Unbonded flexible pipes are a key technology in subsea production systems.

Procedures for the assessment of dents and imperfections in steel pipeline are well established and incorporated into industry codes; however, equivalent methods for the assessment of flexible pipes have not been developed. Considering the trend towards production in greater depths and the introduction of novel designs, it is valuable to develop more powerful tools to evaluate the consequences of the presence of defects in flexible pipe due to clashing, dropped objects and other operational damage.

In this article, a finite element model for the assessment of the residual collapse capacity of dented pipes is demonstrated. In distinction to other collapse models, this model allows the complex shape of the carcass layer to be modelled exactly. Based on previous studies and observations of dent types, the indentation process is simulated with different indenter types. The model also incorporates the effects of ovalisation, pipe axial load and static curvature. A parametric model generator and batch job scheduler is included in the model. Validation of the undented model against other assessment methods for flexible pipes is shown. Studies are carried out investigating indenter shape and load and the effects of axial force and pipe curvature on the limit collapse load. Results showing the sensitivity of flexible pipes to dents and imperfections are presented.

This article describes a validated model suitable for assessing damaged flexible pipes under combinations of damage types and loading conditions of use for defect assessment and life extension and provides a tool for developing future guidelines for flexible pipes.

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