Research On Direct Evaluation Method Of Corrosion In Wet Gas Pipeline Containing CO₂/H₂S In Sand And Sky

With the exploitation of the oil and gas fields,more and more H₂S and CO₂ gases are extracted as associated gas,which are harmful to the pipeline,causing cracking and leakage of the pipeline,resulting in enormous damage of personal and environmental safety.The purpose of this paper is to do internal corrosion direct assessment of Sha-Tian wet gas pipeline,providing theoretical basis for internal inspection and maintenance of pipelines,also,playing a reference role in direct assessment of the same type of internal corrosion.Based on the investigation of the design,operation,maintenance and corrosion data of the Sha-Tian wet gas pipeline,a dynamic indoor high temperature and high pressure reactor experiment was carried out under the typical working conditions of the target pipe.The experimental material was L360,9 series of orthogonal experiments were carried out,the influence of flow rate（1.5m/s,2m/s,2.5m/s）、temperature（35℃,45℃,55℃）and different partial pressure ratio of CO₂ and H₂S（33,50,66,100,150,200,300）are considering in the experiments.Then,using weight lose method to calculate the steel corrosion rate,and microscopic characterization techniques such as SEM,XRD and EDS were used to do corrosion products analysis.The corrosion mechanism of L360 under CO₂ and H₂S co-existence environment were analyzed.In order to have a further study of corrosion behavior of steel under CO₂ and H₂S co-existence environment,a new corrosion prediction model was established based on the mechanism model and experiment results,And the predicted value was verified by the experimental value,the error was controlled within 20%.Combined prediction model with WG-ICDA.DG-ICDA,theory of multiphase flow and multiphase flow simulation technology,setting up a suitable corrosion assessment method to assess the Sha-Tian wet gas pipe,which coiisists of four parts:pre-assessment,indirect inspection,detailed examination and post assessment.Applying the new wet gas pipe internal corrosion direct assessment method to analyze the target pipe.Firstly,collecting the target pipe data to evaluate whether the new method can be used,combining with the relevant specification and operation conditions,then divide subpipe sections.Secondly,using OLGA multiphase simulation software to calculate pipe relevant parameters,analyzing the corrosion of the pipe,and then use the corrosion prediction model to calculate the pipe corrosion and the wall thickness loss,the corrosion-sensitive areas of the pipe were determined by the corrosion rate and the critical inclination angle.Finally,using the existing excavation corrosion rate to verified the corrosion-sensitive areas,and the error were controlled within 20%,which proved that the new assessment method was suitable for the target pipe.Also,the conclusions and suggestions of the internal corrosion evaluation were proposed.At the same time,in order to have a better understanding of the prediction model of steel under COZ and HZS co-existence environment,the BP neural network prediction model and the BP neural network based on genetic algorithm optimization method were established to predict the target pipe,considering the main influence factors of corrosion.Finally,the predicted value were verified by the excavation value,and the error were separately controlled within 20%.