Experimental and analytical fretting characterisation of pressure armour nub-groove contact in flexible marine risers

•Development of a fretting rig for testing of pressure armour material under representative nub-groove fretting conditions.•Analytical analysis of wear using a computationally-efficient simulation for use in flexible riser design.•Three dimensional analysis of stresses and fatigue damage in fretting rig specimen. This paper presents the development of a test rig for the characterisation of fretting in the nub-groove contacts of pressure armour layers in flexible marine risers and an analytical design tool called EASY-FRET (Engineering Analysis SYstem for FRETting) for fretting wear, fatigue and stress analysis of fretting contacts. The test rig characterisation includes both partial and gross slip fretting regimes under representative three-dimensional crossed-cylinder contact pressure and slip fretting loading conditions, identified from finite element global-local modelling of the complex geometrical-loading configuration. The analytical design tool simulates wear and associated fretting fatigue indicator parameters. The ability to predict the fretting wear and fretting fatigue in flexible marine risers will allow for less conservative design.