Rocky Flats nuclear warhead welding - altitude pressure effects

Process developed at Oak Ridge (low elevation), transferred to Rocky Flats outside Denver (5,000 ft, ~0.82 atm). Weld pool geometry changed enough that DOE put the whole operation in a pressurized chamber — "PIGMA welding," documented in Welding Journal papers in the early 1980s without explanation of motive.

Well, welding has altitude sickness too. Denver is the Mile High City, and they developed a process to make nuclear warheads at Oak Ridge in Tennessee, which is less than a thousand feet — probably five or six hundred feet elevation. After the development process, they took it to Rocky Flats in Denver, which is now the Denver airport. They wanted to put it into production. It turns out the atmospheric pressure there is about 0.82 atmospheres. So it didn't work the same — the shape of the weld pools wasn't the same when you lost 20 percent of your pressure. They actually had to put the whole thing in a pressure vessel and pressurize it. They called it PIGMA welding. If you look in the literature back in the early '80s you'll see papers in the Welding Journal: pressurized inert gas metal arc welding, or something like that. They didn't exactly explain why they were doing it. But the scuttlebutt is that the Department of Energy developed it at Oak Ridge and moved it up to 5,000 feet, and the arc characteristics changed enough — pressure does affect arcs. But you have much higher pressures in underwater welding.

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