Discrimination method of welded steel pipe and seamless steel pipe

1. Metallography

The metallographic method is the main method to distinguish between welded steel pipe and seamless steel pipe. There is no welding material added to the high-frequency resistance welded steel pipe, so the welded seam in the welded steel pipe is very narrow. If the method of rough grinding and re-corrosion is used, the weld seam cannot be 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 steel pipe parent material. At this time, the metallographic method can be used to distinguish the welded steel pipe and the seamless steel pipe. In the process of identifying the two steel pipes, it is necessary to cut a small sample with a length and width of 40mm at the welding place, perform rough grinding, fine grinding, and polishing on it, and then put it under a metallographic microscope to observe the structure. Welded and seamless steel pipes can be accurately distinguished when ferrite and Widmanrite, base metal, and weld zone structures are observed

2. Corrosion method

In the process of using the corrosion method to distinguish welded steel pipes and seamless steel pipes, grinding should be carried out on the welded seams of the processed welded steel pipes. After grinding, the grinding marks should be visible, and then the end faces should be polished with sandpaper at the welding seams. And treat the end face with 5% nitric acid alcohol solution, if there is an obvious weld, it can prove that the steel pipe is a welded steel pipe. However, there is no significant difference in the end face of the seamless steel pipe after corrosion.

Properties of welded steel pipes

Because the welded steel pipe is processed by high-frequency welding, cold rolling, and other processes, it has the following properties.

First, the thermal insulation function is good. The degree of heat loss of welded steel pipe is relatively small, only 25%, which is not only conducive to transportation, but also reduces costs.

Second, it has waterproof and corrosion-resistant. In the process of project construction, there is no need to set up a separate pipe trench, but the steel pipe can be directly buried underground or underwater, thus reducing the construction difficulty of the project.

Third, it has impact resistance. Even in a low-temperature environment, the steel pipe will not be damaged, so its performance has certain advantages.

Properties of seamless steel pipes

Due to the high tensile strength of the metal material of the seamless steel pipe, its anti-destructive ability is stronger, and it has a hollow channel, so it can effectively transport fluid. It is its strong transport ability, so the corrosion resistance of seamless steel pipe is higher than that of welding. Steel pipe and its rigidity are relatively large. Therefore, the more loads the seamless steel pipe can carry, it can be widely used in projects with higher construction requirements.