USS Nautilus hydrogen cracking during construction

The Nautilus was the first ship that had HY-80 in it, sometime in the '50s. They had all kinds of hydrogen cracking problems, such that some of the first subs they actually welded with austenitic stainless steel, because they couldn't solve the hydrogen cracking problem. It took them about 10 years to really get their arms around that, and then they had the Thresher problem and they had Subsafe. They didn't actually start putting HY-100 into ships until the late '80s. There were two ships before the Seawolf that they put modules — cylinders in the center of the ship — with HY-100. I'm familiar with that because my first student ever still works at Electric Boat as a welding engineer. He was in charge of welding up those HY-100 cylinders. When the Seawolf had all its cracking problems, the two captains who were in charge of the ships came to me and said, well, what about our two ships with the HY-100 that are out there? I said, don't worry about it, just inspect them when they come back in. They're not going to fall apart tomorrow — but they could fall apart if you didn't inspect them properly.

Centerpiece historical case of the lecture. Mid-1950s Nautilus mockup construction with HY-80; egg-crate stiffener welds made during the day; cracks audible as rifle-shot reports during the night shift — delayed hydrogen cracking, 8-hour diffusion timescale to crack tip. Workaround: switch to austenitic stainless steel electrodes (FCC structure, higher H solubility, lower cracking susceptibility) at the cost of undermatched strength.

But they did, when they went to build some of the mockup for the Nautilus submarine in the mid-1950s, which was the first nuclear sub. Before that they just used low-strength steel. The other night, Run Silent, Run Deep was on, and the Olympics hadn't come on, so I just put on this old Clark Gable, Burt Lancaster movie, and that submarine, when they dive deep, they go to 200 feet, because they just used regular old low-strength mild steel, whatever you want to call it, for submarines in World War II. For nuclear submarines, when they came with the Nautilus, they were using HY-80 — that's the piece I passed around — 80 ksi as opposed to 35 or 40 ksi. And so they could dive deeper. I won't tell you how much deeper, because it's classified, but it's a lot more than 200. It is more than double 200, because they did other things on the design and fracture mechanics and other stuff. They can go a lot deeper than 200 feet. But I can't tell you how deep.

Brief reference. Early Nautilus foundations welded with austenitic filler (half the strength of HY80) as a deliberate under-matching strategy to absorb hydrogen and limit residual stress, until higher-strength procedures were qualified.

The problem could be relieved if you could use an under-matching filler metal. If you could use a 7018 electrode, you can't build up residual stress greater than the strength of the weld metal — the weld metal is going to yield, and your maximal residual stresses won't be 110 KSI, they'd be 70 KSI, the strength of the under-matching filler. That's what they did in the early days of fabricating some of the foundations for the Nautilus. They had to go to an austenitic filler metal which had half the strength of the HY80 and would absorb a lot of the hydrogen. They were able to do it until they developed procedures that wouldn't crack with the hydrogen and the higher residual stresses they were encountering.