Rail defect likely behind last week’s BART problems

Major delays in and out of San Francisco occurred after the discovery of a 10-inch section of broken rail between the Civic Center and 16th St. Mission stations. There are no reports of any injuries due to the break, and an investigation is underway into why the section of track failed. less Major delays in and out of San Francisco occurred after the discovery of a 10-inch section of broken rail between the Civic Center and 16th St. Mission stations. There are no reports of any injuries due to the ... more Photo: Courtesy Of BART Photo: Courtesy Of BART Image 1 of / 13 Caption Close Rail defect likely behind last week’s BART problems 1 / 13 Back to Gallery

A manufacturing defect in a 10-inch section of BART track may have triggered last week’s rail fracture, which led to systemwide service delays and one of the most frustrating days for commuters in recent memory.

Hydrogen bubbles were found in the rail segment that broke between the 16th Street Mission and Civic Center stations in San Francisco, BART officials said Friday. The presence of the bubbles near the surface of the rail — most likely trapped there during the manufacturing process — could have weakened the line and caused it to snap, officials said.

Further tests still need to be done to confirm that the production defect is the source of the problem, said BART spokeswoman Alicia Trost.

“Obviously, we need to find all the rail we got in 2011 and test it to make sure it doesn’t have hydrogen bubbles at the surface as well,” Trost said.

The problem with the rail line became apparent about 9:20 a.m. May 6 when an East Bay-bound train operator reported an unusually bumpy ride between the San Francisco stations. BART immediately shut down the track and dispatched an inspection team, which discovered a 10-inch gap in one of the rails.

In San Francisco, trains had to share a single track while repair crews removed the damaged section of the rail and installed a new piece as a temporary fix. Service was stalled for more than six hours systemwide.

Inspectors discovered that BART workers had failed to remove “slag” or excess metal underneath the rail during welding work in 2011. While the excess metal did not cause the break, Trost said, it could have prevented inspectors from discovering signs of a manufacturing flaw.

“This is a good example of why you should knock it off and grind it rather than leave it hanging there,” Paul Oversier, BART’s assistant general manager for operations, told BART directors at a board meeting Thursday. “The fact of the matter is that it’s not a best practice to do welding and just leave the excess metal, even though it’s under the rail, it’s not impacting operations in any way.”

While stressing that the excess metal did not cause the break, Oversier said, “It’s just bad housekeeping, and this is an example of why bad housekeeping can come back and possibly bite you.”

The rail section that broke was installed in 2011, and recent metallurgical tests showed that it “was in good shape,” Oversier said. “So it wasn’t a case of worn rail.”

It wasn’t immediately clear if the recent testing could or should have detected a production defect.

Oversier acknowledged that although outside inspectors had discovered the excess-metal issue in September, BART officials did not learn about it until after they contacted the company about last week’s disruption.

Henry K. Lee is a San Francisco Chronicle staff writer. E-mail: hlee@sfchronicle.com Twitter: @henryklee