A Study On The Maintenance Technology Of West To East Gas Pipeline

The pipelines,which connect oil,gas field and users,play an important role in exploitation and development of the oil and gas industrial field.In recent years,with the ongoing improvements of energy structures and the rising demands for energy,the application of long distance pipeline has been greatly promoted.In view of economy,there are increasing demands for pipelines to have large pipe diameters,high delivery pressures and large transport flows.To fulfill these demands,high strength steel,due to its excellent properties,is being widely used in pipeline industry instead of traditional pipeline steel.Nevertheless,the rapid development of pipeline industry can also induce several problems,such as the service safety and life,as well as the increasing probability of forming welding defects in service.In addition,long distance transmission may also encounter oil-stolen orifice,landslides or geological subsidence.These problems have greatly threatened the pipeline integrity.Therefore,appropriate repair plans should be designed and adopted against all kinds of defects.However,there is no pipeline defect maintenance standard nowadays.In this study,for oil-stolen orifice defects,both the cap repair and fill plate repair methods were analyzed by finite element simulation.In addition,the appropriate structure sizes were figured out using cap repair and fill plate repair,which provided theoretical support for the establishment of enterprise standards.The pipeline integrity assessments were conducted on China western pipelines on the condition of natural disasters such as landslides and subsidence.The proper repair suggestions were proposed for those pipelines which could not go through the integrity assessments.According to the conditions of crack defects in straight pipe,a new type of straight pipe coupling patch clamp was designed.The fixture structure was optimized by finite element analysis,which was light-weight and easy to install.Finally,the case of weld defect failure occurred in the second West-East gas pipeline project was evaluated using fracture mechanics evaluation method.By conducting fracture toughness tests,the spatial variation of critical fracture toughness in welded joints was analyzed.After that,the finite element method was used to obtain the stress intensity factor of pipe including cracks in the service loading conditions.The evaluation results showed that the instability extension would not occur in this pipeline.However,fatigue crack extension tended to occur under the cyclic load,which was identical with the actual fracture observations.This method,which is not only easy to apply,but also with high efficiency and accuracy,can be applied in actual pipeline engineering evaluation.