TransCanada Corp.’s new Bison natural gas transmission pipeline from southeast Wyoming to an interconnection with Northern Border Pipeline in North Dakota will remain out of service for a still-indefinite period as the company and federal regulators seek more answers surrounding a rupture in the first 17-mile leg out of the Powder River Basin in the southeast part of Wyoming.
Bison has been shut in with scheduled volumes from the Buffalo, WY, receipt point cut to zero since the July 20 rupture of the six-month-old pipeline in Campbell County, WY. According to local press reports, the incident could be heard 30 miles away (see Daily GPI, July 26), but it was in a rural area with the nearest farmhouse a mile away.
From the start, TransCanada has been speculating that the failed pipe segment had been hit by something externally, and the federal Pipeline and Hazardous Materials Safety Administration (PHMSA) has called for more testing before Bison can begin to be restarted.
On Tuesday a Houston-based TransCanada spokesperson told NGI the pipeline operator does not know when Bison will return to service.
A preliminary investigation into the cause of the rupture determined that it was the result of mechanical damage from something striking the pipe, TransCanada said last month. But testing and PHMSA’s own work on the cause continue.
“The affected pipe has been sent to the lab for various tests,” said TransCanada’s spokesperson, adding that it will be “some time before we get answers as to why this particular pipe failed.”
Earlier, the spokesperson had acknowledged that the failed segment was part of pipeline in Wyoming that was thicker than the rest of the 302-mile, 30-inch diameter pipeline and had been supplied by one of Bison’s shippers. It also operated at 72% of specified minimum yield strength (SMYS), compared to the rest of Bison that operates at 80% SMYS.
Subsequently, PHMSA has ordered TransCanada to conduct what the spokesperson called “some digs” along the pipeline to make visual inspections prior to the line going back into operation. “We also are doing inline inspections to conduct a magnetic flux leakage survey for the entire pipeline,” the spokesperson said.
“[We] and PHMSA both want assurance that we can operate this pipe safely before it goes back into service.”
Bison entered service on Jan. 14, transporting gas from the Powder River Basin to the Midwest. The pipeline extends northeasterly from the Dead Horse Region near Gillette, WY, through southeastern Montana and southwestern North Dakota where it interconnects with Northern Border’s system near that pipeline’s Compressor Station No. 6 in Morton County, ND. Bison’s design capacity is 477 MMcf/d.
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