There has been a strong revival of interest in the problem of long propagating ductile shear fractures in gas transmission pipelines. This is related to the development of very high strength linepipe (X100 grade), a requirement to operate at higher pressures and the desire to transmit rich gas mixtures. All of these factors require conditions outside the range of current models for controlling fracture propagation. This paper presents results from a programme of work to enhance the BG energy balance model to include a material strength dependency. It is shown that the previous form of the model is retained but with the kinetic energy term augmented by a plastic work term. The revised model is used to predict crack tip pressure-crack velocity curves. These are combined with a new gas decompression model to predict crack propagation or arrest. Preliminary results from the model are presented.
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