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Description:
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It is well known that the ball joint in marine riser can cause fatigue damage in the drill pipe passing through it . Previous investigators have assessed the damage done for a lower ball joint angle of 3 -5 degrees (drilling ) and 1 -3 degrees (running casing ) . This research extends that work to deepwater operations in which an upper ball joint is also present . Also , it is shown , via finite element models , that tool joint bending stiffness has a significant effect on fatigue life . Fatigue damage calculations including this heretofore unconsidered effect are presented for various ball joint angles and drill pipe tensions . |