Fatigue Analysis of Offshore Structures in Indian Western Offshore
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Oil and Natural Gas Corporation (ONGC), the national oil company of India, operates more than 270 steel tubular welded offshore structures which are piled to ocean bottom. All these structures have been designed to meet the strength and fatigue limit state requirements as per API RP 2A WSD. These offshore structures are subjected to continuous cyclic wave loads and hence fatigue susceptibility needs to be explored. In this paper, stochastic fatigue assessments of an existing offshore platform for life extension purpose have been discussed. The fatigue lives have been estimated as per parametric equations suggested by Efthymiou. A fatigue factor of safety value of 2.0 has been considered in this study, and S-N curves provided in API are used for cumulative damage (Palmgren Miner’s Rule) assessment. All the joints which are found to have lower fatigue lives than design life have been included for type III inspection (as per API RP 2A-WSD) using state-of-the-art NDE techniques (NDT). These studies employed for drawing up the joint inspection campaigns.
KeywordsWelded tubular joints S-N curves NDT Inspection campaign API RP2A Stochastic fatigue
We acknowledge the support and resources provided by ONGC required for carrying out this study. The study has been immensely beneficial in understanding the pertinent issues relevant to the structural behavior of jacket structures and is of vital importance in purview of ONGC’s operational requirements to carry out life extension studies of existing platforms. We extend our sincere thanks to Shri C. Tandi, ED-HoI, IEOT-ONGC for his generous support and encouragement. We are also immensely grateful for the continuous motivation received from Shri Dinesh Kumar, GGM–Head of Structures Section, IEOT-ONGC.
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