New developments in burst strength predictions for locally corroded pipelines

Existing industry standards for the integrity assessment of corroded pipelines are based on semi-empirical burst capacity formulae that have poor accuracy. To improve upon this, and to provide a better understanding of the phenomena that govern the maximum pressure capacity of corroded pipelines, analytical models based on sound principles of plasticity theory and large strain continuum mechanics are being progressed within Shell. An accurate burst model for pipelines with corrosion over a considerable length has already been developed (and published) and now the focus is on localized corrosion in the form of a patch or pit. The main objective of the work presented is to investigate the possibility of representing a locally corroded region in a pipe as a plane-strain membrane arch. It is shown that for a shallow arch the pressure capacity is governed by a bifurcation/localization instability.