Prediction Of Corrosion Rate And Remaining Life Of Liquid Accumulation In Wet Gas Pipeline With Rough Terrain

At present,the wet gas gathering and transportation process has been widely used,but with the increase of operation time,the accumulation of liquid in the pipeline will aggravate the corrosion of the pipeline,and pose a serious threat to the safe operation of the pipeline and the surrounding atmospheric environment.Therefore,how to make a reasonable prediction of the corrosion of liquid accumulation in the gathering pipeline and make a correct diagnosis of the pipeline corrosion risk area is an urgent need for the safe production of gas fields.Therefore,in view of the internal corrosion problem of the liquid accumulation pipeline in a terrain undulating wet gas pipeline（FZ wet gas transmission trunk line）in Chongqing,this paper analyzes the corrosion law of the fluid operation state,medium and other factors in the wet natural gas gathering and transportation pipeline in combination with the actual situation on site.;Based on the actual operation of the terrain relief wet gas pipeline and the analysis results of the internal corrosion characteristics,the multiphase flow software is used to determine the main sensitive factors of the internal corrosion of the wet and sour natural gas gathering and transportation pipeline and the variation data of various parameters calculated along the line,and the intelligent optimization algorithm is used.A prediction model for the corrosion rate of fluid accumulation in the pipeline under the condition of multi-factor coupling was established;the original sequence of the corrosion depth of fluid accumulation in the pipeline was preprocessed by using the improved grey theory（IGM）,and the error sequence between the actual value and the predicted value was obtained.The optimized BP neural network trains and predicts the error sequence,and establishes the residual life model of the effusion corrosion in the wet gas pipeline based on the improved grey theory（IGM）-AGA-BP.The remaining life prediction system has far-reaching theoretical significance and wide practicability for guiding gas field production authorities to formulate targeted detection methods and safety measures.The main work and results of this research are as follows:1.Based on the analysis of the field detection data of the FZ undulating wet gas gathering trunk line,it is concluded that there are 233 internal metal losses in the wet gas trunk line,and the amount of internal metal loss is relatively concentrated in the range of 0～2km and 4～7km,among which the deepest internal metal loss The loss characteristic is 47%of the wall thickness.The main reason is that the topography of this pipe section is relatively undulating,and it is easy to form acid accumulation at the bottom of the pipe,resulting in accelerated corrosion rate.The corrosion monitoring data in the pipe is analyzed in detail,and the accumulation section of fluid accumulation is determined.For the severe corrosion section,the boundary conditions for simulating corrosion multiphase flow in the topographically undulating wet gas pipeline are also determined.2.Based on the OLGA analysis of the corrosion factors of liquid accumulation in the undulating wet gas pipeline,under different liquid holdup conditions,when the liquid medium liquid holdup along the pipeline is 0.1%～1%and 2%～5%,the wet gas gathering pipeline The corrosion rate increases obviously,and increases with the increase of liquid holdup,but the position of reaching the extreme value of corrosion rate is roughly the same;under different CO₂ partial pressure conditions,the corrosion rate along the pipeline changes obviously,and the overall trend increases with the increase of CO₂ partial pressure;Under different temperature conditions,the corrosion rate of wet gas gathering pipeline increases with the increase of inlet temperature;under different pressure conditions,it has a great influence on the accumulation of liquid,and the corrosion rate changes obviously;under different inclination angle conditions,the upslope inclination angle When the inclination angle is 15°～75°,the corrosion rate decreases with the increase of the upslope inclination angle,and the corrosion rate decreases greatly when the upslope inclination angle reaches 75°.According to the simulation calculation results and field test results,the fluid CO₂ partial pressure,H2S partial pressure,pipeline inclination（ANGLE）,liquid holdup（HOL）,p H value,pressure（PT）,temperature（TM）,overall flow rate（UL）were considered.)Effects of8 corrosion factors on the corrosion rate in wet natural gas gathering and transportation pipelines.3.Based on BP neural network model,grey model GM（1,N）,and genetic algorithm（GA）to optimize the BP neural network method to predict the corrosion rate of fluid accumulation in the undulating wet gas pipeline,the three prediction models can be used to predict the corrosion rate of the undulating wet gas pipeline.The effusion corrosion rate can be effectively predicted,and the prediction trend is roughly the same.The GA-BP model has the best effect,excellent performance and high reliability in predicting the corrosion rate of the pipeline.The results show that the MAPE and RMSE of the GA-BP model are 1.09%and 0.0677,respectively,the prediction effect is very accurate,the correlation coefficient of the predicted value is 0.9965,and the accuracy is 98.91%,reaching the high-precision level,which further proves that the genetic algorithm optimizes the neural network model It is more reliable to predict the corrosion rate of wet gas pipelines.4.Based on IGM（1,1）-AGA-BP,the residual life prediction of fluid corrosion in fluctuating wet gas pipelines,the initial conditions of GM（1,1）were optimized by the time weight sequence,and the IGM-BP error compensation model was combined to establish the IGM-BP model.AGA-BP combination model,and finally use a case to verify the constructed IGM-AGA-BP model.At the same time,the combined model and the IGM model are compared and analyzed to verify the accuracy and reliability of the model,so as to accurately calculate the wet gas pipeline.remaining life.The results show that the maximum relative error of the predicted value of the IGM-AGA-BP model is-4.17%,and the average relative error is 0.48%,which is smaller than the prediction error of GM and IGM,and the prediction error is less than 5%,reaching a high precision level;The test value error RE:GM is 18.04%,IGM is 3.53%,IGM-AGA-BP is-1.66%,much smaller than the other two models,indicating that the established IGM-AGA-BP model has high reliability and good prediction effect.,to meet the engineering requirements;finally,according to the B31G criterion,combined with the prediction model,it is concluded that the pipeline can continue to be used for14.5 years without maintenance in the middle.5.Based on the prediction model of liquid accumulation in the undulating wet gas pipeline,and using MATLAB software to compile the liquid accumulation corrosion prediction system in the wet gas pipeline,the corrosion rate and corrosion depth in the pipeline of the wet gas gathering and transportation system can be predicted and analyzed,and the maintenance and replacement of the pipeline can be carried out.provide assurance.