Abstract: Expanding and setting round is one of the most important processes for large diameter longitudinal submerged arc welded (LSAW) pipes production. The research of springback rules for pipe’s expanding and setting round is the theoretical foundation for reasonably determining the process parameters. Expanding and setting round process is divided into three steps, namely, setting round, expanding and unloading in sequence. Based on the process characteristics, the step of setting round is considered as elastic pure bending. The step of expanding is divided into three conditions due to the strain of pipe by elastic critical expanding rate and plastic critical expanding rate, which are pure elastic deformation, partial plastic deformation and pure plastic deformation. The curvature radius of any point on cross-section’s center line is given by geometric constraint equations and springback equation. Excellent agreement is found between theoretical and experimental results, which are obtained by physical simulation experiments and large diameter LSAW pipes. The results indicate the process principles of pipe’s expanding and setting round, as well as the effect law of main influencing factors on the roundness after springback, and which has important practical application value.

Key words: Expanding and setting round, Pipe, Springback, Stretch-bending