Welded steel pipe, also known as welded pipe, is a steel pipe made of steel plate or strip steel after crimping and welding. Welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe.Commonly used materials for welded pipes are: Q235A, Q235C, Q235B, 16Mn, 20#, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, etc.

Carbon steel welded pipe classification method:

Welded steel pipes are classified according to the form of the weld: straight seam welded pipe and spiral welded pipe.

The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with a larger diameter can be produced with a narrower billet, and welded pipes with different diameters can be produced with the same width billet. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower. 

Welded pipes with smaller diameters adopt straight seam welding, and welded pipes with large diameters mostly use spiral welding; according to the shape of the end of the steel pipe, it is divided into circular welded pipe and special-shaped (square, rectangular, etc.) welded pipe; according to different materials and uses, it is divided into mine fluid Conveying welded steel pipes, galvanized welded steel pipes for low-pressure fluid transportation, electric welded steel pipes for belt conveyor rollers, etc. According to the specification and size table in the current national standard, they are sorted by outer diameter * wall thickness from small to large. 

Classified by production method: arc welded pipe, electric resistance welded pipe, (high frequency, low frequency) gas welded pipe, furnace welded pipe.

Generally welded pipes are made of Q195A, Q215A, Q235A steel. It can also be manufactured from other mild steels that are easy to weld. Steel pipes are subject to water pressure, bending, flattening and other tests, and have certain requirements for surface quality. Usually, the delivery length is 4-10m, and it is often required to deliver in fixed length (or double length). The specification of the welded pipe is represented by the nominal diameter (mm or inch). The nominal diameter is different from the actual one. The welded pipe has two types of ordinary steel pipe and thickened steel pipe according to the specified wall thickness. The steel pipe is divided into two types: threaded and unthreaded according to the pipe end form.

Welded steel pipe standards and types: