Forming and Buckling Simulation on High-strength UOE Pipe with Plastic Anisotropy

New guideline is required in forming high strength steel line pipes since springback is quite higher than that of the conventional materials. Moreover, line pipes have plastic anisotropy, which the work hardening coefficients are different between the longitudinal and the circumferential direction, caused by the forming strain and the strain aging during the heating in anti-corrosion coating. However, the effect of the plastic anisotropy on the pipe performance has not been clarified. This paper describes the numerical simulation models of the UOE pipe forming and the pipe bending with two different yield functions, which are capable of representing the plastic hysteresis and the orthogonal anisotropy respectively. The forming models introduce the operating guidelines corresponding to the material strength and the design indexes of the apparatus to aid the lack of the press capacity. The bending models reveal that yield point elongation on stress vs. strain curve in the circumferential direction in addition to the longitudinal direction degrades the buckling resistance and the decreasing rate is dependent on internal pressure.