Steel pipes are long, hollow tubes that are used mainly to convey products from one location to another. They are produced mainly by two distinct manufacturing methods which result in either a welded pipe or seamless pipe. In both the manufacturing methods, raw steel is first cast into a more workable starting form (slabs, hot billet or flat strip). It is then made into a pipe by stretching the hot steel slab/billet out into a seamless pipe or forcing the edges of flat steel strip together and sealing them with a weld.

When operational conditions require high wall thickness due to high internal or external pressures, LSAW (Longitudinal Submerged Arc Welding) pipes are commonly the most economical solution.

The LSAW pipe diameter range is larger than ERW (Electric resistance welding), normally from 16 inch (406 mm) to 60 inch (1500 mm). Good performances on high pressure resistance, and low-temperature corrosion resistance.

In LSAW pipe mills, processing is carried out by cold forming heavy carbon steel plates, the pipe pre‐material on which many of the pipe properties depend.

The material of LSAW steel pipe is unit middle or heavy thickness sheet, coiled in the molding or forming machine, welded by double submerged arc welding and expand the diameter. The specification scope is wide, and have good toughness, ductility, uniformity, compactness, etc.

Longitudinal submerged arc welded (LSAW) pipes manufacture process is bending and welding wide steel plates to pipes from leveled hot rolled coils by both the JCOE and UOE (the forming process in which the plate like the letter “J”, “C”, “O” or “U” shape, then expansion) forming processes.

In Figure 1 is shown a UOE method for production of longitudinally welded large diameter pipes. Longitudinally edges of steel plates are first beveled using carbide milling equipment. Beveled plates are then formed into a U shape using a U-press subsequently into an O shape using an O-press.

Figure 1: Longitudinal seam Submerged Welded (LSAW) pipes with UOE process

Inspection: Chemical Component Analysis, Mechanical Properties (Ultimate tensile strength, Yield strength, Elongation), Technical Properties (Flattening Test, Bending Test, Blow Test, Impact Test), Exterior Size Inspection, Hydrostatic Test, X-ray Test. Application of LSAW Steel Pipe: The tubes are mainly used for oil, natural gas, gas, central heating, water supply, sewage treatment, low-pressure fluid delivery and so on.