Tuesday, April 16, 2013

Old Oil Pipeline Welds Vulnerable To Failure

Exxon Mobil pipeline spill in Mayflower, Ark.
Recent pipeline ruptures are raising fresh questions about the safety of pipes made decades ago using obsolete welding techniques.  The accidents come as federal regulators are examining whether state-of-the-art inspection methods are capable of detecting flaws in these old pipe seams.  Though the industry stopped making what is known as low-frequency, electric-resistance welded pipe by about 1970, it still accounts for more than a quarter of the 182,500 miles of liquid fuel pipelines across the U.S., according to federal data for 2011, the latest available.

An Exxon Mobil Corp. pipeline rupture caused a major oil spill last month spilled about 5,000 barrels of oil that ran through a Mayflower, Ark., development after a 22-foot split opened.

A Chevron Corp. pipeline in Utah last month that spilled 600 barrels of diesel near the Great Salt Lake, segments of the pipes were made about 60 years ago by bending metal sheets to form a tube, then heating the edges with a low-frequency electric current to weld them lengthwise. Such welds can leave defects in seams that make them vulnerable to corrosion and cracks, risks that have been known for decades. By 1970, most pipe manufacturers began using a high-frequency current to weld, which produced seams less prone to fractures.
The Chevron pipeline appeared to split along the welded seam, according to federal regulators. A Chevron spokesman said while the investigation continues, "Initial indications are that the release may have been the result of a longitudinal seam failure in the pipeline."
The Exxon pipeline gushed about 5,000 barrels of crude into a residential neighborhood through a 22-foot, incision-like break.

Of the 1,151 accidents on liquids pipelines since 2010 reported to federal regulators, 78% don't show what kind of weld was involved, and 85% don't show when the pipe was manufactured, according to a Wall Street Journal review of government data. The Pipeline and Hazardous Materials Safety Administration (PHMSA) says most of the accidents involved very small spills, or weren't related to pipe welds, so operators weren't required to furnish detailed information about them.

But the number of pipeline accidents has been rising; the 364 accidents on liquids pipelines last year were the most since 2008, but fewer than in 2002, according to federal data.

Clean-up crew removing crude oil from a Mayflower, Ark., Associated Press
Federal regulators are questioning the adequacy of inspection methods. The surest way to identify a weld defect is to pump water through the pipe at high pressure. Such tests are costly, requiring a company to shut down the line, and in some cases apparently led to failures when placed back in service.
The other chief testing method involves running a robotic device through the interior of the pipe to detect any anomalies. This device, commonly called a "smart pig," has at times failed to catch flaws that later resulted in a rupture.  Neither test is foolproof. (WSJ, 4/15/2013)

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