1. the difference in the production process

4. stainless steel seamless pipe advantages and disadvantages

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 great plastic deformation of the steel, thereby increasing the yield point of the steel. Hot rolling can destroy the cast structure of steel ingot, refine the grain of steel, and eliminate the defects of microstructure, so that the steel structure is dense and the mechanical properties are improved.

Disadvantages:

1. Metal layering-When the steel pipe is cold-rolled, the non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the steel are pressed into sheets, and layering (interlayer) occurs. Delamination greatly deteriorates the mechanical properties of the steel along the thickness direction, and there is a possibility of interlayer tearing when the weld expands.

2. Uneven wall thickness-we are familiar with the fact that metals expand with heat and shrink 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. The greater the negative difference, the worse the uniformity of wall thickness. Therefore, the wall thickness, length, straightness and ovality of the cold-rolled seamless steel pipe cannot be required too correctly.

3. Residual stress-due to uneven cooling, steel pipes of various 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. Such as deformation, stability, fatigue resistance and other aspects may have adverse effects.

4. Poor surface finish-the pull marks on the inner surface of the steel pipe are longitudinally distributed, showing symmetrical or single linear folds, some of which exist through length and some of which exist locally.

Conclusion:

Due to the complexity of the production process, poor wall thickness uniformity and poor surface roughness of the inner and outer walls of seamless pipes, it is easy to bond chloride ions (or sulfur ions) (such as organic matter) on the stainless steel pipe wall in actual operation, forming a local anoxic acidic environment, which dissolves the passivation film on the inner wall and loses 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, the hydroxide in the hydroxide is replaced by chloride and dissolved in water, reducing the anode passivation effect. The adhesive acts as a cathode to capture the hydrogen ions produced by the inner wall to form hydrogen, and discharges them outward together with the reaction products of the inner wall metal. With the deepening of the reaction, the metal of the tube wall is continuously corroded to form pitting corrosion, and the holes will gradually deepen and increase. When the temperature rises to more than 50 degrees pitting accelerated, the higher the temperature pitting faster. Stress corrosion also occurs under high stress conditions and exhibits stress corrosion propagation characteristics. In addition, the seamless pipe will produce various unstable factors during the welding process, and it is not easy to weld firmly and cannot be welded through.