Influence of preliminary deformation on micromechanisms of failure of offshore gas pipeline material

摘要

The S and J - methods of pipe laying tend to increase the brittle fracture component in the material, however, they have practically no effect on the residual life-time of metal under low amplitude cyclic loading (260 MPa). An increase in the stress range up to 320 MPa enhances the negative effect of preloading, which is more pronounced in case of using the S - method of pipe laying as compared to the J - one. Within the high amplitude range (420 MPa) the process of preliminary deformation causes the activation of relaxation processes and longitudinal splitting in the material, giving rise to an abnormal increase in the cyclic life of the plastically deformed material.