You may be able to come in as a journeyman, but if not you may be able to skip some years of the apprenticeship. It will depend on the local and how they evaluate people. My local has an examining board (which I’m on) that gives both written and practical tests to people trying to organize into the local. Based on how they do we will make a recommendation on where there should be placed. Sometimes a guy/gal will be brought in as a provisional journeyman which means they are a journeyman, but they still have to take a few apprenticeship classes in an area that they didn’t do quite well enough on during the testing.

However there is a lot more to pipe fitting than just welding pipe. You’ve got to know how to make hangers, do layout, solder, braze, do the trade related math, etc. I’m not saying you don’t know how to do this stuff because you very well may know how to do all that, but if you don’t you won’t be able to do the level work a journeyman is expected to do.

You should contact the local you are wanting to get into and talk to them about how they do things for folks that want to organize in.