Fatigue of buried dented pipeline specimens

Abstract

This paper reports the results of fatigue tests performed on dented steel pipeline specimens that were buried and subjected to cyclic internal pressure. Hot-spot cyclic strain amplitudes were measured using two experimental techniques: Digital Image Correlation (DIC) and Fiber Optic Bragg Strain Gages (FBSG). First, full-field measurements were taken using DIC identified strain concentration sites that were potential locations or hot-spots for fatigue cracks to initiate. Close to these point-locations, measurements of strains using FBSG were also taken, and the results were then compared with the DIC results. These fiber gages were also used during the cyclic pressure loading process while the specimens were buried, in such a way as to monitor any possible influence that might be caused by soil coverture restricting the free deformation occurring in the dented areas. These cyclic strain values were used to demonstrate that a simple uniaxial Coffin-Manson fatigue equation that uses the universal exponents proposed by Manson and the circumferential strain amplitude can be used to predict the life of the dented specimens. Moreover, it was determined that the measured strains at the hot-spot locations were not influenced by the soil coverture.