Global sensitivity analysis of the impact of impurities on CO₂ pipeline failure

This paper describes the testing, comparison and application of global sensitivity techniques for the study of the impact of the stream impurities on CO₂ pipeline failure. Global sensitivity analysis through non-intrusive generalised polynomial chaos expansion with sparse grids is compared to more common techniques and is found to achieve superior convergence rate to crude Monte Carlo, quasi-Monte Carlo and EFAST for functions with up to a moderate level of roughness. This methodology is then applied to the hypothetical full bore rupture of a 1 km CO₂ pipeline at 150 bara and 283.15 K. The sensitivity of the ensuing outflow to the composition of a quaternary mixture of CO₂ with N₂, CH₄ and O₂ as representative stream impurities. The results indicate that the outflow rate is highly sensitive to the composition during the early stages of depressurisation, where the effect of the impurities on phase equilibria has a significant impact on the outflow.