Get someone to furnish you some 10 or 12 inch pipe. It is a world of difference welding 4 inch and 12 inch. Throw away 1/8 welding rods for the bead. If you cant run a 5/32 bead, most pipeline outfits will not mess with you. Unless they are running a bunch of 3 and 4 inch gathering lines. But to pass the test you will need to be able to run the 5's and 3's. 5/32 and 3/16. Also get to a good welding supply house and get a copy of Graves Blue Book. A lot of inspectors require laying out the branch using a Blue Book and adding machine tape. If you can help a welder for a few months to get the pace of pipelining down, it will not be such a strange world. Then ever chance you get, run some nipples. Do a couple of branches. The branch test is not so much a welding test as an endurance test. I seldom see experienced welders not try to help out some breaking out. There are a few, but shine them on. Pipelining is a different world than shop work and the bets way to learn would be to hire on for a job as a helper and just see what the game is. Talk to the welding boss. Tell him what you want to do. Tell him you can weld but need experience. If you can make him a hand, they will let you carry off all the pipe you want. As an inspector I always will give drops to helpers who say they want practice nipples. It just goes for scrap anyway.
Good Luck and I hope to get the chance to test you one day, shake your hand, and give you a stencil.