(Oak Ridge National Laboratory: Oak Ridge, TN) -- America’s national security relies in part on the U.S. Navy’s nuclear-powered submarines, which can operate more than 800 ft below the ocean’s surface. At such dark, unforgiving depths, the crew’s survival depends on the ability of the sub’s steel hull—and its welded joints—to withstand immense water pressures that can exceed 50,000 lb/sq ft.

As much as 200 yards in length, the submarines’ pressure hulls consist of many steel plates measuring up to 100 ft long, all joined by precision manual or robotic welding methods. The long-term integrity of the welded joints, or seams, where the plates meet are the subject of neutron experiments at the U.S. Department of Energy’s Oak Ridge National Laboratory.

Despite meticulous quality control during welding on submarines, the problem of ductility dip cracking (DDC) has not been completely eliminated. It can occur when welded metals cool and solidify, causing small cracks to form and propagate around a weld, which weakens the joint over time—even with the latest steel alloys.

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