Welded pipe production process:
Welded pipe, also known as welded steel pipe, is a steel pipe made by applying welding technology to roll steel plate or strip into a tube shape, and then flattening, crimping, welding and leveling.
Generally, the production process of welded pipes is divided into three processes: hot rolling, cold rolling and cold drawing. Among them, hot-rolled welded pipes are welded by hot-rolling steel strips at high temperatures, while cold-rolled welded pipes are welded by cold-rolling steel strips at room temperature. The cold drawn welded pipe is made by cold drawing process after welding.
Materials and characteristics of welded pipes:
The raw materials of welded pipes are mostly black steel plates (
black steel pipe), whose main components are carbon and manganese. During the welding process, the composition of the welded joint changes, and carbon and other elements undergo chemical reactions. Therefore, the welded area is usually more susceptible to corrosion than the non-welded area.
Welded pipes are widely used because of their light weight, low price, high strength, and easy processing. However, due to changes in the welding process and the influence of the pipe composition, the physical properties of welded pipes sometimes have certain deficiencies.
The difference between cold rolling and hot rolling of welded pipes:
1. Cold rolling
Cold rolling refers to a steel pipe made by rolling a black steel plate into a tube shape at room temperature and performing processes such as forming, welding, leveling, trimming, edge closing and trimming. Because it is processed at room temperature, its processing accuracy is high and the toughness and stretchability of the material will not be reduced due to processing, so the cold-rolled welded pipe also has good strength and toughness. However, the production process of cold-rolled welded pipes is slow and the cost is relatively high. Cold rolling is generally used to manufacture steel pipes for low-pressure fluid transportation, such as water pipes.
2. Hot rolling
Hot rolling is a process processed at high temperatures. At high temperatures, steel has good plasticity and plasticity and can quickly adapt to millisecond-level deformations. Therefore, hot rolling can produce thick-walled welded pipes with a smooth surface. However, processing at high temperatures will cause changes in the crystal structure of the material, resulting in a decrease in fracture toughness and limited processing accuracy. Hot rolling is usually used to manufacture high-pressure pipelines, such as oil pipelines, natural gas pipelines, etc.
Application scope of hot rolling and cold rolling:
Due to its fast production speed and smooth surface, hot rolling has a wide range of applications. Hot-rolled welded pipes are commonly used in construction, machinery, petroleum and chemical industries.
Due to its good strength and deviation, cold-rolled welded pipe is usually used to manufacture high-precision parts, such as automobiles, electrical appliances, precision instruments and other fields.
The difference in weldability between hot-rolled pipes and cold-rolled pipes:
a. Weldability of hot rolled pipes
Hot-rolled pipes are made by heating a steel billet to change it from a solid state to a plastic state, and then rolling and forming it. After the hot-rolled pipe is formed, some changes will occur inside and on the surface. These changes have a great impact on the weldability of the pipe.
Since there will be certain grain boundaries and defects inside and on the surface of hot-rolled pipes, these factors will aggravate the cracking of the weld bead during welding of hot-rolled pipes. In addition, damage and deformation of hot-rolled pipes will also affect their weldability. Therefore, when welding hot-rolled pipes, it is necessary to strengthen preheating and heat treatment to ensure the quality and stability of the weld.
b. Weldability of cold-rolled pipes
Cold-rolled pipes are made by rolling and drawing steel plates multiple times. The overall hardness of cold-rolled pipes is relatively high and the metallurgical structure is relatively stable. Therefore, the weldability of cold-rolled pipes is better than that of hot-rolled pipes.
In addition, the surface of the cold-rolled pipe is smooth and scratch-free, retaining the anisotropy and ductility of the steel plate, which is beneficial to processing and operation during welding. Therefore, using cold-rolled pipes for welding can achieve better welding quality and avoid hot cracking.
Conclusion:
Welded pipes are both hot-rolled and cold-rolled, each with its own characteristics and application scope. For different fields and needs, different welded pipe processes can be selected according to actual conditions. The weldability of hot-rolled pipes and cold-rolled pipes is different and needs to be selected and processed according to specific conditions. In practical applications, attention needs to be paid to the reasonable selection of pipe materials and processes to avoid poor welding quality.
