Residual stress of seamless steel pipe during cold drawing

Seamless pipe is a pipe with a hollow cross-section, which is widely used for conveying fluids, such as octg pipes for conveying oil, natural gas, gas, water and certain solid materials. The production of seamless steel pipes requires a cold drawing process, and the additional stress in the cold drawing process results in uneven deformation of the seamless steel pipes, which becomes the residual stress after cold drawing.

The degree of non-uniform deformation of seamless steel pipe determines the size and distribution of residual stress. The cold drawing deformation of seamless steel pipe is determined by its deformation characteristics. Because there is no mandrel in the drawing process, and the thickness of the pipe wall does not change much and then deforms, the deformation conditions are very different from the deformation state of the inner and outer layers of the seamless steel pipe, resulting in uneven deformation. During the deformation process, the metal on the inner surface of the seamless steel pipe first enters the state of plastic deformation, and the metal flows along the axial direction without friction. Therefore, uneven axial deformation occurs along the wall thickness direction, resulting in the natural elongation of the outer layer of the seamless steel pipe being significantly lower than that of the inner layer. In this way, the generation of additional axial and tangential tensile deformation and additional stress reaches the maximum in the outer layer of the seamless steel pipe. On the contrary, the additional compressive deformation and compressive stress of the seamless steel pipe produced in the layer also reaches the maximum value, and the additional stress becomes the residual stress and remains in the pipe after deformation.

Seamless steel pipes are widely used. General purpose seamless steel tubes are rolled from ordinary carbon structural steels, low alloy structural steels or alloy structural steels with the highest yield, and are mainly used as pipes or structural parts for conveying fluids. Compared with solid steel such as round steel, the steel pipe is lighter in weight when the bending and torsional strength is the same, and it is an economical section steel. The production process of seamless steel pipe manufacturers can be divided into two types: cold drawing and hot rolling. The production process of cold drawn seamless tubing is generally more complicated than that of hot rolling. The tube billet is firstly subjected to three-roll continuous rolling, and then the sizing test is carried out after extrusion. If there is no response crack on the surface, the round tube is cut by a cutting machine, and the billet is cut into a billet with a length of about one meter.

In short, the uneven deformation of the seamless steel pipe after drawing leads to a large residual stress of the seamless steel pipe. Therefore, reducing the residual stress drop after cold drawing is an effective way to avoid longitudinal crack damage.

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