RE-ASSESSMENT OF EXISTING OFFSHORE PLATFORM FOR LIFE EXTENSION

Abstract

Majority of offshore steel platforms in Mumbai High Field in Arabian Sea as well as around the world are about to reach their design life. To continue to operate the platforms after their design life, existing offshore platforms requires re-certification. Also change in design criteria, addition of new facility and damages of the structure may lead to a need for assessment. Underwater & topside surveys are carried out to collect sufficient information about the present condition of the structures for their engineering assessment. The method normally used for assessment of existing offshore structures is In-place analysis based on Design level & Ultimate level check. In-place analysis of the jacket structure has been carried out using SAC’s software to evaluate the structural adequacy of the jacket structure in accordance with code API RP2A criteria’s for life extension. In-place analysis is based on working stress and considers only linear analysis for the jacket structure. If platform does not pass design level analysis, advance analysis such as ultimate strength analysis needs to be carried out as per criteria of API-RP-2A to study failure mechanism of the structure and determine Reserve Strength Ratio (RSR). In ultimate strength analysis both material & geometrical nonlinearity is considered & incremental loading is applied to study the behaviour of the structure. This paper intends to provide Re-assessment of existing fixed offshore steel platform and results from the investigation are discussed and conclusions are drawn about the applicability of the proposed framework.