WASHINGTON—PG&E’s methods for testing Line 132 were not the best for inspecting defects in the pipeline, and there could perhaps not yet be any technology available that could detect all possible problems with gas transmission lines, officials said today on the last day of the NTSB hearings on the Sept. 9 gas pipeline explosion in San Bruno.
Since 2003, Pacific Gas & Electric Co. has used a method called direct assessment to examine the risks associated with its natural gas pipelines. In fact, the last time PG&E inspected Line 132—the pipeline that exploded in the Crestmoor neighborhood, leaving eight people dead—the after crews checked it for leaks several times and even dug it up in three places.
But when National Transportation Safety Board investigators questioned pipeline industry officials about the effectiveness of using direct assessment to detect potential hazards in gas transmission lines, one official said the method—and others that many pipeline operators use—often results in flaws.
As the NTSB begins to hone in on a in Line 132 as a possible source of the explosion, investigators turned their attention today to what tools might be best used to prevent a disaster such as the Crestmoor fire from happening again elsewhere.
Several pipeline officials explained how a number of pipeline operators in other parts of the country used —robotic devices used to detect the physical condition of a pipeline—or hydrostatic testing to inspect their lines, with both methods having varying amounts of success.
Several officials explained that smart pigs are usually only good at detecting corrosion but not other defects, and they require pipelines to be built to allow the robotic devices to maneuver throughout them. Only about 20 percent of PG&E’s gas transmission lines are “piggable.”
Hydrostatic testing, in which water is flushed through a pipeline to determine cracks, also isn’t completely fail-safe, the pipeline officials said.
While experts say the method is more effective than direct assessment, the water tests require operators to shut down service—a risk many utilities aren’t willing to take.
Noting that it appears the failure of Line 132 originated from a faulty weld inside the pipe, NTSB investigator Frank Zakar asked a pipeline official whether any better inspection tool existed that could have detected a flaw in the gas transmission line.
“Yes, there is,” said Geoff Foreman, an industry engineer for General Electric Co.
When asked to describe the tool, Foreman said the best inspection tool is called an electro-magnetic acoustic transducer, or EMAT, a type of smart pig that has been used for years in the liquid gas industry to detect cracks in pipes.
But even that method might not be completely feasible at this point, Foreman said, because GE is still building the prototype that could be used to inspect natural gas transmission lines.
Offering a conclusion on which method is best for inspecting pipelines, Charles Dippo, the vice president of South Jersey Gas Co. and the American Gas Association, said no method offers a panacea.
“There is no single silver bullet,” Dippo told investigators.
After the hearing, Deborah Hersman, chairwoman of the NTSB, said the information provided today about the issues with pipeline inspections was vast in scope.
But she was concerned about whether the findings presented over the three-day hearing this week would be heeded by the pipeline industry, especially when this isn’t the first time the NTSB has investigated a gas pipeline explosion.
“One of my concerns is to ensure that lessons learned in the past and regulations that exist are complied with,” Hersman said. “We don’t ever want to investigate another accident like what happened in San Bruno."
