Numerical Model for Unstable Ductile Crack Propagation/Arrest in Natural Gas Pipelines Incorporating Soil Backfill Effect

Abstract

Prevention of unstable ductile crack propagation is one of crucial issues in pipeline industry. Some numerical methods for predicting unstable ductile crack propagation/arrest have been developed, of which the Battelle Two-Curve Method (TCM) and the HLP method have been most widely used. Although these two methods are simple and useful, they contain empirical parameters based on the data of full-scale pipe burst tests. Therefore, their applicable range might be limited; their prediction accuracy reportedly drops when applied to the burst tests using new grade pipes and CO2 pipeline burst tests. To overcome their shortcomings, the authors developed a new model, hereafter called “UT model”, without empirical parameters. The UT model describes pipe deformation and gas decompression by one-dimensional partial differential equations, and judges crack propagation/arrest using dynamic energy balance. In addition, the UT model is fully-coupled model which means that the interaction among pipe deformation, gas decompression and crack propagation is considered. Also, soil backfill effect, which constrains pipe deformation, is incorporated into the UT model; kinetic energy of soil surrounding a pipe is dealt as added density of a pipe. In the present paper, the UT model is described in detail, and applied to natural gas pipe burst tests both with and without soil backfill.