When butt welding 12 ga. carbon steel plate with the short arc process, .035 70S6 wire,and C25 gas, will depositing the weld bead on the second side of the joint, penetrating the weld of the fist side cause an under bead crack?
12 ga, carbon steel (0.10 in.) can be welded best full penetration from one side with the process you describe.. First question would be why not do it that way?
How did you identify the under bead crack?
If there was joint restraint maybe, but it might also be oxides present if the back side was not cleaned/routed thoroughly that left some sort of discontinuity to be found by.... RT? UT? Section and etch?