Surface processing defects of seamless tubes and their prevention

 Surface processing of seamless tubes (smls) mainly includes: steel tube surface shot peening, overall surface grinding and mechanical processing. Its purpose is to further improve the surface quality or dimensional accuracy of steel tubes.

Shot peening on the surface of seamless tube: Shot peening on the surface of steel pipe is to spray iron shot or quartz sand shot (collectively referred to as sand shot) of a certain size on the surface of seamless tube at a high speed to knock off the oxide scale on the surface to Improve the smoothness of the steel tube surface. When the iron oxide scale on the surface of the steel tube is crushed and peeled off, some surface defects that are not easy to be found by the naked eye will also be exposed and easy to remove.

The size and hardness of the sand shot and the injection speed are important factors affecting the shot peening quality of the steel tube surface. If the sand shot is too large, the hardness is too high and the injection speed is too fast, it is easy to crush and fall off the oxide scale on the surface of the steel tube, but it may also cause a large number of pits of different sizes on the surface of the steel tube to form pockmarks. On the contrary, the iron oxide scale may not be completely removed. In addition, the thickness and density of the oxide scale on the steel tube surface will also affect the shot peening effect.

The thicker and denser the iron oxide scale on the steel tube surface, the worse the effect of iron oxide scale cleaning under the same conditions. Spray (shot) shot derusting is the most ideal way for pipeline derusting.

Overall grinding of the surface of seamless tube: The tools for overall grinding of the outer surface of the steel pipe mainly include abrasive belts, grinding wheels and grinding machines. The overall grinding of the inner surface of the steel pipe adopts grinding wheel grinding or inner mesh grinding machine grinding. After the surface of the steel tube is ground as a whole, it can not only completely remove the oxide scale on the surface of the steel tube, improve the surface finish of the steel tube, but also remove some small defects on the surface of the steel tube, such as small cracks, hairlines, pits, scratches, etc. Grinding the surface of steel tube with abrasive belt or grinding wheel as a whole may cause quality defects mainly: black skin on the surface of steel tube, excessive wall thickness, plane (polygon), pit, burns and wear marks, etc. The black skin on the surface of the steel tube is due to the small amount of grinding or pits on the surface of the steel tube. Increasing the amount of grinding can eliminate the black skin on the surface of the steel tube.

Generally speaking, the surface quality of the steel pipe will be better, but the efficiency will be lower if the seamless steel tube is ground with the abrasive belt as a whole.

https://www.xysteelpipe.com/surface-processing-defects-of-seamless-tubes-and-their-prevention/