Study on Fracture Criterion for Carbon Steel Pipes with Local Wall Thinning

To assess the fracture behavior of eroded pipes, finite element analyses were performed on the carbon steel pipes with local wall thinning subjected to monotonic four-point bending without inner pressure. The wall thinning of the pipes simulated the defects caused by erosion/corrosion on the inner side of the pipe. The critical hydrostatic-tensile-stress failure criterion with approximation of the relationship between true stress and true strain by the Ramberg-Osgood equation was developed to estimate the displacement of a crack initiation in a pipe at a point where wall thinning is maximum. The developed failure criterion can help estimate fracture ductility under the multi-axial stress condition at the maximum eroded area of a pipe. Screening criterion were calculated by using the developed failure criterion. to classify the fracture behavior of the pipe with wall thinning, as ovalization or crack initiation, on the relationship between the normalized eroded depth, d/t and the normalized eroded angle, 2θ/2π.