Hello, if you'd like to be a pipe liner i am assuming that you want to insulate and fit protective over-cladding onto industrial pipes and heating systems etc? I helped an individual start his own business in the UK in 2008 and he now employs several others and does well from it.
You can line pipes in glass wool with foil outer barrier, or with spray applied foam which is more popular now and then install metal outer protection, usually aluminum pop riveted together, I have seen it on rooftop ventilation ductwork with a rubber cloth over cover and wrapped in adhesive backed foil..
You can work for an HVAC installer company fitting ventilation ducting in new buildings and do a short HVAC course , other than that it is really just work experience which you can pick up quickly, you'll need to work on some big sites including new build offices and Hospitals and also industrial sites..
Two training certs to get are the IPAF Scissor lift certificate and the Cherry picker certificate, they will help a lot for you.
Here are a few companies in Milwaukee for you to contact, if you would like me to help you with applying I am here, just ask.