Lifetime extension of ageing offshore structures by global ultimate strength assessment (GUSA)

Abstract

Malaysia is the second largest oil and gas producer in Southeast Asia. Majority of jacket platforms in Malaysia have exceeded their design life with various types of underwater structure irregularities. Therefore, it is essential to address the reliability of the jacket platforms in Malaysia due to ageing, increasing environmental loading and demand to prolong the production for a further 25 years. The main purpose of this analyses is to determine the structure’s risk level over its remaining service life which is a vital information in managing ageing facilities to cater for the demand of continuous production. Global Ultimate Strength Assessment (GUSA) methodology was used to support detailed reassessment applied in managing safety, integrity analyses and reliability by evaluating the existing platform’s loading. It is a tool for high-end analysis of structures for Risk-based Assessment (RBA). In this paper, the reassessment of an ageing platform over 30-year-old, still in production is presented to demonstrate GUSA capability to perform the platform’s life extension evaluation. The outcome from these analyses can effectively assist in understanding the structure platform’s failure mechanism and correctly identify mitigation actions required. As part of the analyses, non-linear analysis and probabilistic model as practiced in the industry were used in order to get Reserve Strength Ratio (RSR) and Annual Probability of Failure (POF) results. The accuracy and comprehensiveness of this method will assist the industry, especially oil and gas fields’ operators, in decision-making, specifically in identifying problem-oriented-solutions as part of their business risk management in managing ageing facilities.