Study of Multisource Leakage Diffusion and Explosion Risk of Underground Natural Gas Pipelines

Buried natural gas pipeline leakage is hidden and persistent, and easily can cause environmental pollution, property loss, and casualties, especially in cities. The main objective of this study was to establish a three-dimensional numerical model to restore the real environmental conditions. Taking the small-hole leakage of a buried medium-pressure natural gas pipeline as the accident scenario, the change law of the pressure, flow rate, and velocity of the pipeline and the leakage hole after the occurrence of single-hole and double-hole leakage was studied using the computational fluid dynamics method. The variation rule of natural gas concentration in the soil environment was analyzed, the warning area and hazardous area were delimited, and then the explosion hazard radius of the leaking gas was calculated using the trinitrotoluene (TNT) equivalent method. The results showed that the natural gas leakage diffusion in front of the orifice is similar to a jet phenomenon, and the pressure and velocity gradient decrease sharply with the increase of distance. The mass flow rate and flow velocity of single-hole and double-hole leakage fluctuated within 0–0.4 s after the leakage. The mass flow rate of single-hole leakage was greater than that of the double-hole’s single leakage source, but the mass flow rate of double-hole leakage was 1.98 times that of single-hole leakage. Regardless of the leakage, the orifice velocity and pressure of single-hole and double-hole leakage can reach a stable state after 2 s of leakage, and remained the same. At the same buried depth, it took twice as long for the early warning area and hazardous area to reach the surface with single-hole leakage than with double-hole leakage. The explosion hazard radius of both single-hole and double-hole leakage increased with the increase of pressure, and the explosion hazard radius of double-hole leakage was 1.3 times that of single-hole leakage.