Leakage Characteristic Analysis and Hazard Level Classification of Gas Pipelines Considering Layered Soil Backfilling

Abstract

Soil coverage is the essential difference between buried pipelines and above-ground pipelines. The soil environment affects the leakage and diffusion characteristics of gas. In this paper, the impact of various types of soil layering structures on the leakage and diffusion of natural gas in soil was studied by using numerical simulation. The horizontal hazard range (HHR), the vertical hazard range (VHR), and the surface hazard range (SHR) were defined, five levels of natural gas hazards were categorized, and the degree of accidental hazard under 15 conditions was analyzed by using the lower explosion limit of methane (5% vol.) as the hazardous boundary. The results showed that when the first layer of backfilled soil above the pipeline was clay, the other types and arrangement orders of layered soils had less of an effect on the diffusion of gas concentration. The three layers of soil were subject to greater clay resistance, reducing VHR and increasing HHR and SHR. After 3,600 s of leakage, the hazard level for sand, loam-sand, loam-clay-sand, clay-sand-loam, and clay-loam-sand all reached Level V. The research findings of this paper will provide a reference basis for the design of soil backfilling schemes in the construction of buried gas pipeline projects.