California regulators last Thursday gave Pacific Gas and Electric Co. (PG&E) approval to begin lifting pressure restrictions on some major natural gas transmission pipelines in the wake of last year’s San Bruno pipeline rupture and explosion.

PG&E now can reset new maximum operating pressures (MOP) on certain pipeline segments important to the combination utility maintaining adequate capacity to serve winter heating and power generation loads, the California Public Utilities Commission (CPUC) said.

The restrictions were imposed by the CPUC days after the Sept. 9, 2010 pipeline explosion. A regulatory commission hearing was held last month on the PG&E request to increase MOP to 365 psig on three pipelines (Lines 101, 132A and 147).

By its action Thursday, the CPUC authorized the pressures on all three pipeline segments to be raised no higher than the 365 psig level. The authorization covers all of Line 101 running 34 miles up the west side of San Francisco Bay from Milpitas on the south and to San Francisco gas load center on the north, and two shorter cross-tie pipelines: the 1.5-mile link of 132A between Lines 101 and 109; and 3.8-mile link between Lines 101, 109 and 132.

PG&E said it will raise the pressure in these three pipeline links beginning Monday, which would effectively put its natural gas system operations on the San Francisco peninsula back to its normal operating pressures for the first time since the explosion. “Restoring pressure will help provide PG&E customers in San Francisco and San Mateo counties with adequate gas service during the cold months ahead,” the utility said.

Both the CPUC and utility reiterated that in the past 14 months PG&E has verified the safety of these pipelines through a program that included pressure tests, records verification and visual inspections. In some instances segments of pipe were replaced.

“We used a thorough process to verify the integrity of these lines, and we’re confident that they can be restored to deliver gas to our customers’ homes and businesses safely and reliably,” said Kirk Johnson, vice president for gas transmission, maintenance and construction.

Noting that the CPUC Consumer Protection and Safety Division recommended that the MOPs be restored after reviewing all of the utility’s testing/verification work, CPUC Commissioner Mike Florio said the state regulatory commission is now satisfied that PG&E has “demonstrated that the pipelines in question can be safely operated at the increased MOP.” Ultimately, he said, it is PG&E’s “duty to furnish and maintain safe equipment and facilities.”

In early November PG&E said its first test failure and pipeline segment replacement was completed on a portion of the major transmission pipeline bringing supplies from the Southwest at the California-Arizona border to load centers in the central and northern parts of the state (see NGI, Nov. 7).

Aside from the single failed test, at the time PG&E said it had verified 125 of 152 miles of transmission pipeline that were designated as top priority for safety verification work. Those 125 miles were either successfully hydrostatically tested and tied in, successfully tested but not yet tied in, replaced, or had strength test pressure records verified.

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