1. Metallography
Metallography is one of the main methods for distinguishing welded steel pipes from seamless steel pipes. High-frequency resistance welded steel pipes do not add welding materials, so the weld seam in the welded steel pipe is very narrow. If the method of rough grinding and then corrosion is used, the weld seam cannot be clearly seen. Once the high-frequency resistance welded steel pipe is welded and has not undergone heat treatment, the weld structure will be essentially different from the parent material of the steel pipe. At this time, the metallographic method can be used to distinguish welded steel pipes from seamless steel pipes. In the process of distinguishing the two steel pipes, it is necessary to cut a small sample with a length and width of 40mm at the welding point, perform rough grinding, fine grinding and polishing, and then observe the structure under a metallographic microscope. When ferrite and widmanstatten, parent material and weld zone structure are observed, the welded steel pipe and seamless steel pipe can be accurately distinguished.
2. Corrosion method
In the process of using the corrosion method to distinguish welded steel pipes and seamless steel pipes, the weld of the processed welded steel pipe should be polished. After the polishing is completed, the polishing marks should be seen. Then, the end face is polished with sandpaper at the weld, and the end face is treated with 5% nitric acid alcohol solution. If an obvious weld appears, it can be proved that the steel pipe is a welded steel pipe. There is no obvious difference in the end face of the seamless steel pipe after corrosion.
3. Distinguish welded steel pipes and seamless steel pipes according to the process
In the process of distinguishing welded steel pipes and seamless steel pipes according to the process, all welded steel pipes are welded according to processes such as cold rolling and extrusion. In addition, when high-frequency, low-frequency arc welding pipes and resistance welding pipes are used to weld steel pipes, spiral pipe welding and straight seam pipe welding will be formed, which will form round steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, wilted steel pipes, octagonal steel pipes, and even more complex steel pipes. In short, different processes will form steel pipes of different shapes, so that welded steel pipes and seamless steel pipes can be clearly distinguished. However, in the process of distinguishing seamless steel pipes according to the process, they are mainly distinguished according to the hot rolling and cold rolling treatment methods, and seamless steel pipes also have two main forms, namely hot-rolled seamless steel pipes and cold-rolled seamless steel pipes. Hot-rolled seamless steel pipes are formed by perforation, rolling and other processes, especially large-diameter and thick seamless steel pipes are welded by this process; cold-drawn pipes are formed by cold drawing of pipes, and the strength of the material is lower, but its outer and inner surfaces are smooth.
Post time: May-17-2024