Response Surface based Reliability Analysis of Critical Lateral Buckling Force of Subsea Pipelines

Pipeline lateral Out-of-Straightness (OoS) can act as buckle trigger in unburied (exposed) subsea pipelines. Determining the Critical Buckling Force (CBF) of the pipeline is a computationally challenging task due to the inherent uncertainties in contributing parameters which requires utilising reliability-based approaches. This implies the need for a novel framework to develop the response surface (RS) of the CBF of a nominally straight pipeline with rogue lateral OoS which is the subject of this paper and so far, has not been fully explored in the literature. The contributing parameters in CBF are narrowed down through sensitivity studies and the trend of the CBF variation versus OoS curvature and soil lateral mobilisation is established. A novel and structured approach is taken to select the RS sample points. To calculate the CBF of a pipeline with arbitrary design variables, a kriging-based surrogate model is adopted and automated by deploying a Visual Basic Application script. The framework is fully implemented for 6” to 14” pipelines. Monte Carlo simulation is utilised to show some applications of the RS such as reliability of the buckle initiation at engineered buckling sites and susceptibility of lateral buckling considering target reliability limits.