A simple mean doesn't fully illustrate what's going on there. Most welders are self-taught, and while their skills are more than adequate for what they're doing they likely don't have the skills necessary to (for instance) weld stainless steel or aluminum.

A welder who graduated from Tulsa Welding School with a year or so of training is likely going to start out somewhere around $50k. I have a friend who went there and specialized in underwater welding, and now he works for BP in the Gulf somewhere. His job consists of mostly inspecting the work of his juniors, and he makes about three times what I make as a software engineer.