I know this question has been addressed before, but I can't seem to find reason  why. Can anyone please help me understand why ASME limits a welder to the amount of weld he can deposit in a production piece and not base metal thickness qualified, whereas AWS only puts the limits on base metal thickness qualified. I can understand the reasons behind putting limits on WPS thickness, but not welder performance. Also, looking at ASME QW-452.1(b), it states that if coupon thickness is 1/2" and over with three layers minimum then the qualified weld metal thickness is "Maximum to be welded". What does that exactly mean? Sounds to me like as long as you use more than three layers your qualified to weld what ever thickness you need to in the field. Am I wrong?