Reducing diameter variability when expanding large-diameter pipes

The object of the study in this paper is the technology of producing large-diameter electric-welded pipes using the step-forming method, implemented in a production environment at one of the enterprises of PAO TMK. The aim of the work is to investigate the process of step-expanding with a cylindrical tool for the formation of cyclical diameter variations along the length of the pipe blank. The objective of the study is to develop methods and approaches to minimize the formation of cyclic diameter variations along the length of the expanded blank and thereby achieve im-proved quality of the finished product. As part of the work, an analysis of the large-diameter pipe expansion technology was carried out and the causes of cyclic diameter variations were determined. The most critical product ranges suscepti-ble to the formation of this deviation were identified. Simulation models of the pipe expansion process for the selected sizes, as well as accompanying CAD models, were developed. A FEM of the expansion process for the selected pipe sizes was conducted. An assessment was made of the convergence of FEM results with actual inspection results ob-tained using an automated pipe geometry measurement system. Dependencies influencing the magnitude of diameter deviations and cyclical variations in diameter were identified. Modeling the expansion process revealed a cyclical pattern in diameter changes, as well as the causes of these deviations. A method for reducing diameter deviations was developed: introducing a skip zone for expanding with a cylindrical tool (hereinafter referred to as a skip zone) into the process. A relationship was obtained between the skip zone value and the magnitude of pipe diameter variation. The study demonstrated a reduction in diameter deviations by 18–56 %, depending on the pipe size.