Study On Causes And Risk Assessment Of Internal Corrosion In Weijing Pipeline

Most oil pipelines in China were built early,so the safety operation of pipelines is challenged by the factors such as self-maintenance of pipelines and the change of surrounding environment.Corrosion and perforation often occur.The southern pipeline of Weijing Line has been in operation for more than 40 years,and the phenomenon of internal corrosion,perforation and leakage is becoming more and more serious.It is urgent to find out the main causes of internal corrosion and perforation of the pipeline and work out corresponding solutions.In this paper,on-site sampling was carried out for the pipeline and conveying medium of Weijing Line.The composition,characteristics and surface morphology of the corrosion products were analyzed by SEM,EDS and XRD.X-ray fluorescence and PCR were used in laboratory experiments to analyze the characteristic parameters of the conveying medium and the prediction of scale formation.The sand-carrying capacity of the pipeline under different conditions is studied by numerical simulation.The effects of different factors on the internal corrosion of Weijing pipeline and the corrosion mechanism are studied by weightlessness experiment.Finally,according to the established risk assessment method,the pipeline of Weijing line is evaluated and analyzed,and the control measures are put forward.The main research results are as follows:Through sampling analysis of the unperforated area of the pipeline,pitting corrosion is dominant in the corrosion development area,around the corrosion pit and at the bottom of the corrosion pit.Pitting in the corrosion development area is relatively light,pitting pits are small in size,and the number of pitting pits in the corrosion area is gradually increased and widely distributed,resulting in ulcerative corrosion on the metal surface,with the longest pitting pits up to 0.2 cm.Further XRD analysis of the corrosion products shows that the corrosion products are mainly Fe CO₃ and contain a small amount of Fe₂O₃,which is consistent with EDS analysis data.The results show that the water sample has a serious tendency of calcium carbonate scaling,which is easy to cause underscale corrosion.The comparison of the sand carrying（water）capacity between Yichang oil and Nanyang oil shows that the sand carrying capacity of Yichang oil is weak,which is about 1/3 of that of Nanyang oil.Therefore,sand（water）is more likely to deposit at the bottom of the pipe and form a corrosive environment in the process of backflow meter long oil.The grade of pipeline corrosion damage was evaluated at a total of 612 points in 23locations.Pipelines with different corrosion conditions were classified according to the established risk assessment method,and the fourth and fifth categories of pipe filling or pipe changing were suggested.The residual strength of 561 pipelines with corrosion defects in the second and third categories was evaluated,and corresponding prevention and control measures were put forward according to different situations.