The effects of water vapor on the adiabatic flame temperature, premixed flame temperature and laminar premixed flame velocity of methane combustion were studied by using Chemkin 17.0, and the effect of water vapor on the chain reaction process of methane combustion was also studied. The results show that with the increase of water vapor content, the temperature of methane flame and premixed laminar flame speed decrease, and the concentration of H,O,OH free radicals is also reduced, while the proportion of OH free radical is raised, leading to the dominance of reactions transmitted by OH free radicals. The addition of water vapor changes the chain reaction of methane combustion, enhances the reaction of CH3 to CH2(s),CH2(s) to CH2,CH2 to CH,CH to CH2O, and enhances the reaction of CH3 to CH3O,CH3O to CH2O at the same time.

Three⁃dimensional finite element model of buried casing is established using ANSYS software. Through laboratory tests, the relationship between the stress within the center of buried casing and the load on the ground, and the stress distribution in the direction of casing length under different loads is analyzed,respectively. Finally, a three⁃dimensional finite element model is established according to several casing cases in an oilfield. The magnitude of the load on the ground is obtained when the casing reaches the yield strength. The research results can provide a certain reference for the safety protection of pipelines and casing.

Due to the similarity of the routing between HVDC transmission lines and buried pipelines, the local pipelines inevitably enter the HVDC transmission interference zone. In order to study the law of interference and mitigation of HVDC grounding electrode on buried pipeline, boundary element software was used to calculate the effectiveness of various mitigation methods including anti-corrosion coating, the distance between the pipeline and the grounding electrode, insulating joints and zinc ribbon. The results indicated that the smaller the coating breakdown factor was, the more concentrated the interference current was , and the higher the local corrosion risk was. After installing the insulating joints, the strongest interfered section of pipe was alleviated, while the interference of the other section of pipe was aggravated. The protection range of the zinc ribbon was equivalent to the length of the zinc ribbon. Finally, the paper put forward the comprehensive protection measures which included insulating joints, cathodic protection and zinc ribbon.