Neutrons Map Hidden Stress in Submarine Hull Welds

Summary

• ORNL is using neutron methods to study weld-joint integrity in U.S. Navy submarine pressure hulls.
• The target issue is ductility dip cracking (DDC), which can form during weld cooling and weaken joints over time.
• Work includes 70/30 copper-nickel welds, with residual stress mapping on the HIDRA instrument at HFIR.

U.S. Navy nuclear submarines can operate more than 800 feet deep, where hull welds must survive extreme water pressure, so long-term weld integrity is a safety-critical topic. Researchers at Oak Ridge National Laboratory (ORNL) are running neutron experiments to better understand how welded joints behave over time in these pressure-hull structures.

The key weld problem in focus is ductility dip cracking (DDC): small cracks that can form as welded metal cools and solidifies, then slowly grow and weaken the joint. The team is studying DDC in a widely used naval alloy—70% copper / 30% nickel—through a collaboration involving the Navy, Electric Boat, and the University of Connecticut.

A big tool here is neutron scattering at HIDRA (High Intensity Diffractometer for Residual Stress Analysis) at ORNL’s High Flux Isotope Reactor. Neutrons can penetrate thick metals and help map residual stress without cutting up the sample, and the researchers say HFIR’s neutron output allows faster measurements (hours, not weeks). They also note the neutron results complement X-ray testing at Brookhaven.

Source:

Neutrons dive deep to help protect US nuclear submarines

America’s national security relies in part on the U.S. Navy’s nuclear-powered submarines, which can operate more than 800 feet 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 pounds per square foot.

Tech XplorePaul L Boisvert