To study the diffusing of gas piercing leakage, finite volume method is used to establish CFD simulation model that detects different locations where gas pipes leak and four styles of diffusing, leakage of the upper, lower, windward and leeward side of the pipeline, were numerically simulated. According to the research, the leakage of lower is closer to the ground and diffuses less easily than the upper leakage, which has a 30～70 m larger dangerous area of cross range section. The leakage of windward side is similar to the leeward side, but the lengthwise section area of the former leakage is larger and more dangerous than the latter. And this simulation of leakage area provides theoretical base for safety transportation of gas and security maintenance of pipelines.

Factors that affect pipeline safety and reliability are numerous and randomness, so directly solving the limit state equation is difficult. The solving process of using RF method is simple and high precision. Based on reliability theory and B31G-1991 standard, comprehensively considering the randomness of the corrosion defect length, radial depth of defect, the corrosion rate, wall thickness, pipe yield strength and pressure pipelines, using RF method established a mathematical model for the reliability analysis of corrosion piping. The computer program for this method was developed. The results show that reliability index of the pipe decreased with the increase of defect length, defect depth, and the radial in corrosion rate and that the defect depth is the main factor of pipeline failure. The pipeline reliability index with the pipe yield strength increases in a linear increased, and rapidly reduces with inside pressure increasing.