photo by: Kyle Bauer/KCLY/KFRM Radio via AP

A remediation company deploys a boom on the surface of an oil spill after a Keystone pipeline ruptured at Mill Creek in Washington County, Kansas, on Thursday, Dec. 8, 2022.

Canadian oil company TC Energy said Thursday that faulty welding contributed to an “instantaneous rupture” in its Keystone pipeline that gushed hundreds of thousands of gallons of extra sticky tar sands crude oil onto Kansas native prairie, cropland and into a creek.

The federal government required the company to have a third party conduct metallurgy tests. The Kansas News Service has filed an open records request for the full results.

TC Energy also gets three months to complete an analysis of the cause of the spill. That report must be “supplemented or facilitated by” a third party. The analysis isn’t finished, but TC Energy said in an online post early Thursday that the mechanical and metallurgy results had come back.

It says those tests point to factors including “bending stress on the pipe and a weld flaw.”

TC Energy seemed to point a finger outside its own ranks, saying the weld flaw was made at a “fabrication facility.”

“The weld flaw led to a crack that propagated over time as a result of bending stress fatigue, eventually leading to an instantaneous rupture,” TC Energy wrote in its press release. “The cause of the bending stress remains under investigation.”

The company said welding inspection and testing had complied with “applicable codes and standards.”

It also said the pipe itself showed no defects.

And it said the Keystone was operating at a legal pressure level when it burst.

The Kansas News Service submitted an open records request in December for a report that shows the precise pressure levels at the time of the rupture.

In late December, the federal government allowed TC Energy to restart the pipeline, on the condition that it operate for the time being at a lower pressure than when the rupture occurred.

“Our focus continues to be the safe operation of the pipeline system,” TC Energy wrote in its press release.

The federal government is also requiring TC Energy to look for other potential weak points within the 96-mile stretch of the Keystone system that includes the site of the spill in Washington County near the Nebraska border.

That stretch runs from Jefferson County in Nebraska through Washington, Clay and Dickinson counties in Kansas.

• Celia Llopis-Jepsen reports for the Kansas News Service.