The reason and treatment plan of the crack of seamless steel pipe

There are many reasons for longitudinal cracking of seamless pipes, both material and process reasons. Taking the thick-walled seamless steel pipe as an example, if the thick-walled seamless steel pipe has poor plasticity or poor annealing, the probability of longitudinal cracking will increase, but the fundamental reason is that the residual stress of the cold-drawn thick-walled seamless steel pipe is large.
  
According to the concept of cracking mechanics, the cracking of components is the result of the formation and propagation of internal micro-cracks. The longitudinal cracks of thick-walled seamless steel pipes are basically brittle cracks, and the cracks are in the form of openings.

In general, the existence of metal microcracks is unavoidable, but under the same material conditions, the generation of cracks depends on the tensile stress of the component. The tensile stress affecting the member can either be loaded outside the member or exist in the residual stress of the member.
 
After cold drawing, especially after air drawing, the residual stress is large, which is manifested as the tangential and axial tensile stress near the outer surface of the thick-walled seamless steel pipe, and its value can reach a large value. According to the above tensile cracking mechanism, it can be concluded that the tangential residual stress near the outer surface of the thick-walled seamless steel pipe plays a key role in the longitudinal cracking of the thick-walled seamless steel pipe.