This thesis describes the fundamental extension, development and testing of audmathematical model for predicting the transient outflow following the failure ofudpressurised pipelines. The above encompasses improvements to the theoretical basis andudnumerical stability, reduction in the computational runtime and the modelling ofudfracture propagation with particular reference to CO2 pipelines.udThe basic model utilises the homogeneous equilibrium model (HEM), where theudconstituent phases in two-phase mixtures are assumed to be in thermodynamic andudmechanical equilibrium. The resultant system of conservation equations are solvedudnumerically using the Method of Characteristics (MOC) coupled with a suitableudEquation of State to account for multi-component hydrocarbon mixtures.udThe first part of the study involves the implementation of the Finite Volume Methodud(FVM) as an alternative to the MOC. In the case of gas and two-phase hydrocarbonudpipeline ruptures, both models are found to be in excellent accord producing goodudagreement with the published field data. As compared to the MOC, the FVM showsudconsiderable promise given its significantly shorter computation runtime and its abilityudto handle non-equilibrium or heterogeneous flows.udThe development, testing and validation of a Dynamic Boundary Fracture Modelud(DBFM) coupling the fluid decompression model with a widely used fracture modeludbased on the Drop Weight Tear Test technique is presented next. The application of theudDBFM to an hypothetical but realistic CO2 pipeline reveals the profound impacts of theudline temperature and types of impurities present in the CO2 stream on the pipeline’sudpropensity to fracture propagation. It is found that the pure CO2 and the postcombustionudpipelines exhibit very similar and highly temperature dependent propensityudto fracture propagation. An increase in the line temperature from 20 – 30 oC results inudthe transition from a relatively short to a long running propagating facture. The situationudbecomes progressively worse in moving from the pre-combustion to the oxy-fuel stream. In the latter case, long running ductile fractures are observed at all theudtemperatures under consideration. All of the above findings are successfully explainedudby examining the fluid depressurisation trajectories during fracture propagation relativeudto the phase equilibrium envelopes.udFinally, two of the main shortcomings associated with previous work in the modellingudof pipeline ruptures are addressed. The first deals with the inability of Oke’s (2004)udsteady state model to handle non-isothermal flow conditions prior to rupture byudaccounting for both heat transfer and friction. The second removes the rupture planeudinstabilities encountered in Atti’s (2006) model when simulating outflow following theudrupture of ultra high pressure pipelines. Excellent agreement between the new nonisothermaludmodel predictions and the published data for real pipelines is observed.
展开▼
