Theoretical Model for Crack Propagation and Arrest In Pressurized Pipelines

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Abstract:

Need: A mathematical model to simulate crack propagation in a pressurized pipelines.

Result: A theoretical basis for predicting the speed of axial crack propagation and conditions for crack arrest in pipelines was developed and based on a formulation that would be independent of full-scale pipe experiments. This capability would aid in designing pipe experiments and assist in specifying pipeline crack arrest requirements. While exhibiting some degree of success, the model has not been completely adequate for these purposes. The present work was undertaken to fortify some known deficient aspects of the model in order to complete the work.

Benefit: The development of a mathematical model for steady-state crack propagation in a pressurized pipe is described. Recent work was focused on a key parameter in the model--the location of the plastic yield hinge relative to the moving crack tip. This quantity was determined by forcing agreement with crack speeds observed in the full-scale line pipe tests. The maximum crack driving force predicted by the model is taken as a measure of the minimum fracture toughness value required for crack arrest. Comparisons with existing empirical formulations for the minimum required Charpy energy given in this report demonstrates that this approach is quite reasonable. Simple predictive formulas for backfill and non-backfill conditions approximating the exact prediction of the model are supplied for use in line pipe design.

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