In a report released Tuesday, Pacific Gas and Electric Co. (PG&E) said since the end of October, when it issued an initial report, it has confirmed an additional 21 "Grade 1" leaks on its system, bringing the total number of leaks that required immediate action to 59, all of which have been repaired.
The utility's accelerated leak survey of all of its gas transmission pipelines was launched last September in the wake of the rupture and explosion of one of its pipelines in San Bruno, CA (see Daily GPI, Jan. 27).
PG&E said it responded promptly in all 59 cases where it discovered a leak that created a potential hazard. For other indications of nonhazardous leaks, PG&E scheduled further investigation or repairs in accord with industry standards, it said.
A study by third-party consultants hired by the utility concluded that PG&E leak rates and reporting practices compare favorably with the rest of the industry, the utility said. It also provided a progress report to the California Public Utilities Commission (CPUC) on its program to review and validate about 1.25 million records pertaining to 1,800 miles of gas transmission lines in populated areas.
"These reports reflect our ongoing efforts to raise the bar on our performance and effectively address any and all public safety issues on our gas system," said Kirk Johnson, vice president of gas engineering and operations. "We know that transparency is vital both to regaining public confidence and to ensuring that we and the industry learn the right lessons from the San Bruno tragedy and act on them appropriately."
According to the latest report, eight of the additional 21 Grade 1 leaks not previously reported were on transmission facilities. The remaining 13 were on either gathering facilities or distribution facilities.
"Equipment-related leaks were the leading cause of leaks repaired as part of this accelerated leak survey," the report said. "Equipment leaks occur on transmission appurtenances and include failures at threaded components, gaskets, valve packing, etc. PG&E found that most of these equipment leaks were associated with PG&E high-pressure regulator (HPR) sets serving one to two customers and on facilities generally less than 1 inch in diameter.
"The next highest cause of leaks fell within the category 'other.' These are leaks where PG&E performed an immediate response and repaired the leak by tightening, lubricating or adjusting. The 16 leaks identified in this category could have been considered equipment leaks as they are associated with thread and lubrication components failure. These leaks are also ones that...may not even have been reportable in the first place."
Based on findings from the leak survey, PG&E said it plans four enhancements to its program, including stepping up its leak repair schedules and evaluating the merits of helicopter-based laser leak detection systems.
To accompany the survey, PG&E hired third-party consultants ViaData LP and Oleksa and Associates to evaluate leak reporting practices and compare PG&E's results to the industry. The firm's analysis concluded that:
In another report to the CPUC, PG&E said it is collecting, scanning and indexing about 1.25 million records relating to its transmission pipelines.
PG&E said that over the next six weeks it expects to determine the pipeline segments for which it has complete, verifiable and traceable records of prior pressure tests. It said it will perform excavations to verify pipeline features where necessary. The data is expected to help verify the safe maximum operating pressures on transmission pipelines in populated areas.
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