Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip after curling and forming, and generally Sizes 6 meters. Welded steel pipe has the advantages of simple production process, high production efficiency, more varieties and specifications, less equipment investment, but its general strength is lower than seamless steel pipe. It is also divided into general welded pipe, galvanized welded pipe, oxygen blowing welded pipe, wire sleeve, metric welded pipe, idler pipe, deep well pump pipe, automobile pipe, transformer pipe, welded thin-walled pipe, welded special-shaped pipe, scaffold pipe and spiral welded pipe. General welded pipe: General welded pipe is used to transport low-pressure fluid. Made of Q195A, Q215A and Q235A steel. It can also be made of other soft steels which are easy to weld. In order to carry out hydraulic, bending and flattening experiments on steel pipes, there are certain requirements for surface quality. Usually the delivery length is 4-10m, and the delivery of steel pipes is usually required to be of fixed size (or double size). The specification of welded pipe is different from the actual one in nominal diameter (millimeter or inch). There are two kinds of welded pipe according to the prescribed wall thickness: ordinary pipe and thick pipe. The pipe is divided into threaded and non-threaded according to the end form. Galvanized steel pipes: In order to improve the corrosion resistance of steel pipes, galvanized common steel pipes (black pipes). Galvanized steel pipes are divided into hot-dip galvanizing and electro-galvanizing. Hot-dip galvanizing has thick galvanizing layer and low galvanizing cost. Oxygen-blowing welded pipe: used as steel-making oxygen-blowing pipe, generally with small-caliber welded steel pipe, specifications from 3/8 inch to 2 inch eight kinds. It is made of 08, 10, 15, 20 or Q195-Q235 steel strips. In order to prevent corrosion, some are aluminized. Wire sleeve: that is, ordinary carbon steel welded steel pipe, used in concrete and various structural distribution projects, commonly used nominal diameter from 13 to 76 mm. The sleeve wall of wire sleeve is thin, and most of them are used after coating or galvanizing, so cold bending test is required. Metric welded pipes: welded pipes in the form of seamless pipes, expressed in millimetres of outer diameter and wall thickness, are welded in hot and cold zones of common carbon steel, high quality carbon steel or general energy low alloy steel, or are welded in hot zones and then made by cold dialing method. Metric welded pipes are commonly used as structural parts, such as transmission shafts, or conveying fluids, and thin-walled pipes are used to produce furniture, lamps, etc. The strength and bending test of steel pipes should be guaranteed. Roller pipe: Used for welding steel pipe of belt conveyor roller. It is generally made of Q215, Q235A, B steel and 20 steel with diameter of 63.5-219.0mm. There are certain requirements for pipe bending, end face to be perpendicular to the center line and ellipticity. Generally, hydraulic and flattening tests are carried out.