A Generic Methodology for Predicting the Longevity of Offshore Infrastructure

When structures are commissioned, they deteriorate with time. The time to failure of a structure is a function of the mode and rate of overall deterioration of the structure. Considering all the deterioration mechanisms and failure modes possible for detailed analysis is a complicated and inefficient endeavour. Hence, it is useful to streamline efforts by performing Multi Criteria Decision Making (MCDM) analysis (subjective and objective) before performing more detailed analyses. In this paper the methodology for developing a clear path through this process is presented and a case study for deep sea pipelines at cessation of production is presented to highlight the practicability of the methodology presented.
The Multi Criteria Decision Making analysis involves weighing different failure modes against probable risk factors based on expert judgement and existing literature. This is to select the failure mode with the highest risk priority for further objective analyses. The Post-MCDM analysis is performed by the utilisation of representative limit state (performance) functions for determining the response surfaces of the failure modes under consideration and performing reliability analysis based on a streamlined set of deterministic, probabilistic, and stochastic variables.
The results reveal that temperature is a principal stochastic process affecting the deterioration of pipelines when it comes to time dependent analysis. The case study presented demonstrates how effort can be efficiently applied to predict the longevity of offshore structures as well as providing information for key decisions to be made by stakeholders for decommissioning, repurposing, and late life management of offshore infrastructure.