A numerical method for predicting O-forming gap in UOE pipe manufacturing

• A numerical method for predicting O-forming gap in UOE manufacturing is presented.
• The formation mechanism of O-forming gap is unveiled.
• The influence of processing parameters on O-forming gap is studied.
• UOE parameter design can be carried out efficiently based on the proposed method.
• O-forming gap can be well controlled by the optimization of UOE parameter design.

Large diameter welded pipes used in oil and gas pipelines are primarily manufactured by the UOE process, which consists of U-forming, O-forming, and expansion procedures. The formation of O-forming gap in the O-forming stage is a key processing factor and it involves complex plastic deformation and springback of the steel plate. In this paper, a numerical method is proposed for predicting geometric configuration and O-forming gap of steel plate after C–U–O-forming. A combined hardening model for characterizing the loading–unloading–reverse loading deformation of pipe steels is developed based on the Chaboche hardening model. The yield plateau phenomenon and the variation of elastic modulus with the increase of pre-strain are incorporated. Industrial experiments are carried out, and the proposed method is validated through comparison between experimental and calculated results. Furthermore, the influence of material and processing parameters on O-forming gap is numerically investigated. The results reveal that U-forming radius is the most important factor in C- and U-forming stages to determine O-forming gap, and the opening gap width increases with increasing of compression ratio in O-forming stage. Finally, the established numerical method is combined with a genetic algorithm and applied to optimize UOE process parameters for obtaining an ideal opening gap. The proposed method provides an effective and efficient tool for UOE process design.