Sea Wolf submarine hydrogen cracking / inspection case

1992 discovery by a grinder noticing sixteenth-of-an-inch swarf alignment from sub-eighth-inch cracks the inspection equipment couldn't reliably find. $2B repair, 18% of hull complete at discovery. Tom was one of two individual advisors to Admiral Firebaugh, then-Chief Engineer of the Navy. Used to teach: critical flaw size in the steel is several inches; the sixteenth-inch cracks are below the detection threshold; you don't have to derate the submarines, you just inspect for growth at scheduled maintenance.

To give you a specific example: in 1992 the US Navy was building a two-billion-dollar submarine down in Groton, Connecticut, called the Sea Wolf — the 21st-century submarine. It had been designed by Captain Millard Firebaugh, an MIT grad who got his PhD in what's now Course 13, then Ocean Engineering. He was in charge of designing the Sea Wolf in the 1980s, when I first met him. They built it in 1992. A guy was grinding the outside surface of the hull. The hull has to be about 30 feet in diameter, plus or minus a quarter of an inch, smooth. Little ripples of a quarter of an inch — like weld reinforcement — create sonar noise, and they'll find you. So a guy was grinding this and he noticed, as he was grinding, the swarf — anybody know what swarf is? If you like Scrabble, that's not a bad Scrabble word. Swarf is the particles that come off in grinding. He saw the swarf was lining up in sixteenth-of-an-inch lines. The welds were full of little sixteenth-inch cracks, and they hadn't found them. They had done their inspections, but their equipment is designed to find an eighth of an inch and larger, because that's what the standard says, because that's what you can reliably find. He noticed it, said, I've never seen that before, told somebody, and they found the entire submarine — eighteen percent of the hull was completed — full of these little cracks.