Probabilistic Analyses for Lateral Buckling of Pipe-in-Pipe Systems

Abstract

In order to meet the growing demand for oil production in even deeper waters, new technologies have been developed, making the exploration of such fields possible. A system used as an alternative for the control of extreme operating conditions (high temperatures and pressures) of such exploration fields is the pipe-in-pipe system. This kind of system is extensively used in offshore applications in which exceptional thermal insulation capability is required, preventing hydrate/wax formation and maintaining the production temperature up to the arrival facilities. However, extreme operating conditions can cause the system to experience thermomechanical buckling, which can lead to a structural failure of the system. In order to control these thermomechanical loads and ensure that pipeline is within a safe operating margin, the potential buckling formation locations need to be assessed and may need to be mitigated. The key point in the thermomechanical design of offshore pipelines is to define whether the buckling phenomena should be controlled or not. The optimal solution may often involve addressing natural imperfections whilst establishing the required engineered mitigation measures. Design assumptions such as the pipeline as-laid lateral Out-Of-Straightness (OOS) and the pipe-soil interaction parameters are common input data uncertainties existent during design of HP/HT offshore pipeline systems. A robust design should be impervious to variations in the values of these design parameters, considering values that lie within reasonable and feasible limits, such that the project can proceed with reasonable certainty and within sensible cost limits. In this scenario full of uncertainties, reliability analysis has been implemented in the thermomechanical design of offshore pipeline systems. The purpose of reliability analysis is to reduce the design conservatism by quantifying the probability of failure associated with the pipeline system. This paper presents a novel and viable proposal for conducting probabilistic analysis associated with lateral buckling of a full length pipe-in-pipe system, through the application of detailed finite element analysis. The information contained in the paper can be used as guidance for future reliability evaluations of offshore pipeline systems.