Design method for fatigue damage performance of offshore underwater drilling wellhead
The fatigue analysis of the subsea wellhead is one of the fundamental requirements for the design of subsea wellheads.Fatigue strength calculation involves the initiation and propagation of cracks in areas of stress concentration under the repeated application of fluctuating stresses(or strains)below the material's yield limit,leading to sudden fracture after a certain number of cycles,a process known as fatigue failure.The number of stress cycles a material withstands before fatigue failure is referred to as the fatigue life.In this study,the fatigue load of the dual wellhead suction pile originates from the varying tension,shear,and bending moments at the lower part of the riser's flexible joint.The cyclic load caused by the action of waves and currents on the platform and riser system is transmitted to the lower flexible joint,where the load magnitude is significantly reduced.The transmitted load continues through the lower marine riser package(LMRP),the blowout preventer(BOP),and the wellhead system.This study focuses on the fatigue damage performance design method for subsea wellheads,analyzing the mechanics of the riser,simulating irregular wave loads,calculating structural dynamic responses,and applying fatigue damage calculation methods.The research concludes with a comprehensive understanding of the fatigue behavior of subsea wellhead systems,providing valuable insights for the design and operation of subsea drilling equipment.