The Effect of Tool Joint Stiffness on Drill Pipe Fatigue in Riser Ball Joints

It is well known that the ball joint in a marine riser can cause fatigue damage in the drill pipe passing through. 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 paper extends that work to deep water operations in which an upper ball joint is also present. Also, it is shown, via finite element models, that tool joint bending stiffness can have 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.