The National Transportation Safety Board identified a fatigue crack to be the probable cause of the Nov. 16, 2017, rupture in TransCanada Corp.'s Keystone pipeline which led to an oil spill south of the Ludden pump station in Marshall County, S.D.
The fatigue crack likely came from mechanical damage to the pipe's exterior during its installation, caused by a metal-tracked vehicle, which grew to a critical size, the agency said in a July 5 report following a limited investigation which focused on a metallurgical investigation of the ruptured pipe.
TransCanada shut down the pipeline in response to the rupture, which then leaked an estimated 407,400 gallons, or roughly 9,700 barrels. The U.S. Pipeline and Hazardous Materials Safety Administration on Nov. 28, 2017, suspected that the rupture was caused by construction damage that occurred during the pipe's installation.
PHMSA on May 1 cleared TransCanada to restore pressure on Keystone, but required the company to lower the pressure on the affected segment by 20%, pending corrective actions.