Study On The Influence Of H₂S And CO₂ On The Internal Corrosion Of The Elbow Of Natural Gas Gathering And Transportation Pipeline In The Flowing State

Along with the extensive development of acidic oil and gas reservoirs,the corrosion of CO2 and H2S in natural gas gathering pipelines has attracted great attention.As the weak link of the pipeline gathering system,the elbow is easy to cause natural gas leakage accidents,which will have a great impact on the safety of the pipeline operation and the surrounding environment.The corrosion process in the elbow is inseparable from the acidic components(gas phase)such as CO2 and H2S and the liquid water(liquid phase),so the flow in the elbow is a typical gas-liquid two-phase flow.At the same time,the natural gas transmission pressure,temperature,flow velocity and flow state change in the elbow interact,and the corrosion problem in the entire elbow is severe and complicated.Therefore,it is necessary to study the influence of C02 and H2S on the internal corrosion of elbows of natural gas gathering pipelines.This paper reviews and summarizes the mechanism,influencing factors and corrosion models of CO2 and H2S corrosion.By comparing the advantages and disadvantages of corrosion rate prediction empirical model,semi-empirical model and mechanism model,according to the actual working conditions,the numerical simulation method is used to study the problem.the DWM model and H2S corrosion rate prediction used in the subsequent simulation are optimized.Empirical model.Through the investigation of the actual situation of the site,the elbow specifications and natural gas parameters and temperament components used in the simulation were selected,and the three-dimensional model of the elbow was established by using 3D CAD software.The structured mesh is divided into three-dimensional model of elbow by ICEM CFD meshing software.Finally,using Fluent software,the VOF gas-liquid two-phase flow model is used to select the pressure-based solver and PISO algorithm for flow field pressure-velocity coupling calculation.The two-phase flow field distribution of the gas flow in the elbow of the natural gas gathering pipeline was calculated,and the CO2 and H2S corrosion models were loaded to simulate the corrosion distribution in the elbow of the natural gas gathering pipeline.The following important conclusions have been obtained through numerical simulation:(1)It is found that the liquid will diffuse to the surrounding area after entering the elbow.The process of liquid phase fragmentation spreading to the surrounding wall is a key factor in the corrosion of the elbow.(2)There is no obvious regularity in the distribution of CO2 and H2S in the elbow.In general,the content of acidic components on the outer side of the elbow is higher than that on the inner side.The above phenomenon may be related to the tangential velocity.The distribution of CO2 and H2S in the elbow is related,and the distribution of CO2 and H2S has a decisive influence on the corrosion characteristics of the inner wall surface of the elbow.(3)With the increase of CO2 concentration in the elbow,the maximum corrosion rate of the elbow wall and the average corrosion rate of the wall surface increase.The increase in CO2 concentration not only increases the local maximum corrosion depth,but also increases the corrosion of the entire wall.(4)With the increase of the inlet flow velocity,the area of the largest corrosion area of the elbow wall(the outer side of the elbow)is obviously enlarged,and the increase of the maximum corrosion rate is significantly larger than the average corrosion rate increment,indicating that the mass transfer rate is increased by the increase of the inlet rate.The process has a greater impact on localized corrosion,while the corrosive effect on the inner wall of the entire elbow takes longer to enhance the diffusion process of CO2.(5)The change of water content(0.002?0.1)not only has little effect on the corrosion rate of the elbow wall,but also has little effect on the corrosion distribution of the inner wall surface of the elbow.In this paper,the distribution of H2S?CO2 corrosion rate of elbow and the influence of concentration,flow rate and water contenton H2S?CO2 corrosion of elbow aresimulated.The conclusion so btained provide are ference for the formulation of corrosion protection and controls chemes fore lbow so natural gas gathering pipelines,and are of great significance for the safe operation of natural gas pipeline systems.