none that I know of, maybe some others can elaborate.
when getting into material 1" and greater there's some consideration about minimum bead size to prevent shrinkage cracking. Although traditionally this is a problem with higher carbon steels, and can be overcome by preheating the material to 200-300 F.
The big thing for GTAW on thicker material is that the max feasible penetration and buildup in one pass is much more limited than other processes.
Mild steel is just about the most forgiving common metal, pretty hard to mess it up.
By Blaster 
Date 06-03-2010 04:14
Edited 06-03-2010 04:17
As base metal thickness goes up, the distortion can be horrendous because many welders won't keep up an adequate travel speed, and many welders won't deposit enough filler per pass which leads to a rediculous number of passes required to complete a joint.
