An Efficient Analytical Failure Analysis Approach for Multilayered Composite Offshore Production Risers

Abstract

This paper proposes an efficient analytical failure analysis approach for multilayered composite risers used in the offshore oil industry. This approach is based on a layer-by-layer progressive damage model and a homogenization stress analysis method from which the discontinuous stresses through layers can be efficiently calculated. Different failure theories can be easily integrated into the approach to determine failure initiation in layers with different materials. Progressive failure analysis is based on layer-by-layer material degradation schemes, taking into consideration different failure modes such as yielding, fracture, matrix cracking, fiber broken, etc., in layers with different materials. In this approach, progressive failure information involving failed layers and their failure sequences as well as failure modes can be efficiently predicted for multilayered composite risers under given loading conditions. Failure envelopes of composite risers are generated for either initial failure or ultimate failure in different load spaces, and strengths of composite risers can be predicted under given load ratios. This analytical approach is efficient for failure analysis or strength prediction of composite risers with many layers because stress redistributions in all layers during failure progression can be easily and quickly calculated. A user-friendly interface based on Excel sheets is used to carry out this analytical failure analysis approach. Failure analyses of a 22-layer composite riser under several typical loading conditions are presented to demonstrate the application of the proposed approach. Initial and ultimate failure envelopes of the composite riser are shown in different force spaces. This failure analysis approach provides an efficient way for design of composite risers in the offshore oil and gas industry.