Modelling pipeline decompression during the propagation of a ductile fracture

There is considerable interest world wide amongst major pipeline operators in investigating the potential for using high-strength steels for long distance gas transmission pipelines. Although pipelines that are constructed from such materials will have higher material costs, economic studies' have shown that overall there will be a significant capital expenditure saving on a long (greater than 1000km) transmission Line if such steels are used. However. one problem associated with the introduction of pipelines made from high-strength steels is the ability to demonstrate that a propagating ductile fracture occurring in the pipeline will be arrested. That is, there is a need to show that such fractures, which are highly unlikely to occur in practice, will not propagate beyond a small number of pipe joints. The present paper focuses on one specific aspect of this, namely the prediction of the gas decompression within the pipeline as a ductile fracture propagates along the pipeline. A mathematical model is proposed that relates the pressure in the pipeline to the velocities generated in the pipeline. It is shown that if real gas thermodynamics are taken into account, rather than assuming ideal gas behaviour, then this model is in good agreement with experimental data. It is also noted how this model can be used in practice, both directly in the design of pipelines and to help design experiments to study pipeline fractures.