Steel pipes are sometimes lined with material which can withstand chemical attack of highly corrosive fluids. Lined pipes are supplied with pre-welded flanges. For lined piping network, fittings are also flanged.
Linings (rubber, for example) can be applied after fabricating the piping, but pipe is often pre-lined, and manufacturers give instructions for making joints.
Linings of various rubbers, plastics, metals and vitreous (glassy) materials are available. Polyvinyl chloride, polypropylene and copolymers are the most common coating materials.
Rubber lining is often used to handle abrasive fluids.
Carbon-steel pipe zinc-coated by immersion into molten zinc (hot-dip galvanized) is used for conveying drinking water, instrument air and various other fluids.