Marine risers

A key design challenge for pressure armor layers in flexible risers is the determination of the influence of global riser loading conditions on the local nub-groove fretting conditions. This work presents a combined experimental-computational methodology to develop a fretting design tool for flexible marine risers. Pressure armor material tribological characteristics, such as coefficient of friction and wear coefficient, and fatigue characteristics, are established for relevant local nub-groove loading conditions. Global-local riser analysis is conducted using the Flexcom finite element (global) dynamic analysis software for flexible risers, for the definition of input boundary and local loading conditions for a local finite element frictional contact model of nub-groove contact. These computational tools allow identification of nub-groove contact pressure, tangential stroke or slip, and substrate stresses caused by global environmental loading conditions, such as riser bending moment, axial load, external hydrostatic pressure, and internal fluid pressure. This methodology allows for the experimental characterization of pressure armor material and the development of a global-local dynamic fretting design methodology. This is then implemented in a design case study for a real-life riser application.