1. Metallographic method:
The metallographic method is the main method to distinguish welded steel pipes and 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 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 welded steel pipes and seamless steel pipes. In the process of identifying the two steel pipes, it is necessary to cut a sample with a length and width of 40mm at the welding joint, rough grinding, fine grinding, and polishing, and then place it under a metallographic microscope to observe the structure. When the ferrite and Widmansite, base metal, and weld zone structures are observed, welded steel pipes and seamless steel pipes can be accurately distinguished.
2. Corrosion method:
In the process of using the corrosion method to identify welded steel pipes and seamless steel pipes, the welding seams of the processed welded steel pipes should be polished. After the grinding is completed, the traces of grinding should be visible, and then the end faces of the welded seams should be polished with sandpaper. And use 5% nitric acid alcohol solution to treat the end face. 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 seamless steel pipe after corrosion.
Properties of welded steel pipes: Welded steel pipes have the following properties they are processed by high-frequency welding, cold rolling, and other processes.
First, the thermal insulation function is good. The heat loss of welded steel pipes is relatively small, only 25%, which not only facilitates transportation but also reduces costs.
Second, it is waterproof and corrosion-resistant. During the construction process, there is no need to set up a separate pipe trench. The steel pipe can be directly buried underground or underwater, thus reducing the difficulty of construction.
Third, it has impact resistance. Even in low-temperature environments, steel pipes will not be damaged, so their performance has certain advantages.
Performance of seamless steel pipe: Because the metal material of seamless steel pipe has high tensile strength, it has stronger resistance to damage, and it has hollow channels, so it can effectively transport fluids. It is its strong transport capacity that makes seamless steel pipes The corrosion resistance is higher than that of welded steel pipes, and its stiffness is relatively high. Therefore, seamless steel pipes can carry more loads and can be widely used in projects with higher construction requirements.
3. Distinguish between 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, welded steel pipes are welded according to cold rolling, extrusion, and other processes. In addition, when welding steel pipes using high-frequency, low-frequency arc welded pipes and resistance welded pipe processes, there will be The formation of spiral pipe welding and straight seam pipe welding will form circular steel pipes, square steel pipes, oval steel pipes, triangular steel pipes, hexagonal steel pipes, rhombus 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 process, they are mainly distinguished based on hot-rolling and cold-rolling processing methods, and seamless steel pipes mainly come in two forms, namely hot-rolled seamless steel pipes and cold-rolled seamless steel pipes. Hot-rolled seamless steel pipes are formed through processes such as perforation and rolling. Large-diameter and thick seamless steel pipes are welded using this process; cold-drawn pipes are cold-drawn from tube blanks, and the strength of the material is lower. , but its exterior and internal control surfaces are smooth.
4. Distinguish welded steel pipes and seamless steel pipes according to their uses
Welded steel pipes have higher bending and torsional strength and greater load-bearing capacity, so they are generally widely used in the manufacturing 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 pipelines for transporting fluids because they have a hollow cross-section and are long strips of steel with no seams around them. For example, it can be used as a pipeline to transport oil, natural gas, coal gas, water, etc. In addition, seamless steel pipes have relatively low bending strength, so they are generally widely used in superheated steam pipes for low and medium-pressure boilers, boiling water pipes, and superheated steam pipes for locomotive boilers. In short, through the classification of uses, welded steel pipes and seamless steel pipes can be clearly distinguished.
To ensure higher quality of construction projects in our country, welded steel pipes and seamless steel pipes must be distinguished, and then appropriate steel pipes should be used for construction. In the process of identifying welded steel pipes and seamless steel pipes, metallographic methods, and corrosion methods can be used to observe the structure and welds to inspect the welds and finally accurately identify them. At the same time, the two steel pipes can also be distinguished based on their performance and uses, and then reasonable steel pipes can be selected for construction.
Post time: Sep-21-2023