Stress-life fatigue assessment of pipelines with plain dents

This paper presents a new algorithm for assessing the fatigue life of dented pipelines. The proposed methodology was conceived according to the current stress-life fatigue theory and design practice: it employs S-N curves inferred from tensile test material properties and uses well established methodologies to deal with the stress concentration, the mean stress and the multi-axial stress state that characterizes a dented pipe. Finite element analyses are carried out to model the denting process and to determine the stress concentration factors of several pipe-dent geometries. Using dimensional analysis over the numerical results, a non-dimensional number to characterize the pipe-dent geometry is determined and linear interpolation expressions for the stress concentration factors of dented pipelines are developed. Fatigue tests are conducted with the application of cyclic internal pressure on small-scale dented steel pipe models. In view of the fatigue test results, the more appropriate S-N curve and mean stress criteria are selected.