COMPARISON OF PLASTIC COLLAPSE SOLUTIONS FOR SURFACE BREAKING FLAWS IN STANDARD ASSESSMENT PROCEDURES WITH FEA

摘要

Engineering Critical Assessment (ECA) procedures generally use the Failure Assessment Diagram (FAD) concept for integrity assessment of components containing flaws. An FAD assessment is described by K_r and L_r values, where K_r reflects the toughness of the material while L_r measures the proximity to plastic collapse. Nowadays pipeline girth welds generally have high fracture toughness (K_(mat)) and it can be argued that plastic collapse is the governing failure mode. The definition of plastic collapse can affect the determination of the L_r parameter and should be carefully chosen. In the present work finite element analysis has been carried out to evaluate the collapse load under local collapse and global collapse conditions. These have been compared with the solutions available in the BS7910 and R6 procedures and the differences have been highlighted. The impact of the choice of plastic collapse solution on the crack driving force has been analysed.