Galvanized pipe, also known as galvanized steel pipe, is divided into two types: hot-dip galvanized and cold-dip galvanized pipe. Hot-dip galvanized galvanized layer is thick, and has the advantages of uniform coating, strong adhesion and long service life. The cost of cold-dip galvanized pipe is low, the surface is not very smooth, and its corrosion resistance is much worse than that of hot-dip galvanized pipe.

Pores in welded seam of welded steel pipe not only affect the tightness of pipe weld and cause pipe leakage, but also become the induction point of corrosion, which seriously reduces the strength and toughness of weld.

The so-called bright heat treatment includes bright annealing, bright normalizing, bright quenching and bright tempering. In order to prevent oxidation and decarburization of the surface of the stainless steel seamless pipe so that it does not lose its metallic luster, heat treatment should be carried out in a protective atmosphere or vacuum as mentioned above.

The size defects of seamless pipes include uneven wall thickness, excessive wall thickness, excessive outer diameter, bending

Spiral steel pipe (SSAW steel pipe) is a welded steel pipe made by rolling low-carbon carbon structural steel or low-alloy structural steel strip into a tube blank at a certain helical angle (called forming angle), and then welding the pipe seams.

Large-diameter welded pipes generally use double-sided submerged arc welding welded steel pipes, which can be divided into large-diameter straight seam welded pipes and large-diameter spiral welded pipes according to their weld seams.