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Continuous assessment of aged offshore structures is becoming extremely important to avoid any hazardous consequences throughout their design life. In Malaysian waters where most of the offshore structures are jacket platforms, it was found that many of these structures are currently operating beyond their design life. With continuous corrosion taking place, structural reliability and operation will be affected. Therefore, for the safety evaluation, this study focuses on the reassessment of an existing aged jacket platform in Malaysian waters pertaining to corrosion effect. In this study, pushover analysis was carried out to determine the ultimate strength of the corroded jacket platform by quantifying the reserve strength ratio value. Two different time-dependent corrosion wastage models were used in the present study to simulate the corrosion behaviour at the splash zone of the jacket platform. It was observed that average corrosion condition relatively simulated the calm waters of Malaysia and by applying this corrosion, the jacket platform can withstand the environmental load acting on it. The results developed in the present study will be useful for future study in predicting and modelling corrosion tolerance of jacket platforms in Malaysian waters.

Explorations by oil and gas companies have moved from shallow to deep water to satisfy consumers' changing needs. A circular-shaped cylinder structure placed in deep water is also known spar platform, is normally floated and subjected to severe conditions which cause unpleasant motions and fatigue damage to the structure. Wake oscillator model is considered a semi-empirical model that is most suitable for the evaluation of Vortexinduced Vibrations (VIV) structure features during the design stage. This work focuses on validation of wake oscillator model for VIV with previously semi-empirical method. Wake oscillator and structure oscillator models are coupled based on the Van der Pol Equation. The coupled models were evaluated and analytically validated. The results showed a qualitative and quantitative agreement with previous analytical, at the same maximum peak amplitude response, 0 = 0.22, with 1.2% percentage error . Meanwhile, experimental results from literature only showed a qualitative agreement but not in quantitative agreement. Analytical modelling may offer potential means for investigating VIV features and provide a fundamental analysis by using a cost saving but reliable method. Further works should be done to characterise the VIV and Vortex-induced Motions phenomenon for spar platform.

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