This study presents a lifetime assessment of semi-submersible floating offshore wind turbines (FOWTs) using the Gaidai risk evaluation method. The research focuses on accurately predicting the operational lifespan of FOWTs under various environmental conditions, which is crucial for ensuring structural integrity and safety. The study employs the FAST software package, which integrates aerodynamic, hydrodynamic, and structural models to simulate the dynamic behavior of FOWTs. The Gaidai method is particularly effective for handling high-dimensional systems and is well-suited for evaluating risks in complex, nonlinear environments. The method allows for the simultaneous analysis of multiple dynamic systems' degrees of freedom, which correspond to critical components of the FOWT. The study demonstrates the effectiveness of the Gaidai method in predicting the lifetime distribution of FOWTs by analyzing key components such as the tower's bending moment, blade root bending moment, and anchor tension. The results show that the Gaidai method provides accurate and efficient assessments, enabling better design and operational decisions for FOWTs. The study also highlights the importance of considering extreme environmental loads and the need for robust risk evaluation methods in the design and operation of offshore wind energy systems. The proposed approach offers a novel and reliable method for assessing the lifetime of FOWTs, contributing to the advancement of sustainable energy technologies.This study presents a lifetime assessment of semi-submersible floating offshore wind turbines (FOWTs) using the Gaidai risk evaluation method. The research focuses on accurately predicting the operational lifespan of FOWTs under various environmental conditions, which is crucial for ensuring structural integrity and safety. The study employs the FAST software package, which integrates aerodynamic, hydrodynamic, and structural models to simulate the dynamic behavior of FOWTs. The Gaidai method is particularly effective for handling high-dimensional systems and is well-suited for evaluating risks in complex, nonlinear environments. The method allows for the simultaneous analysis of multiple dynamic systems' degrees of freedom, which correspond to critical components of the FOWT. The study demonstrates the effectiveness of the Gaidai method in predicting the lifetime distribution of FOWTs by analyzing key components such as the tower's bending moment, blade root bending moment, and anchor tension. The results show that the Gaidai method provides accurate and efficient assessments, enabling better design and operational decisions for FOWTs. The study also highlights the importance of considering extreme environmental loads and the need for robust risk evaluation methods in the design and operation of offshore wind energy systems. The proposed approach offers a novel and reliable method for assessing the lifetime of FOWTs, contributing to the advancement of sustainable energy technologies.