Two days after a portion ruptured in a hydrostatic pressure test, replacement work was completed Wednesday on a one-mile segment of Pacific Gas and Electric Co.’s (PG&E) 34-inch diameter transmission pipeline (Line 300B) that is part of a link to southwestern supply basins.

A PG&E spokesperson said the San Francisco-based combination utility had completed repairs on a segment of Line 300B in Bakersfield, CA, after a hydrostatic pressure test on Monday revealed a weakness on that segment (see Daily GPI, Oct. 26).

“Crews will be on-site tomorrow [Thursday] morning in Bakersfield to conduct another hydrostatic pressure test to confirm that this new section of pipe meets our standards,” the spokesperson said. The tests are part of a broader, long-term effort by PG&E, involving hydrostatic pressure testing on 150 miles of pipeline throughout its service area to help ensure that its (6,000-mile) natural gas transmission system is operating safely and reliably for its customers.

Monday’s rupture was the first failure experienced since PG&E began the hydrostatic testing program at the behest of state regulators earlier this year (see Daily GPI, May 5).

Hydrostatic pressure testing involves filling a section of pipe with water, pressurizing it to a much higher level than the pipe will ever operate with natural gas, then monitoring the pipe for at least eight hours. PG&E made available a video of the hydrostatic testing process.

“These tests are designed to identify any weaknesses in the pipeline, and any pipe sections that do not pass the test will be replaced,” the spokesperson said. Following a successful test, the section of pipe is emptied of water, dried thoroughly and placed back in service. A successful test would validate the safe operating pressure of the pipeline. PG&E said it would provide updates on progress as hydrostatic testing work proceeds.

On Monday, the failure occurred in a pipe section operated at 757 psig, which was installed in 1950. A double submerged arc-welded longitudinal seam failed during the test, the utility said. At the time of failure, the test pressure on the segment was 998 psig, which is 94.9% of the pipeline’s specified minimum yield strength. Crews had planned to pressurize the section up to 1,040 psig.

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