The buckling of externally pressurised pipes degraded by interior corrosion

The research presented in this paper investigated the buckling resistance of initially circular pipes that have suffered interior corrosion. The finite element method is used and novel empirical techniques are introduced. Computer models were produced with varying wear depth along the pipe. Both linear and non-linear analyses using ANSYS APDL (ANSYS Parametric Design Language) with solid shell SOLSH190 elements were performed. The buckling pressures for increasing wear depth for three sizes of theoretical models are presented. Laboratory models tested in previous experimental work were investigated. These results compared extremely favourably, giving confidence in the non-linear FEA analysis. All interior corrosion models were analysed using ANSYS Workbench with Solid 186 elements and different element types were used to validate the results. A reduction factor is proposed which accounts for the effects of corrosion, allowing collapse pressures to be predicted using techniques such as the von Mises and the Windenburg and the Trilling method. This is also known as the David Taylor model Basin (DTMB) formula. In addition, an equivalent cylinder is defined and used with design charts to predict buckling. Both empirical methods were shown to predict buckling pressures for various depths of wear with reasonable accuracy.