Fatigue of threaded tension leg platform tethers

This paper describes the development and implementation of a typical variable amplitude load sequence on tethers for a tension leg platform. The dynamic response of the Hutton TLP was considered in defining a suitable tether tension response spectrum. This spectrum was then used to generate a time series to give a similar amplitude-frequency distribution. Two full scale variable amplitude fatigue tests on large diameter threaded connections are reported using the simulated load sequence. The fatigue test results are compared with constant amplitude results from a previous study on similar connections. A hybrid electric analogue-finite element technique was used to determine the local stress at the critically loaded tooth from which all failures were initiated. Fracture mechanics analysis of the critical cracks was conducted using a recently developed generic weight function solution for threaded connections. Crack aspect ratio was also considered together with previous related studies. In all, the paper presents useful fatigue crack growth data and analysis of threaded tether connections under realistic simulated service loading.