Experimental and numerical studies of the failure of steel jumpers under snag loads

• Rupture behavior of a notched steel subsea jumper was predicted by a failure model.
• Simulation results match with full-scale test results with a < 5% error.
• Failure mechanism of a ductile notched pipe was discovered.
• Optimal notch geometry design was determined.

To limit damage to subsea equipment caused by snag loads, breakaway joints allow failure locations to be strategically defined in the subsea system. A stress modified critical strain (SMCS) failure criterion is used to model the rupture behavior of a notched rigid subsea jumper made from API X65 steel. The jumper is evaluated using finite element analysis when subject to snag loads applied in a given direction. The criterion measures the plastic strain up to failure as a function of stress triaxiality. To verify the accuracy of the failure model, a full scale experimental snag load test is implemented and the resulting snag load-displacement curve is compared with the corresponding finite element simulation. The finite element simulation is observed to predict the experimental load-displacement curve very well up through crack initiation and full breakage at the notched section. Finally, the validated failure model is used in an extensive parametric study of the notch geometry, and design guidance is proposed for an optimally balanced design when consideration is given to snag, fatigue, and operational loading.