 will result in limiting the upstream pressure at Martin Station [in San Francisco] to the low 100 psig range [for maximum operating pressure] while the minimum system pressure into San Francisco must be maintained at a 90 to 110 psig range to meet demand."
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