Stainless steel has good comprehensive performance and good appearance and surface characteristics, and is widely used in various industries. Similarly, stainless steel pipes are no exception. Stainless steel pipe is a kind of steel with a hollow section, generally divided into stainless steel seamless pipe and welded pipe.There are also certain differences in their processing methods and performance, the differences are as follows:
1. The difference in the production process
The stainless steel welded pipe is welded by steel plate or steel strip after crimping and forming by the machine unit and mold, and there is generally a weld seam on the inner wall of the pipe. The stainless steel seamless pipe is made of round pipe billet as raw material for perforation, and is made by cold rolling, cold drawing or hot extrusion production process, and there is no welding point on the pipe.
2. The difference in the appearance of steel pipes
The stainless steel welded pipe has a very small wall thickness tolerance, and the wall thickness of the entire circumference is very uniform; the steel pipe has high precision, the inner and outer surfaces of the pipe have high brightness, and can be arbitrarily scaled; thin-walled pipes can be made. The steel pipe of the seamless pipe has low precision, uneven wall thickness, low brightness of the inner and outer surfaces of the pipe, high cost of sizing, and there are pits and black spots on the inner and outer surfaces that are not easy to remove. Therefore, the walls of seamless pipes usually produced are thicker.
3. Differences in performance and price
Seamless pipes are much higher than welded pipes in terms of corrosion resistance, pressure resistance and high temperature resistance. With the improvement of the welded pipe manufacturing process, the mechanical properties and mechanical properties are gradually approaching the seamless pipe. The seamless pipe is more complicated in the manufacturing process, and its price is more expensive than the welded pipe.
Based on the characteristics and differences of stainless steel seamless pipes and welded pipes, reasonable selection should be made during application to achieve economical, beautiful and reliable results:
(1) When used as decorative pipes, product pipes, and prop pipes, it is generally required to have a good surface effect, and stainless steel welded pipes are usually used;
(2) For general low-pressure fluid transportation, such as low-pressure systems such as water, oil, gas, air, and heating hot water or steam, stainless steel welded pipes are usually used;
(3) Stainless steel seamless pipes should be used for pipes used in industrial engineering and large-scale equipment to convey fluids, as well as pipes for conveying fluids that require high temperature, high pressure and high strength on boilers in power plants and nuclear power plants:
(4) Stainless steel welded pipes are generally used for liquid transportation below 0.8MPa, and seamless pipes can be used for auxiliary transportation of liquids above 0.8MPa. If the pressure requirements are not high, it will be more economical to use welded pipes.
4. the advantages and disadvantages of stainless steel seamless pipe
(1) Advantages:
The forming speed is fast, the output is high, and it can be made into a variety of cross-sectional forms to meet the needs of the use conditions; cold rolling can cause large plastic deformation of the steel, thereby increasing the yield point of the steel. Hot rolling can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved.
(2) Disadvantages:
a. Metal stratification - when the steel pipe is cold-rolled, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and stratification (interlayer) occurs. Delamination greatly deteriorates the mechanical properties of steel along the thickness direction, and interlaminar tearing may occur when the welding strength expands.
b. Uneven wall thickness - the metal will expand with heat and contract with cold, because the cold-rolled steel pipe meets the standard even in length and thickness at the end of rolling. However, there will still be a certain negative difference after cooling. The greater the negative difference, the worse the uniformity of the wall thickness. Therefore, the wall thickness, length, straightness and ovality of the cold-rolled non-shrinkable boiler tube cannot be too correct.
c. Residual stress - Due to uneven cooling, steel pipes of various cross-sections have residual stress. The larger the cross-sectional size of the steel, the greater the residual stress, which has a certain impact on performance under the action of external force. For example, it may have adverse effects on deformation, stability, and anti-waste labor.
d. Poor surface finish - the inner surface of the steel pipe is longitudinally distributed, showing symmetrical or single linear folds, some of which exist all the way, and some exist locally.
5. Advantages of stainless steel welded steel pipe
(1) Uniform wall thickness - the base material is a formed strip, with good wall thickness consistency and high surface finish, reaching industrial clean surface level 2B
(2) Low residual stress - after forming, the steel pipe is bright annealed at a high temperature higher than 1040 degrees to eliminate stress.
(3) High welding seam strength - fusion welding is used for welding, and the material composition remains unchanged. After high temperature heat treatment, the weld seam and the base metal have the same intergranular structure. When performing destructive tests such as flattening, reverse bending, and flaring on the weld, there will be no problems such as cracking, cracking strength, and burrs at the weld. In addition, eddy current testing and water pressure or gas test are also required to ensure the quality of the pipe.
(4) Good consistency - the outer diameter, wall thickness, length and straightness of the pipe are consistent, and the processing precision is high.
1. The difference in the production process
The stainless steel welded pipe is welded by steel plate or steel strip after crimping and forming by the machine unit and mold, and there is generally a weld seam on the inner wall of the pipe. The stainless steel seamless pipe is made of round pipe billet as raw material for perforation, and is made by cold rolling, cold drawing or hot extrusion production process, and there is no welding point on the pipe.
2. The difference in the appearance of steel pipes
The stainless steel welded pipe has a very small wall thickness tolerance, and the wall thickness of the entire circumference is very uniform; the steel pipe has high precision, the inner and outer surfaces of the pipe have high brightness, and can be arbitrarily scaled; thin-walled pipes can be made. The steel pipe of the seamless pipe has low precision, uneven wall thickness, low brightness of the inner and outer surfaces of the pipe, high cost of sizing, and there are pits and black spots on the inner and outer surfaces that are not easy to remove. Therefore, the walls of seamless pipes usually produced are thicker.
3. Differences in performance and price
Seamless pipes are much higher than welded pipes in terms of corrosion resistance, pressure resistance and high temperature resistance. With the improvement of the welded pipe manufacturing process, the mechanical properties and mechanical properties are gradually approaching the seamless pipe. The seamless pipe is more complicated in the manufacturing process, and its price is more expensive than the welded pipe.
Based on the characteristics and differences of stainless steel seamless pipes and welded pipes, reasonable selection should be made during application to achieve economical, beautiful and reliable results:
(1) When used as decorative pipes, product pipes, and prop pipes, it is generally required to have a good surface effect, and stainless steel welded pipes are usually used;
(2) For general low-pressure fluid transportation, such as low-pressure systems such as water, oil, gas, air, and heating hot water or steam, stainless steel welded pipes are usually used;
(3) Stainless steel seamless pipes should be used for pipes used in industrial engineering and large-scale equipment to convey fluids, as well as pipes for conveying fluids that require high temperature, high pressure and high strength on boilers in power plants and nuclear power plants:
(4) Stainless steel welded pipes are generally used for liquid transportation below 0.8MPa, and seamless pipes can be used for auxiliary transportation of liquids above 0.8MPa. If the pressure requirements are not high, it will be more economical to use welded pipes.
4. the advantages and disadvantages of stainless steel seamless pipe
(1) Advantages:
The forming speed is fast, the output is high, and it can be made into a variety of cross-sectional forms to meet the needs of the use conditions; cold rolling can cause large plastic deformation of the steel, thereby increasing the yield point of the steel. Hot rolling can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved.
(2) Disadvantages:
a. Metal stratification - when the steel pipe is cold-rolled, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and stratification (interlayer) occurs. Delamination greatly deteriorates the mechanical properties of steel along the thickness direction, and interlaminar tearing may occur when the welding strength expands.
b. Uneven wall thickness - the metal will expand with heat and contract with cold, because the cold-rolled steel pipe meets the standard even in length and thickness at the end of rolling. However, there will still be a certain negative difference after cooling. The greater the negative difference, the worse the uniformity of the wall thickness. Therefore, the wall thickness, length, straightness and ovality of the cold-rolled non-shrinkable boiler tube cannot be too correct.
c. Residual stress - Due to uneven cooling, steel pipes of various cross-sections have residual stress. The larger the cross-sectional size of the steel, the greater the residual stress, which has a certain impact on performance under the action of external force. For example, it may have adverse effects on deformation, stability, and anti-waste labor.
d. Poor surface finish - the inner surface of the steel pipe is longitudinally distributed, showing symmetrical or single linear folds, some of which exist all the way, and some exist locally.
5. Advantages of stainless steel welded steel pipe
(1) Uniform wall thickness - the base material is a formed strip, with good wall thickness consistency and high surface finish, reaching industrial clean surface level 2B
(2) Low residual stress - after forming, the steel pipe is bright annealed at a high temperature higher than 1040 degrees to eliminate stress.
(3) High welding seam strength - fusion welding is used for welding, and the material composition remains unchanged. After high temperature heat treatment, the weld seam and the base metal have the same intergranular structure. When performing destructive tests such as flattening, reverse bending, and flaring on the weld, there will be no problems such as cracking, cracking strength, and burrs at the weld. In addition, eddy current testing and water pressure or gas test are also required to ensure the quality of the pipe.
(4) Good consistency - the outer diameter, wall thickness, length and straightness of the pipe are consistent, and the processing precision is high.
