The two-year anniversary of ExxonMobil's oil pipeline rupture in Arkansas is once again putting the spotlight on old pipe that can harbor cracks and other dangerous defects—and that's still in widespread use across the country.
Federal regulators have known for decades that vintage pipe carried extra risks. After a spate of new spills, however, they recently took the first step toward mandating more rigorous testing on pre-1970 pipe, including the kind that was a factor in causing ExxonMobil's oil spill in Mayflower, Ark.
The failed section of ExxonMobil's Pegasus line was manufactured in the 1940s using low-frequency electric resistance welding (LF-ERW), a process that was widely used from the 1930s into the 1960s. The technique was phased out by 1970 because it left flaws in the steel that could cause pipelines to split open along the lengthwise seams.
Nationwide, there are about 48,400 miles of that kind of pipe in use, equal to 25 percent of the total miles of pipelines carrying oil, gasoline and other hazardous liquids. The inferior pipe is woven into the natural gas pipeline network as well, but the amount is not known because gas pipeline companies aren't required to quantify their LF-ERW pipe.
Not all LF-ERW pipe has defects like the hook-shaped crack that set the stage for Exxon's pipeline to break open. But regulators consider all of it at-risk because many pipeline companies inspect their lines using sensor-laden robots, and those devices can't reliably find microscopic cracks that could be lurking in LF-ERW pipe.
Here are the five companies with the most LF-ERW pipe carrying oil and other hazardous liquids, according to 2013 data from the Pipeline and Hazardous Materials Safety Administration.