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.
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
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).