Manufacturing improvements between the 1940s and 1970s brought "better quality control, higher strength and improved weldability," he added.

Richard Kuprewicz, pipeline safety expert and president of Accufacts Inc., Redmond, Wash., does not call for replacement of the older pipe, saying it would not all be subject to the seam risk.

But, Kuprewicz also said, "They apparently have a batch or more than one piece [at risk]. It could be a system issue or a partial system issue."

Such a flaw is hard to detect in an online inspection, he added.

Meanwhile, the U.S. Environmental Protection Agency, the state of Arkansas and individuals who own property on nearby Lake Conway have filed federal lawsuits against ExxonMobil.