I've come up with quite a few bad ideas on this, and now I need some good ones... here's the deal: Our shop is pre-fabricating some pipe rack modules for a laboratory. Each module has several different types of pipe: carbon steel, copper, and polypropylene, ranging in size from 3" to 1/2". Once the modules are joined together in the field, any leaks are going to be hard to get to and repair, so the idea is to test what we can in the shop using compressed air at 15-20 lbs before they go out. The problem is that the pipes either have plain ends or socket-type fittings on the ends. I can't think of any good way to "stop up" the ends so I can get an air test on them without damaging the ends of the pipe. I'd rather not solder or braze stub ends onto the copper. Fernco fittings can't take the air pressure. I've even though about running to Home Depot and getting Sharkbite fittings, but it looks like they don't run larger than 3/4" or 1".

Ideas? How can I test at 15-20 lbs., keep things relatively clean-looking, and not end up making a gauge launcher?