USS Sea Wolf submarine hull cracking

Around 1992 at Groton (Electric Boat), the Navy moved from HY-80 to HY-100 for the Sea Wolf hull. A grinder noticed swarf lining up along sub-eighth-inch cracks in completed welds. Re-inspection found all welds (18% of hull complete) full of microscopic hydrogen cracks. Required scrapping the completed portion, delaying the program a year and costing ~$2 billion. Fix: preheat the steel to 400°F, with welders working in recirculated-liquid blue jelly suits inside heated submarine compartments.

Hydrogen embrittlement occurs all the time. The US Navy down in Groton was going to a higher-strength submarine steel, from HY-80 to HY-100. Didn't seem like a big change. They had promised Congress in the early nineties that they would eventually start making the 21st-century submarine out of HY-130, which they developed in the 1960s, but they never had the nerve to actually build a whole ship out of. So they're starting to build a whole ship out of HY-100 — this is the Sea Wolf, the first edition of the 21st-century submarine, around 1992. Higher strength by 20 ksi, going from 80 to 100 ksi yield strength. The inspectors look for flaws an eighth of an inch in size or larger, and they found none in the welds. Some guy's grinding the surface of the hull to make a smooth contour — you can't even have a little weld reinforcement, because going through the water it creates enough noise that they can pick it up on sonar. So they have to grind it smooth. This grinder noticed that the grinding swarf, the little iron oxide particles, was lining up in these little less-than-eighth-of-an-inch-long parts in the weld metal. He was smart enough to tell someone, and they came in and did more thorough non-destructive testing — and all the welds, 18 percent of the hull had been completed, all the welds were full of little microscopic cracks they had never seen before.