After cold expansion, the diameter of pipes and pipes will increase by about one percent. The difference of diameter, roundness and diameter between the two pipes is greatly improved. The straightness of the pipeline has also been greatly improved. The length of the pipe has been shortened. At 0.5%, the wall thickness decreases by about 0.8%. Overall and effective overhaul of the overall function of steel pipes. Improve the geometric accuracy of seamless pipe and pipe end, make the diameter and roundness of pipe and the difference between the two diameters meet the standard requirements, and facilitate field welding. Tension reduction is a continuous rolling process in which the hollow base metal does not have mandrels. On the premise of guaranteeing the welding quality of the main pipe, the process of reducing the tension of the seamless pipe is to heat the seamless pipe to 950 degrees Celsius or higher, and then roll it into various types (24 times) of stretching reducer with the tension reducer. The finished pipes with outer diameter and wall thickness are essentially different from the hot-rolled pipes and seamless pipes produced by this process. After heating in the heating furnace, the metallographic structure and mechanical properties of the welded joints and matrix can be completely identical. Through rolling and automatic control of multiple stretching reducer, the dimensional accuracy of steel pipe is better than that of seamless pipe of the same kind.



The inhomogeneous deformation during the forming and welding process of seamless pipe reduces the residual stress caused by the forming and welding of pipe, improves its distribution and improves the overall mechanical properties of pipe. These changes should be fully considered in the development of seamless steel tube technology. Consideration should be given to the width, length and thickness of the tube sheet and the outer diameter of the tube before expansion, so that the geometric size of the tube after expansion does not meet the final requirements. For different grids, the cold expansion path also has the effect of improving the straightness of seamless pipe, especially for smaller diameter seamless pipe.