The pipe material in a compressed air network affects pressure drop, leaks and corrosion over the life of the system. A cheap material that corrodes or leaks costs far more in energy and repairs than the initial saving.
Galvanised steel
Steel pipe is strong and widely available, and threaded fittings are familiar to installers. However, threads leak over time, and internal corrosion roughens the bore and increases pressure drop. It is a workable choice for small, simple systems but not the best for long or large networks.
Aluminium
Aluminium systems use smooth, corrosion-resistant tube with push-in fittings. The smooth bore keeps pressure drop low for the life of the system, and installation is fast and leak-resistant. The material costs more than steel but pays back in lower energy and fewer leaks.
Polymer systems
Engineered polymer or stainless-lined systems offer similar smooth-bore benefits with rapid assembly. They suit clean applications and retrofit work. Whatever the material, size the pipe for total flow and use a looped layout with drains at low points.