As we are working on quite a few TYK joints right now, it is true that .045 FCAW-G can be done open root CJP without a problem. However, AWS does not limit the melt-though on the back side of the joint. If this was limited, as is normally the case with butt joints that are fluid containing (instead of structural as is the case with TYK), I think it could be another matter to get consistancy. In out limited experiments, we could only get consistant melt-though on the back side of butt joints with rotated pipes in the horizontal position. I'm not saying it can't be done, it just seems harder than most of the FCAW welders are capable of doing consistantly.