A theoretical model for roller-shape design of three-roller continuous and synchronous calibration process of ovality and straightness for large thin-walled pipes

Large thin-walled pipes are particularly suitable for oil and gas transport and auxiliary pipes in cold areas or deep sea-beds. At present, the rounding and straightening processes are completed independently, and the theoretical model for roller-shape design is analyzed only in a single direction. To solve this problem, a theoretical model for roller-shape design of three-roller continuous and synchronous adjusting straightness and ovality process for large thin-walled pipes is established. The established model is verified by numerical simulation and experimental research using 304 stainless steel pipes. The results show that the three roller-shape design schemes, including three-section, four-section and five-section, proposed based on the theoretical model, can obtain qualified formed pipes. Based on the model, the residual ovality, residual straightness and maximum residual stress of the three roller-shape schemes are discussed. The residual straightness can reach within 0.2%, and the residual ovality can reach within 1%. It verifies the applicability of the model and the feasibility of the process. The model can provide a theoretical basis for presetting the process parameters and optimizing the roller-shape.