Leakage diffusion characteristics and harmful boundary analysis of buried natural gas pipeline under multiple working conditions

Natural gas transportation heavily relies on buried natural gas network. Unfortunately, natural gas pipeline leakage can cause environmental pollution and resource loss, and even leads to serious risks on human's life and properties due to its flammable and explosive properties. In this study, numerical stimulation methodology was applied to investigate the leakage and diffusion characteristics of buried natural gas pipeline, and the first dangerous time (FDT), farthest dangerous range (FDR) and ground dangerous range (GDR) were utilized to track harmful boundary for gas leakage and diffusion. By exploring thirteen different working conditions and evaluating the impacts of six parameters on harmful boundary, prediction models for harmful boundary was successfully established. The results demonstrated that the effect of soil on the pressure and velocity of the leaking hole occurred within 30 s right after pipeline leaked. Sonic flow was absent at the leaking hole, while reversal flow was present at the pipeline downstream of the leaking hole. Soil types play a critical role on harmful boundary: FDT increased by more than five times, FDR decreased by more than two times and FDR remained zero when soil type switched from sand to clay. Larger leakage diameters and higher pipeline pressures can raise FDR and GDR, but reduce FDT. In this prediction models, the average errors for FDT, FDR and GDR were 8.81%, 1.51%and 3.82% respectively. This is the first study to assess harmful boundary by utilizing prediction models. This work will provide reasonable time estimation for emergency evacuation, but also suggest the location setting of underground gas leakage monitoring points.