PG&E received orders on Wednesday to reduce pressure on four of its natural gas transmission lines, which investigators discovered were running above maximum pressure levels in the Bay Area and Central Valley, according to officials.
Pressure on lines running through Milpitas, San Jose, Watsonville, and the Aptos Hills was deemed unsafe by investigation results released Wednesday by the California Public Utilities Commission.
Officials called for the investigation after an explosion of a pipeline segment tore through San Bruno’s Crestmoor Canyon neighborhood on Sept. 9, killing eight people and destroying or damaging more than 38 homes.
The CPUC learned this week that in the years leading up to the explosion, the four transmission lines and perhaps others were running above the state law’s maximum allowable operating pressure, or MAOP.
“We are being particularly cautious and ordering the pressure reductions until we can better understand the safest operating pressure on those pipelines,” CPUC Executive Director Paul Clanon said in a statement.
More than 12 miles of pipeline in the Bay Area and another 17 miles of pipeline in Central Valley have been ordered to have pressure reduced by 20 percent below their MAOP.
In a response to the CPUC’s orders, PG&E officials revealed that a pipeline running from Milpitas to San Jose had its pressure running up to 100 pounds per square inch over its MAOP limit between 2008 and 2010.
“There are times when the pressure on a pipeline may operate outside of the specified limits,” a letter from PG&E said.
Lines run above pressure because of equipment failure, liquid contamination or human error, according to PG&E.
The line running under Watsonville was running 35 pounds per square inch above its MAOP in 2009, the letter said.
The investigation revealed a total of 16 transmission lines throughout California were running above their MAOP. But in eight of the cases, the pressure was over by “just a few pounds,” a PG&E spokesman said.
“In all cases, PG&E restored the lines to normal operating pressure, inspected the lines, and made repairs as needed and surveyed the lines for leaks,” spokesman Paul Moreno said.
Moreno couldn’t say when the pressure on the four lines would be reduced, but he said the reduction shouldn’t impact service to PG&E customers during winter months.
“We don’t think service will change given the given typical weather patterns,” he said. “If we need to, we’ll be in touch with the CPUC.”
In addition to reducing pressure on the four ordered lines, the CPUC ordered PG&E to reduce the operating pressure on any other transmission lines that have segments located in high consequence areas, or densely populated areas that are difficult to evacuate in emergencies, like the San Bruno neighborhood.
The CPUC also ordered an extensive investigation into PG&E records after officials discovered the company misrepresented the kind of pipeline that was under the San Bruno neighborhood before it exploded.
Line 132, which was installed under the Crestmoor Canyon neighborhood in 1956, was initially believed to be “seamless,” according to PG&E, and not made of welded parts.
But a metallurgical report released on Jan. 21 said a weld on the pipe had “overstress from the root of the weld.”
Rep. Jackie Speier, D-San Mateo, said she was profoundly disturbed by what she read in the Jan. 21 report.
“Over the past several months, experts have told me that welding flaws are detectable,” she said in a statement.
She said that PG&E believed the pipe was seamless and its crews “never once inspected the condition of the welds.”
There had been reports by San Bruno residents that there was a natural gas smell in the neighborhood before the explosion, which could have indicated that the pipeline was leaking before it ruptured.
But the NTSB found in a December report that there was no physical evidence of a pre-existing leak in any of the ruptured pipe pieces.
The December report found that the ruptured piece of pipe showed no evidence of corrosion, and no dents or damage that could have been inflicted during construction.
Saul Sugarman, Bay City News
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