High strength steel line pipes often exhibit anisotropic plasticity and fracture anisotropy due to pipe cold forming. In this study, the plastic behavior of prestrained X100 steel plates was studied showing plastic anisotropy and combination of isotropic and kinematic hardening. Ductility of the steels was also tested along different loading directions using several types of notch tensile bar specimens. Furthermore, numerical simulations of the notched bar tensile tests were performed in order to clarify the prestrain effect on ductility.
As consumption of energy is increasing worldwide, the demand for development of oil and gas resources in remote locations becomes strong. These development areas are often far from major consumers because the potential locations are harsh environments. Environmental loads by offshore ice, discontinuous permafrost and seismic activity impose a strain demand on the pipeline structures transporting the oil and gas from these remote resources to the population centers. While stress-based design of pipeline is normally preferred, the nature of these environmental loads makes strain-based design (SBD) a necessity in these types of harsh environments. Accurate prediction of the environmentally imposed strain by pipeline designers and accommodation of this strain by installation of advanced steels for pipeline is essential to operate a safe and reliable pipeline. The basic materials requirements for line pipe steels is generally control of longitudinal yield strength, low yield to tensile strength (Y/T) ratio, high strain-hardening exponent, high uniform elongation, and good toughness (Glover, 2004). Additionally, aging effects on tensile properties during the coating process must be minimized and fully characterized (Shinohara, 2005; Timms, 2005). For the accurate prediction of strain demand in the new design, we need to consider strain limits at both tensile and compressive side during pipe's bending deformation (Tsuru, 2008; Igi, 2008). In order to determine these strain limits, the full size pipe bending test and the curved wide plate tests are performed.
