Safety of a deep water marine riser under random loads

The safety of a deep water marine riser subjected to high axial and bending stresses was addressed with respect to potential fatigue failure. A three-dimensional non-linear dynamic analysis of a marine riser was carried out for response calculations. The response histories so obtained were employed for the study of the fatigue reliability analysis of the riser under random wave and random wave plus top vessel motion. A fatigue damage estimation of the riser was made using Miner–Palmgren's rule (S–N curve approach). A non-linear limit state function based on the above approach was derived in terms of random variables. The advanced first-order, second-moment method (Afosm) and Monte Carlo simulation technique were employed for reliability estimation. The design point important for probabilistic design is located on the failure surface. The influence of various random variables on overall probability of failure was studied through sensitivity analysis. The effect on riser fatigue reliability of uncertainties in various random variables is highlighted.