Williams Gas Co. works to prevent another rupture

Special Report: Appomattox Pipeline Explosion

• More stories on the pipeline explosion
• Aerial photos of the site one year ago and now
• 911 recordings from the day of the explosion
• Maps of pipeline incidents across the U.S.

A year later, investigators for both a federal oversight agency and Williams Gas Company say they have answers to two key questions related to the natural gas explosion:

- What caused it?

- How can a similar rupture be prevented?

Larry Hjalmarson, vice president of operations at Williams, said the problem was twofold — corrosion controls failed to properly protect the pipe, and tools designed to spot corrosion failed to mark it as a critical repair.

The U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration cited the company last month for inadequate corrosion control at the failure site.

“The Notice of Probable Violation says we believe that the company had the information it needed to act,” said Jeffrey Weise, the agency’s associate administrator of pipeline safety.

“It fell apart because the company didn’t act fast enough. They were en route to address the issues, but not at the speed at which we believe they should have been moving. They had multiple indicators they had a problem.”

Both Williams and the federal investigation discovered that the rupture was caused by external corrosion that thinned the pipeline walls by 50 to 75 percent, rendering it unable to withstand the pressure pushing gas up the line. Corrosive soil, warm gas temperatures and a failing asphalt coating all contributed.

The company was fined partially for its cathodic protection — a light electrical current applied to the pipeline to force corrosion away from the line.

The company tested corrosion control at the site in 2003, which indicated a problem. Williams made improvements, tested again and made more improvements in 2006. A third test was not performed, which Hjalmarson said would have been more than federal regulations required.

Based on the tests Williams performed, he said the protections appeared adequate. The company now knows they weren’t.

“It did corrode and it did fail. … We tested again and we thought we had it under control. We didn’t.”

Investigators learned that the bedrock shielded the pipe from the cathodic protection system, Hjalmarson said.

Also, the way the pipeline corroded presented its own problem, he said. An inline inspection tool detected an anomaly but did not consider it an immediate concern. The profile was unusual — a smooth, gradual thinning of the pipe walls.

“The corrosion is usually a rugged, rough surface with dents and scratches,” Hjalmarson said. “I asked (other pipeline companies) if they had encountered that and they hadn’t. It’s an unusual type of failure.”

Using a portion of the pipe that failed, Williams is working with General Electric, the manufacturers of the inspection tool, to design a tool that better detects this type of anomaly. The company also is sharing whatever it has learned from the Appomattox incident with other pipeline companies.

Following the rupture, Williams inspected its Virginia lines, looking for the same signature in other areas. Workers also unearthed some pipelines, based on previous inspections, to see if anything was missed. Nothing has emerged thus far.

“I don’t want people to feel worried about our pipeline,” Hjalmarson said. “We want people to be confident in us. We know their confidence is shaken and it will take years, decades to restore that.

“People were frightened and the only way to fix it is years of safe operation.”