Description

Longitudinal welded pipe refers to a steel pipe whose weld seam runs parallel to the longitudinal direction of the steel pipe. It is also commonly known as straight seam welded pipe or straight seam steel pipe. Longitudinal welded pipes are manufactured by rolling long steel strips of specified specifications through high-frequency welding units and performing straight seam welding. The specifications of longitudinal welded pipes are indicated by nominal diameter. By wall thickness, they are divided into thin-wall longitudinal welded pipes and thick-wall longitudinal welded pipes; by shape, they can be classified into round, square and special-shaped pipes.

### Classification by Weld Seam Shape
They can be divided into longitudinal welded pipes and spiral welded pipes.

**Longitudinal Welded Pipe**: It features simple production technology, high production efficiency, low cost and rapid development.

**Spiral Welded Pipe**: It generally has higher strength than longitudinal welded pipes. It can produce large-diameter welded pipes from narrower raw materials, and can also manufacture welded pipes of different diameters using raw materials of the same width. However, compared with longitudinal welded pipes of the same length, its weld seam length increases by 30% to 100%, and the production speed is lower. Therefore, small-diameter welded pipes mostly adopt straight seam welding, while large-diameter welded pipes mostly use spiral welding.

### Classification by Usage
Welded pipes are categorized by application into general welded pipes, galvanized welded pipes, oxygen-blowing welded pipes, electrical conduit pipes, metric welded pipes, idler pipes, deep well pump pipes, automotive pipes, transformer pipes, electric welded thin-wall pipes, electric welded special-shaped pipes and spiral welded pipes.

**General Welded Pipe**: General welded pipes are used for conveying low-pressure fluids. They are made of Q195A, Q215A and Q235A steel, and can also be made of other weldable mild steel. The steel pipes need to undergo hydraulic pressure, bending, flattening and other tests with certain requirements on surface quality. The usual delivery length is 4-10 meters, and fixed-length or multiple fixed-length delivery is often required. The specifications of welded pipes are marked by nominal diameter (in millimeters or inches), and the nominal diameter differs from the actual outer diameter. According to the specified wall thickness, welded pipes are divided into standard steel pipes and reinforced steel pipes; by pipe end form, they are classified into threaded end pipes and non-threaded end pipes.