Steel tube as an inside surface of the tube in the process of hot-rolled wear plug fatigue caused by wrinkling of the short and shallow scratches or the inner tube causes the surface roughness, the system in the subsequent pulling process, the existence of the inner wall of the small tube former pits continually shrink, extend, it evolved into the trench and the trench width smaller and smaller, especially after many empty pull process, steel is committed only by stretching and pulling inward outer membrane squeezing action, the effect of the pipe wall without squeezing out, with the flow of metal, the grooves extend also step tapered inner pipe, and finally form a linear longitudinal inevitable defects; within the blank smooth surface, the inner surface of the finished tube is better. In addition, there may be mold steel pull system in the process, the mold damage on the pipe wall, pulling air in subsequent process, these injuries can not be effectively controlled pressure and Hopewell, followed by the formation of the inner wall of the vertical straight line like defects.

Linear defects because the locus of defective points produced in the lattice by the dislocation lie along a line. This line runs along the top of the extra half-plane. The inter-atomic bonds are significantly distorted only in the immediate vicinity of the dislocation line.

Understanding the movement of a dislocation is key to understanding why dislocations allow deformation to occur at much lower stress than in a perfect crystal. Dislocation motion is analogous to movement of a caterpillar. The caterpillar would have to exert a large force to move its entire body at once. Instead it moves the rear portion of its body forward a small amount and creates a hump. The hump then moves forward and eventual moves all of the body forward by a small amount.