Strain ratcheting failure of dented steel submarine pipes under combined internal pressure and asymmetric inelastic cycling

This paper presents the results of an experimental study in which for the first time the progressive inelastic deformation of high strength steel pressurized pipes with plain and gouged dents was analyzed. The effect of some key loading and geometrical parameters such as initial pre-strain (epsilon(mon)) dent depth ratio (delta/D) and the presence of the gouge was studied. Local dents with a hemispherical shape and gouges with different dimensions were introduced on the surface of the specimens. Specimens with plain or gouged dents were first internally pressurized, axially compressed to an initial pre-strain then subjected to cyclic nonlinear stressing. The mechanical defects were found to drastically degrade the inelastic cyclic response of the pressurized steel pipes. The presence of a dent, even with small amounts of initial pre-strains, made the pressurized pipes vulnerable to ratcheting failure. Furthermore, the ratcheting responses of the gouged dented specimens significantly differed from those for the corresponding specimens with plain dents. In fact, the combination of a dent and gouge was the severest form of the defect and demonstrated the lowest number of cycles before failure. The degradation effects of gouge were strongly dependent upon the gouge geometry, dent depth and initial pre-strain level.