I seem to recall that when they were brazing the Sterling SMG tubes they encountered .013" or distortion, 'bananaring' the tube slightly. But later pushed up a water circulating filled copper cylinder that absorbed the excess heat. Another alternative was to stress into the tube a .013 distortion that would contract back to straight! On the other hand, Fazakerley just bent the tubes regardless and asked Sterling to straighten them!!!!! But mig or tig is the way to go, where the heat is both instantaneous and localised. And it's cooling immediately the tig is off.