Well, failure is always an option....

But I don't think you're familiar with the type of fitting I'm thinking of. Once you get up to the size required to be a decent fit for average frame tubing size you'll have some really chunky pieces of metal, with plenty of cross section area in all the parts. Sudden failure of that joint isn't worrying me at all.

Compared to all the rusty, crashed, cracked and otherwise compromised frames/forks I've ridden over the years, often unknowingly, I'd happily trust my safety to a recently installed and inspected 1" or bigger union coupling w/o any concerns.





I'd machine out the threads intended to go on the pipe ends, insert the frame tubing there and braze the fitting on to the frame tube.

They're available in steel too, if chunky brass for some reason wouldn't feel "safe" enough.
What I might wonder about though, is if the frame would stay in alignment well enough to be properly rideable, and if the added thickness of the fitting would somehow get in the way of the regular use of the bike.