Keystone spill caused by crack that progressed over time: TC Energy

TC Energy Corp. says a third-party investigation into an oil spill from the company's Keystone pipeline in December has concluded the incident was caused by a crack in a weld that occurred at the time of the pipeline's construction.

The Calgary-based company says the affected pipe segment was subjected during construction to "inadvertent bending stresses," initiating a small crack that progressed over time to pipe failure after a decade of operations.

TC Energy says the findings are consistent with the conclusions from an earlier metallurgical analysis, the results of which the company released in February.

The Canadian company is still on site cleaning up the mess. It says it has recovered 98 per cent of the spilled oil and remediated 90 per cent of the creek's shoreline.

Last month, the U.S. Pipeline and Hazardous Materials Administration expressed concern over the risk of additional spills from Keystone, and ordered TC Energy to operate the pipeline at a reduced pressure until it receives written permission from the regulator.