The smell of natural gas wafted across a portion of California's Silicon Valley Tuesday, and it was a welcome presence for a change for the utility and local officials, signifying that Pacific Gas and Electric Co. (PG&E) was moving forward to pressure test more of its gas transmission pipeline system that has been placed under close scrutiny since the pipeline rupture in San Bruno that killed eight people Sept. 9.
After encountering repeated criticism on its response to federal and state regulators to assure that all of its pipelines in highly populated areas are operating at pressures previously verified as safe (see Daily GPI, April 1), PG&E started on what it calls a "rigorous schedule" to test key parts of its transmission pipeline system that have similarities in size, location and operating conditions to the 30-inch diameter welded section in San Bruno that failed, causing an explosion and fire.
PG&E performed hydrostatic pressure tests on sections of pipe in Mountain View in the Silicon Valley and Antioch in the upper East San Francisco Bay on Tuesday, carrying out both pressure tests and camera inspections, a utility spokesperson told NGI. This work requires a lot of advance planning and notification of the local communities, requiring local work permits and coordination with local agencies. Gas is rerouted and continues to flow to homes and businesses throughout the testing.
In the immediate area of the tests, natural gas is provided to customers from another source on a temporary basis. The sections of pipe tested are removed from service and vented of all gas in a manner that PG&E emphasized is safe and controlled. The inside of the pipe is mechanically cleaned before the testing.
After the pipe section is purged of natural gas to allow the crews to work safely, the smell of gas can be noticeable to nearby homes or businesses, along with a loud sound made by the equipment that forces air through the pipeline, depending on the wind direction and weather conditions, the spokesperson said.
Sealed at both ends, the pipe section is filled completely with water and pressurized to a level that is specifically greater than the line's normal operating pressure. The test pressure is maintained and monitored for a set time period, typically eight hours, the spokesperson said. If the pipeline section fails the test, it is replaced immediately after the testing.
As part of its transparency efforts mandated by the California Public Utilities Commission, PG&E plans to send out regular updates on this and similar work in other communities. The spokesperson, however, noted that dates and activities are "subject to change."
PG&E plans to send a letter to customers in the San Bruno/South San Francisco area explaining its plans for upcoming hydrostatic pressure tests and camera inspection work through the inside of the pipe sections. Crews and equipment most likely will be mobilized in the area next week, the spokesperson said.
"In the coming weeks, we will be hosting open houses in both San Bruno and South San Francisco to further describe the work that we will be doing in their community," the spokesperson said.
"In each case, when the testing is completed, we will close and seal the pipeline and then restore the excavation sites. In order to return the pipeline to full service, we will purge the line to remove air from inside the pipe, and at this point, there is a second chance of a natural gas odor and a loud noise from the work site. As part of our standard protocol, we will be notifying the appropriate local agencies, including local cities and fire and police departments."
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