Here is the method of distinguishing welded steel pipe and seamless steel pipe shared by the Welded Steel Pipe Supplier. I hope it will be helpful to everyone.
Metallographic method is one of the main methods to distinguish welded steel pipes and seamless steel pipes. High-frequency resistance welded steel pipes do not add welding materials, so the welds in the welded steel pipes are very narrow, and the welds cannot be clearly seen if the method of rough grinding and re-corrosion is used. Once the high-frequency resistance welded steel pipe has been welded without 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 and seamless steel pipes. In the process of distinguishing the two steel pipes, it is necessary to cut a sample of 40mm in length and width at the welding place, and perform rough grinding, fine grinding and polishing on it, and then place it under a metallurgical microscope to observe the structure. When observing the structure of ferrite and Widmanstatite, the base metal and the weld zone, the welded steel pipe and the seamless steel pipe can be accurately distinguished.
Welded Steel Pipe
In the process of distinguishing welded steel pipes and Seamless Steel Pipes by the corrosion method, the welds of the welded steel pipes should be polished. After the polishing is completed, the polished traces should be visible, and then the end faces of the welds should be polished with sandpaper. Treat the end face with a 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 between the end faces of seamless steel pipes after corrosion.
Since welded steel pipes are processed by high-frequency welding, cold rolling and other processes, they have the following properties.
First, the heat preservation function is good. The degree of heat loss of welded steel pipes is relatively small, only 25%, which is not only conducive to transportation, but also reduces costs.
Second, it has water resistance and corrosion resistance. During the construction of the project, there is no need to set up a separate pipe trench, just bury the steel pipe directly underground or underwater, thereby reducing the difficulty of the construction 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.
Due to the greater tensile strength of the seamless steel pipe metal material, its anti-destructive ability is stronger, and it has a hollow channel, so it can effectively transport fluid. It is its strong transport capacity, so the corrosion resistance of seamless steel pipe is higher than that of welding. Steel pipe, and its rigidity is relatively large. Therefore, the more the load carried by the seamless steel pipe, it can be widely used in projects with higher construction requirements.
In the process of distinguishing Welded Steel Pipes and seamless steel pipes according to the process, the welded steel pipes are welded according to the cold rolling, extrusion and other processes. In addition, when the steel pipe is welded by the high-frequency, low-frequency arc welded pipe and electric resistance welded pipe process, the formation of spiral pipe welding and straight seam pipe welding will form round steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, diamond steel pipes, octagonal steel pipes, and even more complex steel pipes. In short, using 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 identifying seamless steel pipes according to the process, the distinction is mainly based on the hot-rolled and cold-rolled processing methods, and there are two main forms of seamless steel pipes, namely hot-rolled seamless steel pipes and cold-rolled seamless steel pipes. Hot-rolled seamless steel pipes are formed by piercing, rolling and other processes, especially large diameter and thickness seamless steel pipes are welded by this process; cold-drawn pipes are formed by cold-drawn pipe blanks, and the strength of the material is lower , But its appearance and internal control surface are smooth.
Welded steel pipes have higher bending and torsion resistance and greater load-bearing capacity, so they are generally widely used in the manufacture of mechanical parts. For example, oil drill pipes, automobile drive shafts, bicycle frames, and steel scaffolding used in construction are all made of welded steel pipes. However, seamless steel pipes can be used as pipes for conveying fluids because they have a hollow cross-section and a long strip of steel without joints on the periphery. For example, it can be used as a pipeline to transport oil, natural gas, gas, water, etc. In addition, the bending strength of seamless steel pipe is relatively small, so it is generally widely used in low and medium pressure boiler superheated steam pipe, boiling water pipe and locomotive boiler superheated steam pipe. In short, through the classification of applications, welded steel pipes and seamless steel pipes can be clearly distinguished.
In order to ensure a higher quality of engineering construction in our country, it is necessary to distinguish between welded steel pipes and seamless steel pipes, and then use suitable steel pipes for construction. In the process of distinguishing welded steel pipes and seamless steel pipes, metallographic methods and corrosion methods can be used to inspect the welds by observing the structure and welds, and finally accurately distinguish them. At the same time, the two kinds of steel pipes can be distinguished according to their performance and purpose, and then a reasonable steel pipe can be selected for construction.
