Pre-existing defect caused January 2014 pipeline rupture in Manitoba, transportation safety board says

A pre-existing defect led to a January 2014 pipeline rupture in Otterburne, Manitoba, the Transportation Safety Board of Canada (TSB) said in its investigation report into the incident, released on Tuesday.

On Jan. 25, 2014, Line 400-1, a 30-inch natural gas pipeline operated by TransCanada PipeLines Limited ruptured and ignited at the site of Mainline Valve 402 near Otterburne, ejecting debris about 100 metres from the rupture site, the TSB said in a statement. The escaping gas burned for approximately 12 hours and five residences in the immediate vicinity were evacuated until the fire was extinguished.

The TSB investigation determined that Line 400-1 failed due to a fracture that occurred at a “pre-existing crack that had remained stable for over 50 years prior to the occurrence,” the safety board reported. “This crack had formed at the time of the pipeline’s construction, likely due to an inadequate welding procedure and poor welding quality,” the TSB said, adding that there was no requirement for inspections of every weld by radiography at the time of the pipeline’s original construction.

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The fracture was caused by incremental stresses to the pipeline, which were likely due to a combination of factors, including: weakened soil support in the area due to maintenance activities over the years; record low temperatures that winter; recent work at and around the valve site that may have driven frost deeper into the ground; and thermal contraction that may have occurred when the pipeline cooled due to the absence of gas flow for 20 days prior to the incident.

Following the occurrence, the National Energy Board required TransCanada to perform several engineering assessments along Line 400-1. TransCanada performed numerous excavations, inspections and repairs along Line 400-1 before returning it to service. Following the pipeline’s return to service, TransCanada performed in-line inspections to rule out other threats to the pipeline’s integrity, the TSB added in the statement.