I use cheap metal pipes, like bronze, invar, steel. Depends on what is reasources are more available at current world. I use quite many stainless steel tanks and mass storages - nothing flammable in a factory. Distilled water tank (from stainless steel) is like a “base”, to which I attach machines through distilled water and return pipe. Steam pipes are usually 0, 1 or 2 pipes long, often with pressure valve. What else to say… when I don’t know what to do, I make more stainless steel 
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