The National Transportation Safety Board says a fatigue crack caused last year's rupture of the Keystone oil pipeline in South Dakota.
The NTSB said in a report released Thursday that the crack likely originated from mechanical damage to the pipe exterior caused by a metal-tracked vehicle during installation. Investigators say the crack grew to a "critical size" and resulted in the Nov. 16 rupture near Amherst.
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An estimated 210,000 gallons of oil spilled from the TransCanada Corp. pipeline between the Ludden, North Dakota, and Ferney, South Dakota, pump stations. There were no injuries associated with the incident.
TransCanada spokesman Matthew John says the impacted property has been cleaned up and the pipeline has returned to service. John says the company is committed to achieving its goal of "zero incidents."