1. Metallographic method
Metallographic method is one of the main methods to distinguish welded steel pipes from seamless steel pipes. High-frequency resistance welded steel pipes do not have welding materials added, 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 been heat treated, 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, and perform rough grinding, fine grinding and polishing on it, 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, and then the end face is polished with sandpaper at the weld, and the end face is treated with 5% nitric acid alcohol solution. If there is an obvious weld, 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.
Structural Carbon Steel Tubes
