The focus of public speculation on the cause of Pacific Gas and Electric Co.'s (PG&E) Sept. 9 transmission pipeline explosion in San Bruno, CA, shifted last Friday inside the pipe to the possibility of corrosion-causing microbes that can go undetected within older gas pipelines. And on Monday news reports of PG&E's leak history caused the utility to issue a statement defending the thoroughness of its transmission pipeline maintenance and safety checks.

"On 'high-consequence area' pipelines [in populated and environmentally sensitive sectors] we report everything -- from a pinhole[-sized] leak to a third-party dig into the pipeline," a PG&E spokesperson said. "We continue to work with the [federal] PHMSA [Pipeline and Hazardous Materials Safety Administration] to determine how our self-imposed strict reporting can be improved."

The San Francisco-based combination utility was responding to a report in Monday's Los Angeles Times that cited PG&E for having the highest rate of leaks reported to PHMSA per 1,000 miles of pipelines in high-consequence areas during 2004 through 2009 (6.16 leaks average each year and 38 in total), compared to Sempra Energy's Southern California Gas Co. (SoCalGas), which averaged 2.22 leaks and 22 in total during the same period, according to the Times summary of PHMSA statistics.

For the period, the numbers published showed data for Florida Gas Transmission Co., Energy Transfer Co., Williams Gas Pipeline (Transcontinental Gas Pipe Line), Texas Eastern (Spectra Energy Corp.) and Natural Gas Pipeline Co. of America (Kinder Morgan), which collectively only reported seven leaks over the same period. PG&E and SoCalGas were shown to have 2,341 miles of transmission pipelines in high-consequence areas; each of the other pipeline operators listed has smaller amounts of pipe in these similar areas individually, but collectively they have more than 3,000 miles of pipeline in such areas.

PG&E said the Times report looked at "less than one-third" of the pipeline miles traversing the sensitive areas, and to be more accurate it should compare leak records from all of the pipelines in such areas, the utility spokesperson said.

Regarding the corrosion speculation that surfaced last Friday, PG&E spokespeople contacted late Friday by NGI verified the possibility that can be a cause but would not speak to the segment of pipe that failed in San Bruno.

Continuing work seeking to identify the cause goes on at the National Transportation Safety Board (NTSB), and as such, the local utility will not comment on potential causes, nor will NTSB at this point. Local news media surfaced the possibility of "microbiologically influenced corrosion" (MIC), and PG&E was forced to acknowledge that it had found one possible case in the past five years that showed it could have involved MIC.

"We have found a leak [on the 6,400-mile transmission pipeline system] in our post-repair surveys where we believe that favorable conditions existed for MIC to have been involved," a PG&E spokesperson said. That leak occurred in the past five years during which the utility experienced three transmission pipeline leaks.

The utility did not say in what part of its system the potential MIC internal corrosion could have taken place, nor would it confirm that MIC was automatically one of the potential causes that NTSB would analyze. "We really cannot speak to NTSB's investigation."

According to local news reports in the San Francisco Chronicle PG&E more than a year ago had told state regulators about its concern regarding internal corrosion developing in its 46-mile transmission pipeline between Milpitas, CA and San Francisco that included the segment in San Bruno that failed on Line 132. However, the combination utility would not confirm that for NGI.

A major interstate natural gas transmission pipeline that failed 10 years ago in New Mexico was more than 50 years old and the same 30-inch-diameter size when it ruptured, killing 12 people. Subsequently MIC was identified as a possible cause. The microbes lay dormant and cannot be easily detected externally until the small bacteria begin eating away the metal.

Two years after the New Mexico tragedy, NTSB was still investigating the cause of the fatal explosion. Earlier in mid-2002 the NTSB issued a series of factual reports that appeared to confirm federal investigators' initial suspicions of substantial internal corrosion as the cause. It found "severe corrosion damage" on the bottom of the interior of the 1950s-vintage pipeline near the explosion site (see Daily GPI, Aug. 30, 2002).

In February 2003 NTSB concluded that the probable cause of the fatal explosion and fire on one of El Paso's mainlines was "severe internal corrosion" of the 1950s-vintage line, which spans California, Arizona, New Mexico, Oklahoma, Texas and northern Mexico. The board cited the pipeline's inadequate corrosion-control program and lax oversight by the federal Office of Pipeline Safety inspectors as contributing factors, but it did not specify MIC as the internal culprit.

A full seven years after the incident, the Department of Justice and Department of Transportation and El Paso reached a settlement that required comprehensive reform of the interstate pipeline operator's entire 10,000-mile system and ordered El Paso to pay a multi-million-dollar civil penalty (see Daily GPI, July 27, 2007). It was the first judicial settlement brought under the Pipeline Safety Act, requiring El Paso to spend at least $86 million to enact widespread and comprehensive modifications to its pipeline system, with a focus on eliminating internal corrosion. At the time El Paso also was ordered to pay a $15.5 million civil penalty to resolve alleged violations.

The only way to check for MIC is to shut down portions of the transmission line, purge the line of any gas and run robotic smart pigs through the segment.

In regard to the PG&E pipeline failure, some engineering experts quoted by Bay Area news media that continue to cover this story very closely have said that most causes for major gas pipeline failures are found to be due to external causes -- not internal.

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