Research On Prediction Of Remaining Life Of Oil Pipeline Containing Corrosion Defects

Petroleum and natural gas industries has developed rapidly in China,and the construction of oil and gas storage and transportation facilities has accelerated.With the increase in operating time of oil pipelines,the probability of perforation,leakage or rupture or even explosion of the pipe wall due to corrosion also increases.Therefore,the evaluation of remaining strength and prediction of remaining life of buried oil pipelines is an important part of pipeline integrity evaluation.Judging whether the pipeline needs maintenance,replacement or decompression operation by calculating the remaining strength,the remaining life prediction of the pipeline is based on the evaluation of the remaining strength,combined with the development degree of corrosion defects to predict the remaining life of the pipeline,and then formulate a reasonable pipeline inspection cycle.The residual strength evaluation of buried oil pipelines with corrosion defects is studied by improving the B31 G criterion and SY/T 6151 evaluation method.The results show that based on the improved B31 G criterion,the residual strength of the pipeline section in the 27 th year is evaluated to be lower than the standard requirements,that is,the pipeline fails.Based on the SY/T 6151 evaluation method,the remaining strength of the pipe section in the 25 th year is lower than the standard requirements.It can be seen from the comparison that the SY/T 6151 evaluation method is relatively conservative,and the improved B31 G criterion is more suitable for the residual strength evaluation of this section of pipeline.The indoor hanging film method was used to simulate the corrosion rate of a buried oil pipeline in a domestic oil field.The corrosion rate obtained through experiments combined with the B31 G criterion calculates the remaining service life of this section of the pipeline,and the microscopic corrosion morphology of the corrosion coupon after corrosion is observed using an electron microscope.The results show that the corrosion of the surface of the test piece gradually increases with the increase of the immersion time,and the corrosion rate of the pipeline continues to increase with the increase of time,and shows a nonlinear function relationship.Under this condition,the remaining life of this section of pipeline is 30.8 years.The conjugate gradient method improved neural network model is used to predict the remaining life of the pipeline.The results show that the prediction results of the remaining life of the pipeline using the BP neural network model and the improved neural network model based on the conjugate gradient method are basically the same as the observed trend.The neural network prediction model improved by the conjugate gradient method has a simpler structure,relatively fewer hidden layers,less relative error,and better fit.By establishing a time series model,a linear time series prediction is made on the important factors that affect the judgment of the remaining strength and remaining life of the pipeline,and the remaining life of a buried oil pipeline in a domestic oilfield is studied in conjunction with the B31 G evaluation method.The results show that the remaining life of the pipeline is predicted to be 27 years based on the time series model,which is the closest to the remaining life calculated based on the corrosion rate.The time series model predicts the remaining life of the pipeline more accurately,which has practical significance in pipeline safety protection.