WINNIPEG—The Transportation Safety Board of Canada has released its investigation report into the Jan. 2014 rupture of a TransCanada PipeLines, natural gas pipeline.
The board said on Jan. 25, a 30-inch natural gas pipeline, Line 400-1, ruptured and ignited at the site of Mainline Valve 402 near Otterburne, Manitoba. The escaping gas burned for approximately 12 hours.
The 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. This crack had formed at the time of the pipeline’s construction likely due to an inadequate welding procedure and poor welding quality, TSB said. The board also noted there was no requirement for inspections of every weld by radiography at the time of the pipeline’s original construction.
The report found the fracture was caused by incremental stresses to the pipeline, which were likely due to a combination of factors. These included: 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 occurrence.
Following the occurrence, the National Energy Board required TransCanada to perform several engineering assessments along Line 400-1, and the company performed numerous excavations, inspections and repairs along Line 400-1 before returning it to service. Following the pipeline’s return to service, TransCanada also performed in-line inspections to rule out other threats to the pipeline’s integrity, TSB said.