Safety and outage risks would climb dramatically if added pressure reductions are implemented on parts of the Pacific Gas and Electric Co. (PG&E) natural gas transmission pipeline system, the utility told the California Public Utilities Commission (CPUC) as part of an ongoing state proceeding following last September’s fatal pipeline rupture in San Bruno, CA, 10 miles south of San Francisco.

An administrative law judge’s (ALJ) proposed decision calls for all transmission pipelines in the state to be pressure tested or replaced if there is insufficient data supporting their current operating pressures (see NGI, May 16). Depending on the outcome of this proposed decision when it comes before the five-member CPUC next month, the call for reducing operating pressures may change, PG&E mentioned in its filing.

Proposals to lower pressures in parts of the PG&E backbone and local transmission pipelines “could result in adverse operational, safety and customer service impacts,” the San Francisco-based combination utility said. Thus, PG&E said it “advises against adoption of blanket 20% pressure reductions.”

Further, the utility’s in-house analysis indicates that pressure drops of 5-15% on the local transmission system, with or without corresponding drops in pressure on the backbone system, would similarly result in what PG&E called “significantly increased curtailment of noncore customers, including power plants and hospitals, and could limit [the utility’s] ability to inject storage for the coming winter period.”

“The CPUC will need to carefully balance a number of site- and condition-specific safety and operational factors in determining the need for additional pressure reductions on the PG&E system,” the utility told the state regulators, adding that the issue should be addressed in the implementation plans now being called for in the May 10 ALJ’s proposed decision.

PG&E has concluded that even pressure drops as low as 5% can have significant impacts, such as on its Baja Path (Lines 300A and 300B) where capacity would be cut 11% from 1,055 MMcf/d to 937 MMcf/d. The reduction in storage injection capacity would be about 1%, but the inventory swing would be reduced by about 16%, the utility filing said.

In analyzing 77 pipeline subsystems and the impact of 5%, 10% and 15% pressure reductions, PG&E concluded that 16 subsystems would not meet design standards at the 5% reduction level, but that grows threefold at 10% with 48 not meeting design standards, and it grows to 57 of the 77 subsystems with pressure reductions at the 15% level.

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