Risk-based structural integrity management for offshore jacket platforms

Abstract

This paper presents a method for risk assessment and inspection plan development as part of the risk-based structural integrity management of offshore jacket platforms. The method provides a global risk assessment for the whole platform's structure and local risk assessment for the platform's structural components (e.g. tubular joints). The global risk assessment uses semi-quantitative or quantitative approaches depending on the available platform's data. The semi-quantitative method is used either at a high level to perform relative risk ranking of platforms in a fleet in order to identify the platforms most at risk and which require more inspection focus or a detailed risk analysis; or at the unit level to define inspection interval and general inspection requirements. The quantitative method involves either structural analysis results (e.g. reserve strength ratio) with a dedicated metocean hazard curve or structural reliability method; and it is used at the unit level only to define inspection interval and inspection requirements. The local risk assessment uses also semi-quantitative or quantitative approach. The semi-quantitative method is used to provide local risk ranking of the structural components of a platform, which allows, if required, local inspections' scope to be defined. The quantitative method involves a probabilistic fatigue method to define inspection plans for selected tubular joints subjected to fatigue and the failures of which are critical for the overall platform structure. The inspection strategy and program, developed by the method presented in this paper, are focused on the routine underwater inspections and are based on the recommended practice of the American Petroleum Institute for the structural integrity management of fixed offshore platforms. An example of application of the method is set out by showing the results of a project carried out by Bureau Veritas.