It is of great significance to predict the long distance oil pipeline residual life for avoiding leakage accidents and saving repair costs. For the two corrosiondefect points that were dug out on one domestic refined oil pipeline, the threedimensional finite element model of ellipsoidal defect of pipelines structure based on FEA was established. According to the measured dimensions of the two defects of pipeline, the stress analysis of corroded pipelines using nonlinear analysis technique and the remaining life prediction based on plastic limit state failure criterion was also done. The results show that the remaining life of the two corrosion defects were respetively 8 and 13 years. The predicted results could provide theoretical basis for pipeline maintenance and repair.

Gas belongs to flammable and explosive hazardous gas. When the leakage of gas occurred in limited indoor space, the serious consequences would be produced. According to the characteristics of the gas leakage diffusion, firstly Gambit was established indoor gas stove nozzle dispersion physical model. Secondly CFD fluid dynamics software FLUENT was used to simulate the diffusion process of continuous leakage. Finally comparing the diffusion results under certain temperature gradient but different moisture conditions, and monitoring the specified installation area with variety of mounting points, the aim was to optimize the installation position of the alarm. The results show that the location of distance and relative humidity of indoor air were both the key factors on affecting the alarm time. For the same mounting points, relative air humidity increasing 15% would cause delaying the time of alarm nearly 6 s| under the same air relative humidity, each time the alarm was away from the leaking mouth increasing by 1metre, alarm time would lag for 4 s.

According to different damage process of natural gas pipeline leakage diffusion problems, using FLUENT software, CFD simulation model was established, and studied the different leak diameter of the effects on gas leakage diffusion area and simulated the natural gas leak and diffusion process between mountain and city terrain. The situation of wind speed changing along with the height and mass discharge rates variable with the time were taken into account and UDFs were programmed into the FLUENT to amend them. It concluded that the bigger hold can achieve the higher range, the max lower explosive limit of the high from the ground and downwind horizontal distances of diameter of 6.35 , 25.40 mm and 101.60 mm were 92 m and 322 m,122 m and 770 m, 408 m and 1291 m. When diffuses on the surface and in the soil, the 101.60 mm leak diameter had the maximum diffusion range. The biggest downwind horizontal distances were up to 80 m and 105 m respectively. This was because the gas lost a lot of turbulent energy influenced by the soil above the pipeline.

To study the impact of reducer pipeline on batch transportation of mixed product oil when there was a large drop at a crossing point, CFD multiphase flow model was used and transportation control equation was established based on petroldiesel oil mixture. Simulation about mixed volume of reducer pipeline placed in front of or behind the elbow was calculated and presented with pictures. The analysis show that when reducer pipeline placed in front of the elbow, the length of mixed oil was fairly equal and more diesel oil would mix into petrol under the petrol first order. While reducer pipeline placed behind the elbow, the length of mixed oil was longer and the average volume fractions of crossing sections along every axial were unevenly distributed under the petrol first order. Therefore for the reducing of mixed volume, it was appropriate for placing reducer pipeline in front of the elbow and taking the diesel oil first order when batch transportation pipeline was passing through the crossing point.

In regions of complex terrain, refined oil will inevitably pass after elevation, shutdown, such as downhill different path. The pipe inclination angle and shutdown time of downhill pipeline blending have a great influence on mixed oil characteristics. Using CFD multiphase flow model and studying three-dimensional inclined pipe, on the shutdown time, angle and sequence transportation on mixed oil characteristics were numerically simulated respectively. The results of the study show that before shutdown while the forward gasoline and backward diesel, the dip angle is bigger, the mixed oil quantity is less; the inclination angle is smaller, it is more prone to mixed oil. When the forward diesel and backward gas ,contaminated tail is longer and the inclination angle is bigger, the mixed oil quantity is bigger while the inclination angle is smaller, the mixed oil quantity is less but there is less effect on the mixed oil. The inclination angle has greater influence on the former than the latter.After shutdown, the longer the time of shutdown is, the more the mixed oil is with the equal angle. With the same time, the bigger the angle is, the greater the mixed oil. While the forward diesel and backward gasoline, with the shutdown time prolonging the mixed oil quantity is more and more uniform. When the inclination angle and the angle of pipeline is the same, shutdown time and angle has greater influence on the condition of the forward gasoline and the backward diesel.

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.