Vahedi, Sayeh; (2004) Modelling the effects of inclination and pipe enlargement on outflow following pipeline rupture. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes the development and testing of a numerical simulation based on the Method of Characteristics for predicting release rates following full bore rupture (FBR) of inclined or enlarged pipelines containing pressurised two-phase hydrocarbons. Two types of failure scenarios involving FBR of inclined pipelines are simulated. These include top end (low pressure) and bottom end (high pressure) rupture. It is found that in the case of top end rupture of the inclined pipeline, the resulting pressure wave propagation and consequently the discharge rate is decelerated compared to a horizontal pipeline. The converse is observed in the case of bottom end rupture. In the case of condensable gases undergoing a phase change during depressurisation, the effect of inclination is not linear, resulting in a dramatic decrease in the discharge rate as the angle of inclination exceeds 20°. However, when the fluid remains in the gaseous state, the effect of inclination is negligible and the gravity term in the formulation of the conservation equations may be effectively ignored. The results of application of the model to the hypothetical rupture of an enlarged pipeline undergoing a rapid change in its diameter reveal that "bottlenecking" results in a significant reduction in the release and hence the depressurisation rates following rupture. Once again, this effect is much more dramatic in the case of two-phase or liquid inventories as compared to those remaining in the gaseous state. This finding highlights the potential of using bottlenecking as an effective means of reducing the failure hazard associated with the accidental rupture of pressurised pipelines. The effects of key parameters such as linear or curved characteristics, the size of the numerical discretisation time step and friction factor on the model's prediction are also examined. It has been observed that the simulation results obtained by applying linear characteristics are in better agreement with published experimental data compared to those based on curved characteristics. In addition, the computational run time for linear characteristics is significantly lower than that for curved characteristics. Investigations relating to the effect of friction factor reveal that during highly transients flows (Re > 7000) such as those encountered during FBR, outflow is relatively independent of the friction factor correlation employed.

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