The reason for the long -caliber thick wall steel pipes is multi -faceted, with the elements of materials and the elements of craftsmanship. If the large -caliber thick wall steel pipe itself has poor plasticity or poor annealing, the probability of vertical cracks will be added, but the root cause is that the large -caliber thick wall steel pipes have high remaining stress after cold pulling.

From the concept of cracking mechanics, the cracking of the component is due to the result of the production and expansion of the internal slight cracks. The long -diameter thick wall steel pipe is based on crispy cracking, and its cracking form is open.

Under normal circumstances, the existence of micro -cracks in metal is inevitable, but if the material conditions are the same, whether the cracking will happen depends on the stress of the effect on the component. The stress of the effect on the component can be loaded with the external load, or the remaining stress that exists in itself.

Large -caliber thick wall steel pipes have a high remaining stress after the cold pulse, especially after empty pulling. This stress is adjacent and axial performance as tensile stress on the neighboring and axis of the high -caliber thick wall steel pipe, and its value can reach the maximum value. According to the above -mentioned tension cracking mechanism, we can think that the cutting of the remaining residual stress that exists in the large -caliber thick wall steel pipe exterior has a key effect on the long -caliber thick wall steel pipe crack.