John Wolfe stainless steel sensitization patent (1940s)

Wulff's 1940s patent: deliberately sensitize stainless steel, immerse in nitric acid overnight, dissolve chromium-depleted grain boundaries to produce stainless steel powder. Used pedagogically to show that the same intergranular attack mechanism that makes BWR welds fail is exploited industrially for powder production.

In fact, John Wulff, my academic grandfather, had a patent in the 1940s to sensitize stainless steel, heat it in this region, get something like this, throw it in nitric acid overnight to make stainless steel powder. The nitric acid doesn't attack the 18% chrome, it does attack the 10% chrome, eats away the grain boundaries, and you get typical intergranular cracking. This cost General Electric a couple billion dollars in the nuclear reactor industry in the '70s from the welds getting sensitization cracking. If you were Westinghouse, you used Inconel — about ten times the price of stainless. If you're building a pressurized water reactor, because of the higher temperatures, they needed Inconel. General Electric had a boiling water reactor, they could use stainless — less expensive material but more susceptible to stress corrosion cracking. You get cracks through the reactor safe end. That means that you're not going to be able to flood the reactor with water if you have a near meltdown. And you will not have a near meltdown — you'll have a real meltdown.