Research On Corrosion Mechanism And Countermeasures Of Oil And Gas Gathering And Transportation Pipelines In A Block Of Tahe Oilfield

The oil and gas gathering and transportation pipeline in a certain block of Tahe Oilfield fluctuates greatly along the way,and the flow state of the medium in the pipeline is changeable.The transportation medium contains H₂O,CO₂,H₂S,Cl^-,etc.,and the internal corrosion environment is very complicated,which leads to serious corrosion problems of the gathering and transportation pipeline.At present,L360QS anti-sulfur steel is mainly used for gathering and transportation pipelines in this block.The corrosion problem has not been significantly improved,and the influencing factors and mechanism of corrosion are not clear enough.The expected protective effect has not been achieved through surface engineering and adding corrosion inhibitors.Therefore,it is necessary to study and determine the main influencing factors and mechanism of corrosion of gathering and transportation pipelines.Aiming at the corrosion problem of oil and gas gathering and transportation pipelines in a block of Tahe Oilfield,this paper takes the 53X gathering and transportation pipeline as the research object,uses numerical models and laboratory experiments to simulate the on-site corrosion environment,and explores the flow pattern,medium composition,pressure,hydrogen sulfide The corrosion law of L360QS steel by partial pressure,temperature and flow velocity was determined by linear fitting and comprehensive analysis of grey relational degree.Using SEM,EDS,XRD,SPM and other instruments to analyze the corrosion components and structures on the surface of the corrosion samples,combined with the corrosion product components and corrosion forms,the mechanism of corrosion of oil and gas gathering and transportation pipelines in a block of Tahe Oilfield was determined:CO₂ corrosion was used as the Mainly,H₂S corrosion is supplemented,including chemical reactions at gas-liquid interface,in solution,solution/metal interface;charge transfer at solution/metal interface;mass transfer of corrosive substances in solution.When CO₂ and H₂S gas are dissolved in water,CO₂ will form H₂CO₃ when it meets water,and H₂S will be ionized when it meets water,which reduces the p H of the solution and intensifies the corrosion of carbon steel.Fe CO₃ and Fe S are deposited on the surface of carbon steel substrate to form a product film.Due to the change of local medium flow state,the compactness,thickness and integrity of the product film cannot be compensated.High concentrations of Cl^-will continue to accumulate along the defects of the product film and destroy the product film,thereby promoting local corrosion and increasing the tendency of pitting corrosion.The Ca CO₃ scale layer will also synergistically promote pitting corrosion.The corrosion of L360QS steel is affected by the cathodic reaction process,and the influence of different factors only changes the corrosion rate,but does not change the corrosion mechanism.Based on corrosion influencing factors,action mechanism and field practice,and according to relevant standards and specifications,the field environment is simulated,and two anti-corrosion measures,adding corrosion inhibitor and non-metal lining,are studied.The dynamic corrosion inhibition experiment and electrochemical method were used to optimize the corrosion inhibitor.The results showed that the uniform corrosion inhibition effect and pitting corrosion inhibition effect of the THYT-Ⅱ*type corrosion inhibitor compounded by10mg/L Al Cl₃ solution was better when the concentration was 40mg/L.Good,and more economical,recommended for field use.Through numerical simulation and high temperature and high pressure dynamic corrosion experiments,the non-metallic lining materials are selected.The results show that the PVDF lining pipe with a wall thickness of 8 mm has the smallest impact on the transportation volume of the gathering and transportation pipeline（DN400）,and its net present value is the largest.Under the on-site environmental conditions,PVDF can maintain the original surface microstructure and internal structural components,the heat resistance and pyrolysis behavior are not affected,the temperature resistance is good,and its on-site adaptability is strong.And determined the PVDF lined pipe size required for different sizes of pipes under three pressure conditions of 1.5MPa,3.5MPa and 5.5MPa.On this basis,a four-level control strategy based on pressure,temperature,CO₂ molar content and H₂S content was proposed to optimize the internal corrosion control process of gathering and transportation pipelines.