I had the misfortune of using a Big 20 on a company rig for about nine years. They have a very weak arc and in order to get the bead in you had to run hotter to keep it from sticking. The increase amps caused internal under cut in most cases. The Big 40 from the early 90's were just a little bit better but not much. Not to discourage you but do a search about getting into pipeline work before you get your hopes up. It takes a lot of other work before it can happen if your just starting out.

Any SA 200. This forum has a section dedicated to that machine. Go and start working your way through all the issues that will arise with that welder. You need to be a good mechanic if you want to keep the repair bills down. There will be repairs. I am not a pipe welder. I would not consider testing until I had worked as a helper for a while to see how it's done in the real world, and to get a feel for the tools that will be needed. I have a '55 shorthood that I use for structural. I was blessed to be the third owner of this machine and I only paid $800 for it, all original,too. Now, I add the cheap welder with all the other stuff needed to come on a project and not beg tools, and I'm into the 5k range; and that doesn't count the truck. Pipe welders need WAY more tools to be considered competent. The welding machine is the second most important part of your business. The first is experience. It took me a year of hanging around here just to figure out what the hell an Arkansas bell hole was!! Mouth shut-ears open and it will come.

Jon