ABSTRACT:

In order to evaluate the Safety of offshore fixed platforms in service, the fatigue reliability calculation for structure members is necessary. The paper analyzes the alternating stress due to sea wave and ice force, and provides new pre - processing programs of hot spot stress calculation. Then the paper presents the fatigue life calculations for structure members under low temperature and ice loading and sea wave loading. At last, considering the three random coefficients: stress calculation B, fatigue life experiment K, fatigue damage calculation Δc the Fatigue reliabilities of structure members are calculated.

1. INTRODUCTION

In order to evaluate the safety of offshore fixed platform in service, it is necessary to calculate the fatigue reliability for structure members. Because the offshore fixed platforms in Bohai endure the sea wave force as well as the ice force action in the winter, so both sea wave force and ice force should be considered for the calculation of the fatigue life and reliablilty. The paper analyzes the alternating stress range due to sea wave and ice force, according to the occurrence probability of sea wave hight and ice thickness for various sea states. In order to calculate the stress range at hot spot, University of Petroleum, China has extended the function of SAP5 computer programs for structure analysis based upon finite element method and provided a new pre - processing programs to modify the SAP5 programs. According to the hot spot stress range, based upon the S-N curve of tubular joint of API code, the fatigue analysis of structure members of fixed platform can be carried out. The S-N curves of tubular joint for normal temperature are provided by API code, but lack of such S-N curves for low temperature.

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