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ERW pipe is divided into many different kinds. Following is their difference and various usage.

Welded steel pipe: also known as pipe, it is made by bending steel sheet or strip, and then welded. According to the weld form it is divided into Longitudinal and spiral pipe.
By end-use it is divided into general pipe, galvanized pipe, oxygen lance pipe, wire casing, metric pipe, roller pipe, deep well pump tubes, automobile tubes, transformers pipes, welding thin-walled tube, welding shape tube and spiral welded pipe.

1> General pipe: General pipe are used to transport low pressure fluid, we also call it black pipe. Material is almost of Q195A, Q215A, Q235A. Or some other easily welded mild steel. Pipes must be conducted the experiment of the pressure, bending, flattening and surface quality. Generally the delivery length is 4-10m, and often be required to deliver special length (or double length). Specifications of welded pipe with nominal diameter (millimeters or inches) are different with the actual. As to the wall thickness of pipe, there are ordinary steel pipe and thicker steel pipe. By the form of pipe end, there are sub-threaded and threaded. With the technology of welded steel pipe to improve and processing be more simply, some welded pipe can replace part of the seamless pipe. And we can produce pipes of outer diameter up to 219mm (8 inch) right now.

2> Galvanized steel pipe: in order to improve the corrosion resistance of steel pipes, we always coat some zinc on the surface of general steel pipe, that is galvanized pipe. There are two division of galvanized pipes: hot-dipped and electro-galvanized. The zinc coating of hot-dipped galvanized is thicker than electrical. But the latter is less cost.

3> Blowing Oxygen: The pipe is used for blowing Oxygen in steelmaking. generally are small diameter pipes. And sizes are almost eight kinds from 3/8 inch to 2 inch. Material are almost 08,10,15,20 or Q195 AT-of Q235. For corrosion resistance, some pipes are aluminized.

4> Electric wire conduit: Generally it is common welded carbon steel pipe and used in concrete and a variety of structure and distribution projects. The nominal diameter are from 13mm to 76mm. The wall thickness is thin and mostly coated or galvanized. And cold bending test has been requested.

5> Metric pipe: The specifications are always the same with seamless pipe, that is OD*wall thickness(mm), Material are almost of ordinary carbon steel, quality carbon steel or general tropical low-alloy steel. Welding or cold-drawing after welding. Metric pipe are divided into ordinary used and thin-wall. Ordinary used pipes are used as structural components, such as drive shafts and transmission fluid. Thin-wall pipes are used in the production of furniture and lamps, etc., But it has to ensure the strength and bending tests of the steel pipe.

6> Roller tube: The roller tube is used for belt conveyor, usually the material are Q215, Q235A, B-grade steel and 20# steel. Diameter are from 63.5mm to 219.0mm. It has certain requirements curvature, end perpendicular to the centerline and ellipticity. Always it should be conducted the general pressure and flattening test.

7> Transformer tube: The transformer tube is used for transformer cooling pipes and other heat exchangers, material is almost ordinary carbon steel. The tubes should be conducted the flattening, flaring, bending, and hydraulic test. Transformer tubes are required to cut to length or double length delivery, there are certain requirements for curvature of tubes.

8> Shaped tubes: The material are almost ordinary carbon structural steel or 16Mn. Shapes are always square, rectangular, cap and tubes for doors and windows. The shaped tubes are mainly used for agricultural components and steel window and door.

9> Welding thin-walled tube: Welding thin-walled tube is mainly used to make furniture, toys, lamps, etc.. In recent years, the applications of stainless thin-walled tubes is very wide range, like fine furniture, decorative material and fence.

10> Spiral welded steel pipe: Spiral welded pipe is produced to roll the low-carbon structural steel or low alloy steel strip according to the angle of the spiral line (called the forming angle) rolled into the tube and then welded together, It can produce large diameter steel pipe by narrow strip. Spiral welded pipe is mostly used for oil and gas pipelines, Its specification is always of OD * wall thickness. There are two welding forms of spiral welded pipes, that is one-sided and double-sided welding. the pipe should be conducted test of hydrostatic, the weld tensile strength and cold bending performance.