Fatigue resistant coupling for tubular members

Abstract From the Canadian patent

An extended life coupling for joining tubular members in an end-to-end relationship is disclosed. The coupling is of simply design having only three components: a pin, a box and a threaded lock ring. An external compressive axial preload places a torus on the pin in axial compression. Make-up of the lock ring maintains the compressive strain on the torus and the lock ring when the axial make-up force is removed. Thereafter increased tensile loading on the pin and box is partially absorbed in benign compressive stress of the locking ring. By controlling the geometry of the coupling such that the stiffness of the torus is high compared to the stiffness of the box and the stiffness of the lock …