Piping

A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids.

There are few processes for metallic pipe manufacture: 

Seamless (SMLS) pipe is formed by drawing a solid billet over a piercing rod to create the hollow shell in a process called rotary piercing. As the manufacturing process does not include any welding, seamless pipes are perceived to be stronger and more reliable.

Welded pipe is formed by rolling plate and welding the seam usually by Electric resistance welding "ERW". ERW pipes are manufactured from the longitudinal welding of steel. The welding process for ERW pipes is continuous, as opposed to welding of distinct sections at intervals. ERW process uses steel coil as feedstock.

Large-diameter pipe (25 centimetres or greater) may be longitudinal-submerged arc-welded (LSAW) pipe. LSAW are made by bending and welding wide steel plates and most commonly used in oil and gas industry applications.

Typically metallic piping is made of steel or iron, such as unfinished, black (lacquer) steel, carbon steel, stainless steel, galvanized steel, brass, and ductile iron.