Andrew R Stewart 

Wow, lots of stuff flying out in the wind of this thread.

There is no bad material, only bad design. Bubble gum could fix this crack, if enough could be crammed in to the space. The millions of bikes with brass brazing prove that this joining method is good enough if done properly. One of the reasons that brazing is so popular is that the fudge factor is larger then welding. That the frame was welded and there is a crack might suggest as much. Welding requires that the tubes get hot enough to melt and then cool down. This much heat has many effects on the steel (and other tube materials), as mentioned. If not done well the changed steel's metalurgical qualities might not be up to the task. Add a stress not designed for (too little post insertion) and no wonder the tube cracked near the weld.

As for the motorcycle comparison bike tubing (531 and 4130) has been used before. Not in bike diameters and gauges but with brazing. The problem with lump claims of failures is that one rarely gets the chance to examine the failed joint. How well was the joint designed, preped (mitered, cleaned), how much flow of filler, how much fillet, any finishing undercutting. Of course the higher stresses and vibrations of motorcycling makes the need for proper joints greater.

I still say that a patch of suffecient size, brazed over the drilled at each end crack, is the most likely repair that will have fewest after effects.