SSN-21 Sea Wolf hull cracking problem

Even with prototype experience, Sea Wolf hull welding had major problems. In §7 the case is developed: they thought they had HY100 filler but got HY80-equivalent due to property scatter, hydrogen control inadequate, 18% of the ship welded with undermatched filler.

This is another problem with our pressure vessels. You guys still use ASME pressure vessel steels. Almost all of those were developed in the 1940s, and it would cost probably half a billion dollars to qualify new steels for pressure vessels. The Department of Energy has tried to qualify 9% nickel steel — sorry, nickel-1-molybdenum — to use at higher temperatures for some of the nuclear reactors. They've been doing this for 40 years, and people are still somewhat hesitant. They haven't got a big enough database out there until you actually start building prototypes and get experience. That's why the Navy, before they went to an all-HY100 hull, built a couple of full-size 30-foot-diameter sections for a couple of boomers back in the 90s and put them in service, even though they were still on HY80. They wanted to get the experience with welding it. And even when they did go to a full-sized ship — Sea Wolf in the 90s — they still had major problems. One of the reasons for building things like Alvin and the Sea Cliff was as part of the prototyping research exercise. You build small submersibles, deep-submergence things, but it also gives you experience with fabricating what they hoped would be the next HY-series alloys.

A grinder smoothing welds on the first Seawolf-class submarine noticed grinding swarf lining up in lines under a sixteenth of an inch — a flaw size below anything the specification had ever required inspectors to find. Destructive sampling revealed clusters of micro-cracks throughout the welds; 18% of the hull had been completed. Tom contributed to the investigation report and identifies the weld-wire chemistry being on the high side as a contributing factor. Repair costs Tom heard ranged from half a billion to ~$2 billion — comparable to building a new boat. Two Seawolves were built before the program was canceled with the end of the Cold War. Tom uses the case to dramatize how improvements in measurement capability create disputes about flaws the original specification never contemplated.

So what happened to the Seawolf submarine? They were looking for eighth-inch flaws. That's what the codes say. That's what reality says is all you can find with any probability. But what happened is some grinder was grinding the weld smooth. On a submarine you can't have these big humps of a weld when you're going through the water — it's amazing how quiet these things have to be. They have to grind the weld flat. This grinder grinding the weld notices that the swarf — the little particles from grinding, called swarf, good Scrabble word, S-W-A-R-F — the swarf is lining up in little lines, less than a sixteenth of an inch in length. He says, I've never seen that before. He goes and tells someone, and someone says, hm, I've never seen that before. They start investigating it, and the welds had a whole family, a cluster — they were full of these little micro-cracks.

Brief reference. Source of lessons on welding high-strength steels. Used as a parallel to the Thresher in Petroski's framing of "we learn from failure."

Henry Petroski, a guy at Duke University in the civil engineering department, wrote a book called To Engineer is Human. He's gotten famous off it, elected a member of the National Academy of Engineering. The book is about how we learn to engineer new structures from failures. We learn from the Sea Wolf problem — expensive lesson to learn, but we learned a lot about welding high-strength steels we didn't know about. We learn about process control from the Thresher — the whole SUBSAFE program came out of the Thresher disaster.