Fore River Bridge (Quincy)

Massachusetts drawbridge replacement, 8-inch-thick high-strength alloyed steel. Tom advised stopping every half-inch of weld for two hours to allow hydrogen diffusion. Used to illustrate that thickness-squared scaling makes hydrogen removal an engineering constraint, not just a metallurgical one.

There was the Fore River Bridge in Quincy — the state of Massachusetts is building a new drawbridge. They had eight inches thick of a high-strength alloyed steel, very difficult to weld. I told them, you've got to stop every half-inch for two hours to diffuse the hydrogen out. People had never heard of that — when you go to very thick steel you've got to stop to give time to the hydrogen to diffuse out, otherwise it's trapped forever. You start going through the diffusion equation, you're not going to get it out of there in any reasonable time. You'll get cracks before it all happens. So you have to worry about steel thickness as well.