Well, no.. I wouldn't bugger weld them on if I didn't know what I was doing, but a competent welder should have zero issues making strong, good, pretty welds on a frame. I would venture to say that the area affected by the welder would be no weaker then the areas with holes in them for bolts all over the frame. While it won't make it stronger, a good welder will not overheat the area and it should be more or less the same strength as it was prewelding. It's not anything fancy, it's mile steel being welded to mild steel.