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　　The forming structure of spiral welded pipe is usually designed according to the forming parameters, and the stress state needs to be considered in the forming process. After the strip steel is processed into spiral tube blank, the stress produced by the tube wall is mainly affected by the forming force in the strip steel forming process. According to the plastic deformation theory, when the relative bending radius of strip steel is equal to 100, the plastic deformation will be very obvious.

　　During the bending deformation of strip steel, a large part will be converted into heat energy, which will lead to the temperature rise of spiral welded pipe. Only a small part of work will stay in the metal and form residual stress in the metal. Most of the energy stored in the metal is lattice distortion stress, which is mainly manifested in the deformation hardening of the pipe wall and the increase of the tensile strength of the steel pipe. At the same time, the inner layer metal and ten thousand layer metal are subjected to pressure and tension respectively, which will produce reverse plastic deformation, and then Bauschinger effect, resulting in the decrease of yield strength of strip steel.

　　At the same time, the forming process of spiral welded pipe should be reasonably designed, usually using the elastic recovery control design, which can effectively control the elastic recovery state of pipe blank, so as to ensure that the elastic recovery state of pipe blank meets the design requirements. The main factor affecting the springback state of tube blank is the yield strength of the material.

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