L52245 Improvements to the Two Curve Ductile Fracture Model - Soil-Elastic and Plastic Contributions

The most commonly used fracture analyses procedure for the prediction of minimum arrest toughness and fracture speed for axially running cracks in line pipe materials for natural gas transmission pipeline applications is the Battelle Two-Curve approach. This analysis procedure incorporates the gas-decompression behavior with the fracture toughness of the pipe material to predict the minimum Charpy energy required for crack arrest. For this model, the effect of backfill on the propagating crack fracture speeds is lumped into one empirically based “backfill coefficient,” which does not distinguish different soil types or strengths. This report provides a better understanding of soil behavior and its affect on the fracture speed of running axial flaws in buried line pipe materials. The results from this program are combined with other full-scale experimental data in developing a modification to the treatment of backfill in the Battelle Two-Curve approach for calculating minimum arrest toughness. This first major improvement to the Battelle Two-Curve approach is incorporated into a computer code called PIPE-DFRAC.