Stress put on the Keystone pipeline during construction, its operator said Friday, contributed significantly to it bursting in north-central Kansas.
TC Energy says an independent review shows the sequence of factors that led to the Keystone’s rupture in December that fouled a creek and spewed oil over cropland and prairie.
The ill-fated segment experienced “inadvertent bending stresses sufficient to initiate a crack” during its construction in 2011, the company said in a press release about the findings.
The Washington County spill was the biggest in the Keystone’s history, and the second-biggest spill on U.S. soil of dilbit, a Canadian tar sands product that presents particular environmental risks and cleanup challenges when it spills into bodies of water.
The company didn’t release the document, but outlined its version of “the key findings” in it.
Federal officials ordered TC Energy to commission the pipeline failure analysis. The government told the Canadian company to hire an independent contractor to help with the analysis and to “document the decision-making process and all factors contributing to the failure.”
The federal agency — the U.S. Department of Transportation’s Pipeline and Hazardous Materials Safety Administration — also received the report on Friday, but it hasn’t commented publicly yet on the conclusions.
TC Energy says the report found that “a progressive fatigue crack” was the main cause of the oil spill.
The crack started at a welded spot in the pipeline that connected an elbow fitting to the pipe segment across a creek.
“Bending stresses during construction also led to a deformation in the elbow fitting and a wrinkle in the adjacent piping,” the company said. “Further, the design of the weld transition created a stress concentration point, making the pipe at this location more susceptible to bending stresses.”
The company says the fitting and pipe “met all strength and material property design and code requirements.”
It also says the Kansas section of the Keystone never operated above the stress level normally permitted for such pipelines, even though it had received special federal permission to exceed those limits.
The federal government had also ordered TC Energy to investigate whether similar conditions elsewhere along the Keystone could lead to the same tragic consequences.
TC Energy said Friday that it is “in the process of implementing a comprehensive plan … to enhance our pipeline integrity program and overall safety performance.”
It said it is carrying out extra inspections and examining “other sites with characteristics like the incident location sites.”
