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Difference between Hot Rolled and Cold Rolled Seamless Pipes
May 30, 2022
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1. Different classifications
Hot rolled seamless pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological pipes and other steel pipes.
Cold rolled seamless steel pipes can be classified into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, other steel pipes. It also includes carbon thin wall steel pipes, alloy thin wall steel pipes, stainless thin wall steel pipes and special-shaped steel pipes.
2. Different technological processes
Hot rolled seamless steel pipes: round pipe billet → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → pipe stripping → sizing (or reducing) → cooling → blank pipe → straightening → water pressure test (or defect detection) → marking → storage.
Cold drawn (rolled) seamless steel pipes: round pipe billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → blank pipe → heat treatment → straightening → water pressure test (flaw detection) → marking → storage.
The cold rolling refers to the rolling below the re-crystallization temperature, and the hot rolling refers to the rolling above the re-crystallization temperature.
After hot rolling, the non-metallic inclusions ( mainly sulfides and oxides, as well as silicates) in the steel are pressed into thin sheets, resulting in lamination (inter layer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction and may cause inter-laminar tearing during weld shrinkage. The local strain induced by weld shrinkage is often several times the yield point strain, which is much larger than that caused by load.
3. The diameter of cold rolled seamless steel pipes is often small. The diameter of hot rolled seamless steel pipes is often large.
4. The precision of cold-rolled seamless steel pipes is higher than that of hot-rolled seamless steel pipes, and the price is also higher than that of hot-rolled seamless steel pipes.
Hot rolled seamless pipes
Advantages:
It can destroy the casting structure of steel ingot, refine the grain size of steel, and eliminate the defects of micro-structure, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent. Bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) in the steel are pressed into thin sheets, resulting in the phenomenon of stratification (inter-layer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction and may cause inter-laminar tearing during weld shrinkage. The local strain induced by weld shrinkage is often several times of yield point strain, which is much larger than that caused by load.
2. Residual stress is caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. All kinds of hot rolled steel have this residual stress. The larger the section size of general section steel, the greater the residual stress. Although the residual stress is self-phase equilibrium, it has a certain effect on the performance of steel members under external forces. The deformation, stability, fatigue resistance and other aspects may have adverse effects.
3. For hot-rolled steel products, it is difficult to control the thickness and side width. We are familiar with thermal expansion and cold contraction. Because at the beginning of hot rolling, there will still be a certain negative difference after cooling, even if the length and thickness are standard. The wider the negative difference in edge width, the more obvious the thickness is. Therefore, for the large steel, the steel side width, thickness, length, angle and edge line cannot be required too accurately.
Hot rolled seamless pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological pipes and other steel pipes.
Cold rolled seamless steel pipes can be classified into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, other steel pipes. It also includes carbon thin wall steel pipes, alloy thin wall steel pipes, stainless thin wall steel pipes and special-shaped steel pipes.
2. Different technological processes
Hot rolled seamless steel pipes: round pipe billet → heating → perforation → three-roll cross rolling, continuous rolling or extrusion → pipe stripping → sizing (or reducing) → cooling → blank pipe → straightening → water pressure test (or defect detection) → marking → storage.
Cold drawn (rolled) seamless steel pipes: round pipe billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → multi-pass cold drawing (cold rolling) → blank pipe → heat treatment → straightening → water pressure test (flaw detection) → marking → storage.
The cold rolling refers to the rolling below the re-crystallization temperature, and the hot rolling refers to the rolling above the re-crystallization temperature.
After hot rolling, the non-metallic inclusions ( mainly sulfides and oxides, as well as silicates) in the steel are pressed into thin sheets, resulting in lamination (inter layer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction and may cause inter-laminar tearing during weld shrinkage. The local strain induced by weld shrinkage is often several times the yield point strain, which is much larger than that caused by load.
3. The diameter of cold rolled seamless steel pipes is often small. The diameter of hot rolled seamless steel pipes is often large.
4. The precision of cold-rolled seamless steel pipes is higher than that of hot-rolled seamless steel pipes, and the price is also higher than that of hot-rolled seamless steel pipes.
Hot rolled seamless pipes
Advantages:
It can destroy the casting structure of steel ingot, refine the grain size of steel, and eliminate the defects of micro-structure, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent. Bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) in the steel are pressed into thin sheets, resulting in the phenomenon of stratification (inter-layer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction and may cause inter-laminar tearing during weld shrinkage. The local strain induced by weld shrinkage is often several times of yield point strain, which is much larger than that caused by load.
2. Residual stress is caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. All kinds of hot rolled steel have this residual stress. The larger the section size of general section steel, the greater the residual stress. Although the residual stress is self-phase equilibrium, it has a certain effect on the performance of steel members under external forces. The deformation, stability, fatigue resistance and other aspects may have adverse effects.
3. For hot-rolled steel products, it is difficult to control the thickness and side width. We are familiar with thermal expansion and cold contraction. Because at the beginning of hot rolling, there will still be a certain negative difference after cooling, even if the length and thickness are standard. The wider the negative difference in edge width, the more obvious the thickness is. Therefore, for the large steel, the steel side width, thickness, length, angle and edge line cannot be required too accurately.
