The appearance defects of the welded pipe include long knife bend, wavy bend, gnawing edge, scab, scratch, embossing, uneven head and tail, tower-shaped roll, loose roll, surface oxide skin, etc.

Rectangular tube is a name for square tube and rectangular tube (such as a500 square tube and a500 rectangular tube), that is, steel tubes with equal and unequal side lengths. It is made of strip steel after process treatment. Generally, the strip steel is unpacked, flattened, crimped, welded to form a round tube, and then rolled into a square tube from the round tube and then cut to the required length.

Steel pipes (such as seamless pipes and welded pipes) are easily rusted or even completely damaged in air, water or soil. Annual steel loss due to corrosion accounts for about 1/10 of the entire steel production. On the other hand, the surface of steel pipes and parts has certain special functions, and at the same time gives them a decorative appearance, so they are generally treated by galvanizing.

Square rectangular tubes (such as a500 square tube or a500 rectangular tube) are often bent, elliptical or partially bruised due to improper loading, unloading, handling or storage. It must be processed during installation to make it meet the standard of use. The square rectangular tube should carefully check the deformed part and analyze the cause of the deformation before processing.

The steel pipe pile is composed of a steel pipe, a tongue and groove, and a tongue and groove pin. The left end pipe wall of the steel pipe diameter is vertically connected with a rebate groove, and the cross section of the rebate groove is a square frame shape with one side opening, and a reinforcing rib is provided on the side of the rebate groove.

In the manufacture of seamless steel, there are many reasons to make the steel pipe magnetic, and the main reasons for the residual magnetism of the steel pipe are process magnetism and induced magnetism.