NEW YORK Manufacturing defects around the weld seam of an Exxon Mobil Corp. oil pipeline in Arkansas caused its failure in late March, according to a metallurgical report.
"Based on the metallurgical analysis, the independent laboratory concluded that the root cause of the failure can be attributed to original manufacturing defects, namely hook cracks near the seam," Exxon said in an e-mailed statement.
"Additional contributing factors include atypical pipe properties, such as extremely low impact toughness and elongation properties across the electric-resistance weld (ERW) seam," the Irving, Texas-based company added.
Internal or external corrosion did not play a role in the failure, according to the analysis by Euless, Texas-based Hurst Metallurgical Research Laboratory Inc.
Exxon is conducting supplemental testing to "help (it) understand all factors associated with the pipe failure" and "ensure a similar incident does not occur again," it said.
In the meantime, the affected Pegasus oil pipeline remains shut "until we are convinced it can be safely restarted," a company spokesman said in an e-mail.
The Pipeline and Hazardous Materials Safety Administration did not return a request for comment, while an Exxon spokesman declined to name the pipe supplier.
The 850-mile line, which carries Canadian heavy crude oil to the Texas Gulf Coast from Patoka, Ill., ruptured near the city of Mayflower, Ark., on March 29, spilling about 5,000 barrels of oil and leading to a sustained cleanup effort by Exxon (amm.com, April 2).
The incident was categorized as a "major spill" by the Environmental Protection Agency. The state of Arkansas and the U.S. government have since filed a joint complaint in federal district court in Little Rock, Ark., seeking civil penalties against Exxon, according to a statement by the Department of Justice.
The Pegasus line, which was built in the 1940s, consists of 20-inch-diameter X42 seamless and low-frequency ERW pipe of 0.312-inch wall thickness (amm.com, April 3).