Hi centurion, I made my back wheels from heavy gauge boiler pipe, the front wheels are made from scrap steam turbine nuts which I machined down to size. The boiler is made from proper boiler tube from the power plant I used to work in . I increased the wall thickness to almost 1/4" and made the plates etc slightly thicker as well. Unfortunately as I am not a coded welder I cannot get anyone to give me a boiler certain as the laws here are very strict also . It's my fault as I should have looked into this more. In am a very good tig welder, having been taught by coded pressure welders and the boiler is a really fine thing that I have pressure tested to 200 psi with no problems and no leaks so I am confident it is ok for my own private use , it's just a bit frustrating! But the law is the law and I am well aware of what steam can do , being a steam turbine technician. I cannot for the life of me think how a a copper boiler soldered together in some ones workshop can be considered better or stronger than a correctly welded steel one , apart from the corrosion problems . I dare say mine will become a nice ornament in my front room !