Under more public scrutiny in the wake of the devastating failure of a high-pressure transmission pipeline segment in San Bruno, CA, Pacific Gas and Electric Co. (PG&E) has made public its maintenance/inspection prioritization, but it gives no sense of how it has been identifying and dealing with high-risk portions of the 6,438 miles of transmission pipelines in its system.
While the San Francisco-based combination utility said Thursday its top executives have met with local government officials and fire departments in San Bruno, the city and county of San Francisco and just about all of the suburbs found along the pipeline on which the failure occurred (Line 132), PG&E is not adding more detail to the Top-100 listing of preventive pipeline maintenance.
In dissecting what was made public, only one project had been indicated as completed and five more as either in the engineering/planning or construction phases. The vast number of segments and projects involving more than 90 pipeline segments were either at one of the two earliest levels of attention: “monitoring” (4 projects involving 22 segments) or “initiated” (37 projects involving 72 segments).
Monitoring refers to utility engineers “monitoring and reviewing line segments to see if they need to be addressed in projects.” And the term “initiated” means that engineers have determined those segments need further study and analysis.
Part of the new independent state investigation ordered by the California Public Utilities Commission (CPUC) will examine whether there are “systemic management problems at the utility and whether greater resources are needed for fundamental infrastructure improvements — not only for the PG&E system but elsewhere in California,” according to CPUC President Michael Peevey.
PG&E’s backbone transmission pipeline system has 20,000 segments, typically defined as lengths of pipe located between two valves that control flow and pressure. Segments range in size from four to 42 inches in diameter.
The pipelines typically operate at pressures between 100 and 1,040 psig (pounds per square inch gauge), the utility said. Pressures depend on the size and physical characteristics of the pipelines. Federal limits for transmission pipelines such as Line 132 are set at 400 psi, and PG&E has used 375 psi as its operating limit. Since San Bruno it has lowered pressures in the San Bruno area to 300 psi.
In addition to the ill-fated Line 132, three other transmission pipelines serving the peninsula region south of San Francisco have been reduced to 300 psi — Lines 100, 101 and 109 — a PG&E utility spokesperson told NGI last Wednesday.
Some industry stakeholders have raised the question of how long PG&E can operate at the lower pressures, especially as the weather gets colder, without having to curtail some of its large interruptible customers. NGI raised that and other operating questions with a utility spokesperson,but did not get an immediate response.
“Hundreds of automatic over-pressure control valves, installed where appropriate in the transmission system, protect pipelines from exceeding their maximum pressure design limits,” PG&E said in a description of its backbone system. Gas supplies fed northerly through the three transmission pipelines traversing the peninsula are fed from Milpitas in the far southeast part of the San Francisco Bay. Those supplies can originate from storage, Canada, the Rockies or the Southwest, all of which have connections to PG&E’s system.
The transmission pipeline system is dotted with sensors that feed information about pressure, flow rates and other operating information to the PG&E gas control center in San Francisco. The utility has said the control center has the capability to shut down certain pipeline systems via remote control. The segment that failed in San Bruno did not have this remote shutdown capability, and it took utility field personnel an hour and 46 minutes to manually shut off the flow of gas in Line 132 immediately following the explosion.
“While the National Transportation Safety Board conducts its investigation into the cause, we must do our part to examine our own regulatory processes, shore them up where necessary and restore public confidence in our utilities’ infrastructure,” said CPUC Commissioner Timothy Alan Simon, the lead California regulator on natural gas issues. Simon suggested that additional investigative work may be needed by the CPUC and the state legislature in addition to the independent review panel that the state commission created Thursday (see Daily GPI, Sept. 23).
“As a public agency, we must restore confidence by keeping all options on the table,” said Simon, noting that in 2007 he was the assigned commissioner on PG&E’s last completed gas transmission/storage rate case (Gas Accord 4), covering the 2008-2010 period. He is heading the oversight of PG&E’s pending gas transmission/storage settlement for 2011-2014.
Within days of the disaster in San Bruno, Simon and CPUC Administrative Law Judge John Wong issued a ruling asking parties to respond to questions about whether the settlement is still applicable given the failure of Line 132. “Does that settlement provide sufficient funds to complete a thorough safety inspection of PG&E’s entire gas transmission pipeline system during this four-year period, and has PG&E appropriately prioritized the pipeline safety, integrity and reliability work that the utility will be performing during this period?”
Those are questions neither the utility, nor the regulators, have answered publicly yet.
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