Stainless steel has good comprehensive performance and good appearance and surface properties, and is widely used in various industries. Likewise, stainless steel pipes are no exception. Stainless steel pipe is a kind of steel with a hollow section. According to different production processes, it is generally divided into stainless steel seamless pipe and welded pipe. There are also certain differences in their processing methods and properties. The following is a stainless steel pipe manufacturer to introduce to you the difference between the two.
Stainless steel welded pipe:
Stainless steel welded pipe (SS welded pipe) is a pipe made using a welding process. Its manufacturing process is to first bend the steel plate into the required shape, then sew the plates together through welding, and finally form a standard specification pipe through processing and adjustment. Stainless steel welded pipes have the characteristics of smooth appearance, precise dimensions, and smooth surface. They are often used in low-pressure fluid transportation, such as tap water, gas, food processing and other fields.
Stainless steel seamless pipe:
Stainless steel seamless pipe (SS seamless pipe) is a pipe made of perforated stainless steel blanks. Through multiple processing techniques such as cold drawing and cold rolling, the blank is processed into seamless steel pipes. Stainless steel seamless pipes have the advantages of high strength and good reliability, and are widely used in high-pressure and high-temperature applications, such as petrochemical, aerospace, shipbuilding, and nuclear power plant construction.
Stainless Steel Welded Pipe VS. Stainless Steel Seamless Pipe:
1. Different production processes
Stainless steel welded pipe is welded by steel plates or steel strips after being curled and formed by a unit and a mold. There is usually a weld on the inner wall of the pipe.
Stainless steel seamless pipes use round tube blanks as raw materials for perforation, and are made through cold rolling, cold drawing or hot extrusion production processes. There are no welding spots on the pipes. Therefore, seamless pipe manufacturing is more difficult, the production process requirements are higher, and the production cost is relatively high.
2. Different dimensional accuracy
Stainless steel welded pipes have very small wall thickness tolerances and are very uniform throughout the circumference; the steel pipes have high precision, the internal and external surfaces of the pipes are bright, and can be arbitrarily cut to length; thin-walled pipes can be made.
The steel pipe of stainless steel seamless pipe has low precision, uneven wall thickness, low brightness of the inner and outer surfaces of the pipe, high cost of sizing, and pitting and black spots on the inner and outer surfaces that are difficult to remove. Therefore, seamless pipes are usually produced with thicker walls.
3. Different strength and reliability
Because stainless steel seamless pipes are manufactured using a cold working process, they have high strength and reliability, making them safer and more stable to use in high-pressure and high-temperature situations. The strength and reliability of stainless steel welded pipes are reduced to a certain extent due to the existence of welds.
4. Differences in performance and price
Seamless pipes are much better than welded pipes in terms of corrosion resistance and pressure and high temperature resistance. With the improvement of welded pipe manufacturing technology, the mechanical properties and mechanical properties are gradually approaching seamless pipes. The production process of seamless pipes is more complicated, and its price is more expensive than welded pipes.
Stainless steel seamless pipe VS Stainless steel welded pipe: how to choose?
1. Bending resistance
Seamless pipes have higher bending strength than welded pipes and are generally suitable for applications with smaller curvature radius or larger bends.
Welded pipes have poorer bending ability and are mainly suitable for straight pipelines.
2. Pressure resistance performance
Seamless pipes have better pressure resistance because seamless pipes are integrally formed and have no welds, so they have higher pressure resistance. In welded pipes, the weld is a weak link that cannot be extruded, and its pressure resistance is not as good as that of seamless pipes.
3. Cost
The production process of welded pipes is simple, the cost is low, and the price is cheaper than seamless pipes. It is suitable for certain occasions without high requirements.
4. Applicable occasions
Seamless pipes have the characteristics of resistance to stress under high pressure, high temperature and freezing conditions, large flow rate, and good transport fluid performance. They are suitable for pipelines in high-end chemical, chemical, petroleum and other industries, as well as occasions with high wear resistance, corrosion resistance, and high appearance requirements.
Welded pipes are suitable for pipes with low requirements, low pressure and small flow. They are also widely used in some ordinary construction, machinery, bicycles, automobiles, motorcycles and other fields.
Applications of stainless steel pipes:
Based on the characteristics and differences between stainless steel seamless pipes and welded pipes, reasonable selection should be made during application to achieve economical, beautiful and reliable effects:
1. When making decorative pipes, product pipes, and prop pipes, good surface effects are generally required, and stainless steel welded pipes are usually used;
2. For low-pressure fluid transportation in general, such as water, oil, gas, air, heating hot water or steam and other low-pressure systems, stainless steel welded pipes are usually used;
3. For pipelines used to transport fluids in industrial projects and large-scale equipment, as well as pipelines for transporting fluids in power stations and nuclear power plant boilers that require resistance to high temperature, high pressure, and high strength, stainless steel seamless pipes should be selected;
4. Stainless steel welded pipes are generally used for liquid transportation below 0.8MPa, while seamless pipes can be used to withstand liquid transportation above 0.8MPa. If the pressure requirements are not high, it will be more economical to use welded pipes.
Advantages of stainless steel welded pipe
Stainless steel welded steel pipe - stainless steel strips with uniform wall thickness are welded and rolled in one go under gas protection without adding solder.
Advantage:
1. Uniform wall thickness - the base material is formed strip, with good wall thickness consistency and high surface finish, reaching industrial grade 2B.
2. Low residual stress - the formed steel pipe is bright annealed at a high temperature higher than 1040℃ to eliminate stress.
3. High strength of the weld - welding adopts fusion welding and the material composition remains unchanged. After high-temperature heat treatment, the weld and the base material have the same intergranular structure. The weld is subjected to damage experiments such as flattening, reverse bending, and flaring. There will be no cracks, cracks, burrs or other problems at the weld. In addition, eddy current testing and water pressure or gas-gas testing are also required to ensure the quality of the pipes.
4. Good consistency - the outer diameter, wall thickness, length and straightness of the pipe have good consistency and high processing accuracy.
Advantages and disadvantages of stainless steel seamless pipes:
Advantage:
The forming speed is fast and the output is high, and it can be made into a variety of cross-section forms to adapt to the needs of use conditions; cold rolling can cause large plastic deformation of steel, thereby increasing the yield point of the steel. Hot rolling can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate defects in the microstructure, thereby making the steel structure dense and improving the mechanical properties.
Disadvantages:
1. Metal delamination - When steel pipes are cold rolled, non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are pressed into thin sheets, resulting in delamination (interlayering). Delamination greatly deteriorates the mechanical properties of the steel along the thickness direction, and may cause interlaminar tearing when the weld expands.
2. Uneven wall thickness - We all know that metal expands with heat and contracts with cold. Even if the cold-rolled steel pipe reaches the standard in length and thickness at the end of rolling, there will still be a certain negative difference after final cooling. This The larger the negative difference, the worse the wall thickness uniformity. Therefore, the wall thickness, length, straightness and ovality of cold-rolled seamless steel pipes cannot be too accurate.
3. Residual stress - due to uneven cooling, steel pipes of various cross-sections have residual stress. The larger the cross-section size of the steel, the greater the residual stress, which will have a certain impact on performance under the action of external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.
4. Poor surface finish - the stretch marks on the inner surface of the steel pipe are distributed longitudinally, showing symmetrical or single linear folds, some of which exist throughout the entire length, and some of which exist partially.
Due to the complexity of the production process, seamless pipes have poor wall thickness uniformity and poor inner and outer wall surface roughness. In actual operation, it is easy for chloride ion (or sulfide ion) substances (such as organic matter) to bond to the stainless steel pipe wall. , forming a local hypoxic acidic environment, causing the inner wall passivation film to dissolve and lose its protective effect on the metal. The metal directly contacts the medium in the acidic environment, loses electrons as an anode and forms hydroxide with water, and the hydrogen in the hydroxide Oxygen radicals are replaced by chlorine radicals and dissolved in water, reducing the anode passivation effect. The adhesive acts as a cathode to capture the hydrogen ions generated on the inner wall to form hydrogen gas, and discharges them outward together with the reaction products of the metal on the inner wall. As the reaction progresses, the metal on the pipe wall is continuously corroded away to form pitting corrosion, and the holes will gradually deepen and increase.When the temperature rises above 50℃, pitting corrosion accelerates. The higher the temperature, the faster the pitting corrosion rate. Under conditions of large stress, stress corrosion will also occur and show stress corrosion expansion characteristics. In addition, seamless pipes will produce various unstable factors during the welding process, making it difficult to weld firmly and without penetration.
Conclusion:
By comparing the characteristics, advantages and disadvantages, and applicable occasions of stainless steel welded pipes and seamless pipes, it can be seen that stainless steel welded pipes and seamless pipes each have their own advantages and disadvantages, and their applicable occasions are also different. The choice of welded pipe or seamless pipe should be based on specific usage requirements.
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