A report in Sunday's San Francisco Chronicle based on a utility filing to state regulators earlier this year has raised doubts about the safety of Pacific Gas and Electric Co.'s (PG&E) natural gas pipeline system and the utility's nearly two-year effort to improve safety and reliability since the fatal San Bruno, CA, pipeline explosion.
PG&E's March report to the California Public Utilities Commission (CPUC) cites up to 239 potentially at-risk pipe segments that combined represent nearly 50 miles of pipeline. The segments at one time are thought to have had their pressures pushed above their legal limits, or the maximum allowable operating pressure.
The mayor of the suburb of Hillsborough on the San Francisco Peninsula adjacent to San Bruno expressed concerns about two existing gas transmission pipelines in the news accounts.
PG&E and consultant Kiefner and Associates Inc. put together an engineering critical assessment (ECA) that was the basis for the utility's immediate focus to determine if the potentially at-risk segments had been compromised by "unstable" manufacturing of the pipe or a problem created during pipeline construction.
"It should be noted that conservative assumptions were made during the ECA evaluation when data was not readily available," a PG&E spokesperson said. Thus, the ECA determination and subsequent action plan may be changed if PG&E's ongoing record search finds data that would confirm that the segment does not have problems due to manufacturing or pipeline construction flaws, he said.
The potentially troublesome segments include part of two pipelines running north to south along the peninsula south of San Francisco, specifically Lines 109 and Line 132, which is the one whose segment failed in San Bruno Sept. 9, 2010 with catastrophic consequences.
Segments are slated for testing, replacement or direct testing with smart interior equipment looking through the internal and external parts of each line. Identification of the potentially troubled segments came as part of the ECA.
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