Challenges of life extension for offshore structures and foundations

Abstract

Life extension of ageing offshore platforms is becoming an increasingly substantial challenge economically and technically. Structural integrity is progressively degraded over time through mechanisms that include fatigue, corrosion, vessel collision, weight increase, seabed subsidence and scour. Furthermore, changes in design codes and metocean data interpretation (such as 10,000 years wave) can have significant influence on the ongoing acceptance of an ageing platform. Successful recognition of the risk due to ageing at early stage and adequate provision of structural redundancy in the design process will improve an assets ability to accommodate additional loads and extended use at the late operation stage. However, excessive conservatism in design can lead to unfavourable cost impact and risk exposure, such as requirement for de-manning and extra structural inspections. The value of a systematic approach such as that within API RP 2SIM is discussed. Feasibility of platform life extension increases if the industry can make better use of recent research and development. Examples of this are pile ageing and avoiding excessive conservatism in pile fatigue life predictions. The implementation of robust methodology and systematic process along with the incorporation of newer technology could be used to demonstrate that an asset remains safe for continued operation.