Flaw in pipe a key factor in explosion: report

BUICK, B.C. (Canadian OH&S News)

A report released on June 4 by the Transportation Safety Board of Canada (TSB) has fingered a pre-existing flaw in a pipe as the primary cause of a pipeline explosion that occurred last summer near Buick, British Columbia.

The investigation found that certain types of pipe — welded using a low-frequency electric resistance welding technique — have a higher likelihood for defects such as cracks, which increases the risk of failure.

On 28 June, 2012, gas escaping from Westcoast Energy Inc.’s 16-inch Nig Creek pipeline ignited and the resulting fire spread to the surrounding forested area. The pipeline is part of Westcoast Energy Inc.’s sour gas gathering system in northern British Columbia. About half an hour later, the 6.625-inch Bonavista Energy Corporation pipeline — located three meters away in the same right-of-way— ruptured due to its exposure to the fire, causing another explosion.

 The situation was compounded by multiple inputs and alarms relating to other events, causing the specific alarms that followed the rupture not being responded to in a timely manner. “If excessive workload of system controllers is not properly managed, there is a risk that emergency response will be delayed,” the report suggests.

A laboratory analysis of the failed sections of the Nig Creek pipeline determined that a pre-existing hook crack was created in the original electric resistance weld when the pipe was manufactured. Prior to the explosion, the pipeline experienced a gradual increase in pressure as sour gas accumulates when the McMahon gas processing plant was temporarily shut down.

“The elevated pressure was sufficient to rupture the pipe along the longitudinal seam starting at the location of the pre-existing hook crack. The pre-existing hook crack had likely been growing over an undetermined period of time,” the report concludes.

Westcoast Energy Inc.’s pipeline integrity management program that was in effect at the time of the incident did not consider cracks and crack-like defects to be a significant potential hazard to the integrity of the Nig Creek pipeline, the report adds.

While the Guidance Notes for the Onshore Pipeline Regulations provide direction in developing a pipeline integrity management program, companies have the flexibility and discretion to develop the content of their pipeline integrity management program.

“It is the National Energy Board’s (NEB) expectation that regulated companies, as part of their pipeline integrity management program, proactively identify and continually monitor the specific hazards associated with their pipelines (regardless of vintage) and immediately update their pipeline integrity management program when new hazards are identified,” the TSB report states.

Following the accident, the NEB directed Westcoast Energy Inc. — a wholly-owned subsidiary of Spectra Energy — to conduct integrity assessments and repairs prior to seeking approval to return the pipeline into service.

Gary Weilinger, vice-president of strategic development and external affairs (Canada West) with Spectra Energy  Transmission in Calgary, says a number of safety measures around corrosion detection, pipeline integrity digs, pressure testing and visual inspections have been put into place.

He also cites changes in process improvements to detect metallurgical flaws like those found in the pipe that caused the explosion. “We do now x-ray all the wells and pipes that go into service for new construction,” Weilinger says. The energy company has also conducted a successful pressure test on the entire Nig Creek pipeline and filed a monitoring and verification plan for the pipeline’s fitness for service with the NEB.

It has also commissioned additional metallurgical analysis of other segments of the pipeline and scheduled an extensive inspection of the pipeline from the inside. A pipeline control room management review has begun and the resulting changes are expected to improve response times during an emergency.

“We do have a very, very thorough pipeline integrity management system in the place,” Weilinger says, noting that a number of issues have also been corrected to mitigate anomalies and the potential for future failures.

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