It's called microbiologically influenced corrosion, also known as MIC. In a report released by the San Francisco Chronicle Friday morning, investigators will see if that may be a cause in the San Bruno explosion.
MIC is believed to be the cause of a deadly explosion in New Mexico, 10 years ago. A gasline ruptured in the desert, killing 12 people. After looking at the wrecked pipeline, investigators found destructive microbes, which can lie dormant and undetected for years, in an underground pipeline. Then without warning, can spring to life and start eating and corroding the metal. The pipeline in New Mexico was over 50-years-old, and 30 inches in diameter.
The pipeline in San Bruno that ruptured on September 9 was over 50-years-old and 30 inches in diameter.
According to the Chronicle, PG&E told state regulators last year that there was "ongoing concern" about the potential for internal corrosion, along the 46 mile pipeline, which ran from San Francisco, through San Bruno, down to Milpitas.
The sign of corrosion-causing microbes had shown up in several tests along the line. Experts, not associated with PG&E, confirm it's very likely pipelines, as old as 50-years-old, could have microbes in it.
The only way to check is by sending robots called smart pigs, or cleaning pigs, to detect any cracking in the walls, or to remove any gunk along the walls. But they don't fit into narrow pipelines, like the one in San Bruno.
A professor of civil engineering at USC disagrees to parts of the report, saying it's unlikely the cause is internal corrosion.
"If you look at the statistics of the U.S. Department of Transportation -- most of the cases of corrosions damage are external," said Dr. Jean-Pierre Bardet of USC's Civil Engineering Department.
PG&E can't comment at this time to the article because of the ongoing investigation, but will say MIC is rare in the pipeline system. There have been seven leaks in the PG&E transmission lines, about 6,400 miles, since January 2005 due to internal corrosion. But they don't know if they were caused by MIC specifically. The problems were repaired, the liquid inside removed, and microbial inhibitors applied when necessary.
The investigation into the cause of the San Bruno explosion is expected to take a year.