After an investigation into the rupture of the Exxon Mobil Pegasus pipeline that caused around 290,000 gallons of oil to leak into the small Arkansas town of Mayflower in March, the oil giant has issued a statement that cites a decades-old manufacturing defect as the cause of the environmental disaster. While this suggests that it was not corrosion from Tar Sands oil that caused the rupture, it does raise concerns as to the integrity of the pipeline, which runs from Illinois to Texas.

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The 850 mile-long Exxon Mobil Pegasus pipeline was laid way back in the 1940s, and in the intervening years Exxon appears to have been oblivious to the manufacturing defect that caused the spill. Exxon explained in a press release: “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.”

As John Upton at Grist explains “A seam is the welded part of a pipeline, either running along its spine or holding two pieces of piping together. By the American Petroleum Institute’s definition, a hook crack is caused by flaws at the edge of the metal plate used to create sections of pipeline.” In the case of the Pegasus pipeline, the tear that resulted from this flaw stretched 22 feet long.

How Exxon failed to notice—or ignore—such a vulnerability in the past 60 years is somewhat of a mystery. But the findings do raise concerns as to the potential for similar defects throughout the entire Pegasus system, and beyond. Upton continues: “The Pegasus system, which runs from Illinois to Texas, was laid in 1947 and 1948. The pipeline manufacturer, Ohio-based Youngstown Sheet and Tube Co., is no longer in business but was reportedly one of the leading suppliers of pipelines in the 1940s.”

In the meantime Exxon is continuing clean up efforts at the site, as the pipeline remains closed and Exxon faces Federal lawsuits under the Clean Water Act.

Via Grist