What are the defect characteristics of seamless steel pipe?
Seamless steel pipe, as an indispensable material in the modern industrial field, its quality and performance have a crucial impact on the safety and stability of all kinds of engineering projects. However, in the process of production and use of seamless steel pipes, there are often various defects, which not only affect the performance of steel pipes, but also may pose a threat to the safety of engineering projects. Therefore, understanding the defect characteristics and causes of seamless steel pipes is of great significance for improving the quality and use effect of seamless steel pipes.
1. Cracks (cracks)
Cracks are one of the most common defects of seamless steel pipes, and their manifestations are linear or spiral cracks on the inner and outer surfaces of steel pipes. The ends and bottoms of the fractures are often angular and may be netted. There are many reasons for cracks, including poor steel quality, improper heating of tube billet, excessive deformation pressure and so on.
2. Hair lines
The hairline is a continuous or discontinuous hairline on the outer surface of the seamless steel pipe, mostly spiral, and the spiral direction is opposite to the direction of the piercing machine. The causes of hair lines are similar to cracks, which are mainly related to poor steel quality and incomplete cleaning of the blank surface.
3. Infold (infold)
Internal folding refers to the linear or spiral zigzag defects on the inner surface of the steel pipe. For high alloy steel pipes, this defect may appear irregular blocky, distributed at the inlet. The main causes of folding include too much front pressing of the head, serious wear of the head and strong alternating stress on the metal in the center of the blank during perforation.
4. Fold outside
The outer folding is manifested as the spiral folding on the outer surface of the seamless steel pipe, whose spiral direction is opposite to that of the pipe on the punch. The causes of external folding mainly include residual cracks or defects on the surface of the tube billet, poor steel quality and so on.
5. Rolling fold
Rolling folding is a regular folding defect on the outer surface of seamless steel pipe, which is mainly caused by the damage of the roll of the piercing machine or the roll of the tube rolling machine.
6. Fold
The folding is the zigzag caused by metal entering the roll gap or the tube losing its stability in the rolling process, and the local bulge and receding wrinkle on the surface of the steel tube after sizing. The main reasons include that the outlet pipe diameter of the whole machine is more than fixed, the pass shape of the reducing machine, the adjustment is not correct, and the roll dislocation.
