A Study on Some Problems in the Calculations of Corrosion Fatigue Life of Structural Members of an Offshore Platform

ABSTRACT This paper presents the results of research and tests on some problems involved in calculations of corrosion fatigue life of structural members of a platform, using the theory and method of fracture mechanics. According to random vibration theory, the method and a programme for making the random sea wave spectrum and the method for calculating the transfer function of a structural member of a platform are given. The method and programme for composing the spectrum of random stress amplitudes by random sea wave spectrum and transfer function is proposed; finally, for counting the load cycles in estimating the fatigue life, a new method of cycle counting is proposed using two parameters of stress ratio and stress amplitude directly from the random stress spectrum. In order to evaluate the fatigue life, experiments on constant amplitude and random fatigue crack growth rate have been carried out; the Paris' formula has been modified; a programme for the experimental data processing has been given; and the method and an example for calculating residual corrosion fatigue life of the structural member of a platform, based on fatigue damage criteria dadn in terms of the crack growth rate are given, and is illustrated by a sample calculation