Collapse of thick deepwater pipelines due to hydrostatic pressure

The collapse-behaviour of pipes was to be studied by use of Finite Element modelling.Existing analytical expressions for collapse were evaluated and especially the one used inDNV-OS-F101 was decided to be studied in comparison with FE-model results.Parameters that may influence the collapse capacity and are not included in the analyticalexpressions –flattening, peaking, eccentricity, local wall thickness variation, materialstress-strain curve, residual stresses - were defined and explained. A model was built inthe Finite Element software package Abaqus v6.9.1 and several articles on collapsetesting used to verify it. The aforementioned parameters were studied by use ofsensitivity studies and the results shown and discussed. Effective thickness definitions foruse in the DNV-formula and the DNV-yield stress criterion were discussed in the contextof the results. The results seemed to indicate that the transition between the elastic andplastic range of the material stress-strain curve was of great importance. The results werediscussed in the context of the different collapse-related parameters defined beforehandand some concluding remarks were made on possible further work related to thesefindings.