A Basic Study on Life Assessment of Ships and Offshore Structures

In order to extend lives of ageing ships, it is necessary to make a study on feasibility for extending their planned life. Such feasibility study consists of life assessment with condition survey/assessment, life prediction technique and availability assessment. Nippon Kaiji Kyokai (NK: a classification society) has made a basic study for developing a life assessment system of ships and offshore structures. The logic of procedures for the life assessment is shown diagrammatically in the paper. Hull integrities for life extension having conventional structures will be examined by an empirical method if the structures are well protected from corrosions. However, hull structures with the greater use of high tensile steels have no experience used for a long life exceeding 15 to 20 years as they are of a new generation. Therefore, on a life extension for such a ship, special attention shall be paid to the fatigue strength as well as protection of corrosions. In the paper, studies on fatigue strength for hull structure with mild and high tensile steels and maintenance procedures for good protection of corrosion are briefly reviewed. And some discussions are made to procedures and analytical techniques of an assessment for life extension of ageing ships.