I used to make stock racks (2" sq tube, .120 wall) for a corrugated company for about 5 years. Forklifts typically destroyed the racks, but we never had a tube tear the weld apart - it would always tear out the whole tube itself - the weld was stronger than the .120 wall mild steel. Again, they were welded horizontally, vertically, and across the bottom. I don't buy that a MIG weld is for top surfaces only.

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Thats called the "heat affected zone" thats the reason
that moly tubing is tigged to keep the heat down...
it will always tear in the "HAZ" unless its a junk
weld and it breaks the weld