Exxon points to rare chemical mix as Pegasus flaw | Arkansas Blog

Tuesday, April 1, 2014

Exxon points to rare chemical mix as Pegasus flaw

Posted By on Tue, Apr 1, 2014 at 5:03 PM

Exxon issued a  Monday of the remedial work plan it submitted to the federal agency that regulates pipeline over the weekend on the Pegasus pipeline, which expands upon its earlier finding that a manufacturing defect in the low-frequency electric resistance weld pipe (ERW) caused the joint crack that sent 210,000 gallons of crude oil spewing into a Mayflower neighborhood last year. Exxon's summary now says that "atypical pipe properties [are] the most significant contributing factor" to the break." Company vice president Karen Tyrone, vice president of Exxon Mobil Pipeline Co.,  also referred to the joint's "extreme metallurgical properties" in an interview with Talk Business.

By putting the focus on the atypical properties — a chemical stew of sulfur, manganese and carbon company officials say they've never seen to such an extent in a joint before — and away from a well-known manufacturing defect of the ERW pipe used in the northern section that includes Arkansas, it would seem that Exxon is casting the rupture as caused by a rare flaw.

Does Exxon believe that the atypical chemical properties in the 648-mile pipeline only occur in Mayflower? 
Richard Kuprewicz of Accufacts Inc., a pipeline safety consultant working with Central Arkansas Water, which would like to see Exxon move the pipe away from Little Rock's drinking water supply, said that ERW pipe can have "some strange chemistry" that might contribute to pipe failure; the industry is used to seeing strange chemistry in certain batches of pipe. He acknowledged that he has not seen the chemical makeup in the section of pipe that Exxon has seen, and that it could indeed be higher than elsewhere.

Exxon also announced it would conduct a spike hydrostatic test along the line, which involves shooting water through the pipe above its maximum operating pressure to test for weaknesses. If the pipe fails in a few places, pipe can be replaced. If it fails all along the line, one would think the pipe should be abandoned.

The Exxon summary said the test would be performed at a higher-than-maximum operating pressure to detect leaks. "The devil is in the details" on how the test is performed, Kuprewicz said. "What is your pressure range? That is the real key."

Exxon conducted hydrostatic testing along the pipeline in 2005 and 2006. Yet the Pegasus failed at below the maximum operating pressure. "Something happened to cause the imperfection" in the ensuing years, Kuprewicz said, though because he is an impartial party, he declined to speculate what. "The important thing is that [Exxon is] heading in a positive direction." 

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