Grey patches of varying sizes on the surface of galvanized seamless pipes are galvanizing color differences, a common technical challenge in the current galvanizing industry. This phenomenon is mainly related to trace elements contained in the steel pipe itself and the composition of the zinc bath. Such discoloration does not impair the anti-corrosion performance of the pipes and only causes visual differences in appearance.
Gradually prominent raised marks can be seen on the surface of every galvanized seamless pipe; these deposits are pure zinc. They form as molten zinc flows down the pipe wall and solidifies during cooling after the pipe is lifted out of the zinc pot.
Grinding and zinc spraying marks can be observed near both ends of each galvanized seamless pipe. During hot-dip galvanizing, pipes are secured on special steel frames and immersed in molten zinc together with the frames. Fastening points will leave indentations after galvanizing, which are then ground smooth and sprayed with zinc for a better appearance.
Some customers adopt grooved connections for galvanized seamless pipes on site. As hot-dip galvanized seamless pipes feature a thick zinc coating, partial cracking and peeling of the galvanized layer may occur under destructive external force. This issue bears no relation to the inherent quality of the galvanized seamless pipes.
Certain customers report yellow liquid residues on galvanized seamless pipes — this liquid is passivation solution, used for post-treatment of coatings such as zinc plating and cadmium plating. It forms a protective film on the metal surface to inhibit electrochemical reactions, boosting corrosion resistance and improving the aesthetic finish. It effectively enhances the pipe’s anti-corrosion capacity and extends the service life of workpieces.
2.Domestic seamless pipes supplied with hydrostatic test certification shall pass the pressure test specified in relevant specifications.
3.Mechanical property tests for imported seamless pipes shall be conducted in compliance with relevant standards agreed in the sales contract.
Precision seamless pipes are high-precision steel tubes processed via cold drawing or hot rolling. With oxide-free inner and outer walls, zero leakage under high pressure, high dimensional tolerance and surface smoothness, they resist deformation during cold bending and cracking during flaring or flattening. They are primarily used to fabricate pneumatic and hydraulic components such as air and hydraulic cylinders, and can be either seamless or welded tubes.
Compared with solid steel materials like round bars, seamless pipes deliver lighter weight while maintaining identical bending and torsional strength. As an economical structural section steel, they are widely used for structural components and mechanical parts. Precision seamless pipes retain all advantages of ordinary seamless pipes while possessing exclusive superior characteristics.
Precision manufacturing of annular components using precision seamless pipes improves material utilization, simplifies production procedures, and reduces raw material and machining costs. Typical products include rolling bearing races and jack sleeves, which are mass-produced from precision seamless pipes.
