Finite element analysis on the dropping impact of hilly pipeline pigging

It's topographically complex along China-Myanmar natural gas pipeline in Yunnan and many large relieves are formed, leading to great potential safety hazards in pigging operation. In this paper, the stress concentration and deformation of hilly pipeline caused by the violent dropping impact of pigs were investigated. Then, dropping impact model was established by means of finite element method to analyze the dynamic characteristics when the pipeline was impacted and the force regularities under the effect of internal pressure, pigging velocity and soil property. It is indicated that the relationship curve of impact force vs. time fluctuates in the shape of pulse when a hilly pipeline is impacted by a pig. The internal pipeline pressure has significant effect on the pigging impact load, and the maximum stress of the pipeline increases with the increase of the internal pressure while the pigging velocity has less effect on the impact load. Furthermore, when the soil is in the soft plastic state, the maximum stress and deformation of the pipeline increase significantly and pipe/soil separation occurs. The research results provide the theoretical basis for the safe pigging of hilly pipelines in undulating terrains.