On Longitudinal Propagation of a Ductile Fracture in a Buried Gas Pipeline: Numerical and Experimental Analysis

The work deals with the development of a finite element code, named PICPRO (PIpe Crack PROpagation), for the analysis of ductile fracture propagation in buried gas pipelines. Driving force estimate is given in terms of CTOA and computed during simulations; its value is then compared with the material parameter CTOAc, inferred by small specimen tests, to evaluate the toughness of a given line pipe. Some relevant aspects are considered in the modelling with the aim to simulate the real phenomenon, namely ductile fracture mechanism, gas decompression behaviour and soil backfill constraint. The gas decompression law is calculated outside the finite element code by means of experimental data from full-scale burst tests coupled with classical shock tube solution. The validation is performed on the basis of full-scale propagation experiments, carried out on typical pipeline layouts, and includes verification of global plastic displacements and strains, CTOA values and soil-pipe interaction pressures.