Collapse characteristics of flexible pipes under external pressure

As offshore oil and gas exploration takes place at greater depths, so more flexible pipes are failing by collapsing. Here, based on finite-element analysis, full and equivalent models of the dry and flooded annulus collapse of flexible pipes are established and compared. The equivalent models that retain the cross-sectional detail of the main resistance metal layer are highly consistent with the full models, thereby validating the equivalent models. The critical load for dry collapse increases with increasing yield strength of the pressure armor layer, but with dry collapse gradually becoming elastic instability. The critical load for flooded annulus collapse is affected strongly by the yield strength of the carcass layer, and the different yield strengths of the pressure armor layer and carcass layer may cause a different mode of flooded annulus collapse. The results indicate that the yield strength of the carcass layer should be emphasized when selecting the metal-layer materials to improve the critical collapse under flooded annulus conditions, while the yield strength of the pressure armor layer should provide the necessary resistance against plastic buckling in dry collapse.