Validation of Predictions of Wire Stress of Flexible Pipe With Damaged Tensile Armor Wires Under Combined Tension and Bending

Abstract

The nonlinear kinematic response of a damaged 2.5” flexible pipe under combined tensile and bending cyclic loads is simulated and compared to experimental results. High fidelity finite element model substructures are constructed for intact and broken outer and inner armor wire configurations and assembled in a nonlinear dynamic substructuring (NDS) framework to efficiently simulate the full-scale test configurations. Overall, 12 analysis configurations involving all intact wires, up to 4 broken outer wires, and 2 and 4 broken inner wires combined with 4 broken outer wires are constructed. Each analysis configuration is first preloaded axially and then subject to multiple cycles of (i) pure tension and (ii) combined tension and bending. For each case, tensile armor wire strains are extracted from the simulations and compared to strain measurements from the test. For all cases, numerical predictions and test measurements agree well accurately capturing the redistribution of strains into the adjacent intact wires which result in stress concentration factors. This comprehensive demonstration of accurate capture of flexible pipe damaged wire kinematics by high fidelity finite element models and nonlinear simulations has direct applications to flexible pipe integrity management and remnant life assessments. Given that the NDS framework allows highly efficient computation, it is now feasible to execute real-time irregular wave local fatigue simulations with finite element models that include damaged wire data from physical inspections to more accurately predict remnant life.