Application of nitrogen-driven-pig oil returning technology in transformation of oil pipeline

When an oil pipeline is leaking or being replaced, it usually takes the technological measures of non-stop opening and blocking or field oil collecting. These measures, however, are disadvantageous in terms of heavy workload and long time consuming due to field loading and unloading of returned oil, high risk due to oil transportation by road, and the existence of special shaped parts (e.g. the opening flange left after hot tapping) in pipelines. In this paper, the pipeline replacement and oil returning technologies were optimized by using nitrogen to drive pigs. Then, applicable pipe conditions, pig selection and running control of the technology were put forward. The nitrogen-driven pig is characterized by low risk, short oil retuning time and good oil returning effect, and it can provide good technological conditions for subsequent hot work. This technology has been successfully applied in the latent danger disposal. It provides a more economical and safer disposal process for transformation of oil pipeline.