Exxon: Defects in pipe caused Arkansas pipeline rupture
BY ALISON SIDER
IRVING -- An independent report found that a rupture in an ExxonMobil pipeline that spilled thousands of barrels of oil in Mayflower, Arkansas, earlier this year was caused by defects dating back to when the pipe was built in the 1940s, the company said.
An independent metallurgical laboratory looked at the section of the pipe that ripped open in March, spilling an estimated 5,000 bbl of oil into a residential neighborhood in the small town about 25 miles from Little Rock.
Exxon said Thursday it is reviewing the results of that assessment, which were provided to the company and the Pipeline and Hazardous Materials Safety Administration on Wednesday.
The Texas oil giant said that according to the report, hook-shaped cracks along the pipe's seams were the root cause of the pipe's failure, not corrosion. The cracks are related to an outdated welding process that is no longer performed on new pipes, but that still affects thousands of miles of pipelines in use across the U.S.
The lab also found that the pipeline's limited flexibility also contributed to the incident, Exxon said. The report has not been made public, and PHMSA is still reviewing it, a spokesman for the agency said.
The section of the pipe that ruptured is more than 60 years old, but passed a high-pressure test in 2006 and an internal inspection in 2010 that sought to measure metal loss or other anomalies, Exxon said.
Aaron Stryk, a spokesman for Exxon, said the full results of a more detailed inspection Exxon conducted earlier this year are not yet available. That inspection, called a transverse flux, uses a magnetic field to find corrosion along seams. It can also detect cracks and other defects, though not as reliably as it can detect corrosion, according to PHMSA's website.
Once the results come out, the company will review whether it needs to make changes to its pipeline integrity management program, Mr. Stryk said.
But it is not clear how reliable that test will be in detecting potential problems along pipeline seams, said Rick Kuprewicz, a pipeline safety consultant.
"That's the million dollar question," Mr. Kuprewicz said.
The type of cracks found to have caused the rupture in Mayflower are associated with some types of an early welding process called electric resistance welding, according to PHMSA's website. That process hasn't been used on new pipelines since about 1970, but about a quarter of the 182,500 miles of liquid fuel pipelines across the U.S. were welded that way, according to the most recent federal data.
Other pipeline ruptures have been linked to electrically welded pipe over the years, including a 2007 break in a liquid propane pipe near Carmichael Miss., which caused a fire that killed two people. In 2011, PHMSA commissioned a study of how to detect problems in these pipes and prevent them from failing while in use.
Arkansas and the U.S. government have sued Exxon for allegedly violating pollution laws. The Arkansas attorney general has not yet seen the testing results, a spokesman for the office said.