Life extension and repair decision-making of ageing offshore platforms based on DHGF method

• This study provides a novel research direction for the life extension and repair decision-making under complicated environments.
• A fuzzy life extension and repair decision-making model was introduced, which provides an exact description of the life process for offshore platforms, as they vary with time.
• DHGF is the combination of practical experience and scientific theory, and is a mathematics method from qualitative and quantitative view.

As platforms age, ensuring their continued integrity becomes increasingly. The current life extension and repair decision-making processes within ageing platforms are typically based on the DHGF algorithm, which was established in order to provide reasonable predictions about the lifespan of ageing platforms, make accurate repair decisions, and reduce risks related to uncertain and complicated environments. The algorithm contains 18 indicators based on the Delphi method, which together-build a complete evaluation system. In this study, the hierarchical structures were established by analyzing and adjusting four dimensions - project factors, risk factors, load factors, and structural factors, and all of them affect the ageing platform service state. The Analytic Hierarchy Process determined a weighted subset. Gray weights were calculated using the gray model theory, and fuzzy mathematics was then applied to form grade evaluation for the ageing platform. A complete evaluation criterion for life extension and repair decision-making was established, and the comprehensive score was calculated by a sequence of computational steps. Analysis showed that the decision making of this platform is ‘Major repair’, fatigue cracks, corrosion, and marine fouling—these factors must be addressed first. The results confirm that the proposed model accurately describes the dynamic, economic lifespan of ageing platforms.