Because of the natural life of the pipeline and the impact of artificial factors, pipeline leakage accidents occur frequently. It is very important to detect pipeline leaks and determine the leak location to minimize damage and maintain the safe operation of the pipeline. Be aimed at the products pipeline leak, the CFD simulation software was used to simulate changes in the pipeline pressure. Once the pressure changed at the pipe end and beginning, the pipeline leak happened somewhere. Then under the pressure gradient changes of the pipeline end and beginning, the pressure gradient method was used to ultimately determine the leak location of the pipeline. 

The transportation quantity of backward products in batch transportation of products often changed for some reasons, resulting in the changes of feature of mixed oil during batch transportation. To solve this problem, the governing equations of contaminated product were established based on multiphase flow model. Discrete numerical calculation were made with finitevolume method. The results show that the law of mixedoil’s feature variation is different with the quantity of backward products and among different periods. The increase of the transportation quantity of backward products can reduce the mixed volume, and when transportation sequence is different,the influence of changes of transportation quantity on growth rate of the mixed volume is also different.

Due to the complexity of China's long-distance pipeline via regions, parts of the pipeline assume the big gap transportation inevitably. And dip angles and batch transportation both make great influence on mixed oil characteristics. Aiming at the issue, based on VOF multiphase flow model three-dimensional straight tube is the research subject to simulate numerically the dip angles and the batch transportation's influence on mixed oil characteristics respectively. The results show that the mixed oil concentration decreases gradually with the increase of the dip angle under the conditions of light oil first and heavy one trailing, and when the heavy oil is first and the light one is trailing, the concentration of mixed oil increases gradually as the angles increased. And in the case of heavy oil first, the characteristics of mixed oil is impacted greater by the angle.