Corrsion Failure Analysis And Protection Countermeasures Of Heat Exchanger In 800 Thousand Light Hydrocarbon Plant

As an important place for natural gas processing,storage and gathering,the safety of light hydrocarbon plants has attracted much attention.A large number of heat exchangers in the plant area are characterized by high temperature,high pressure,strong corrosion,high flow rate,etc.,often causing corrosion leakage and flushing leakage.Serious corrosion and perforation occurred on the head and tube bundle of regenerated gas heat exchanger E-303 in 800,000 light hydrocarbon plants in Liaohe Oilfield,which seriously affected the normal and safe operation of light hydrocarbon plants.In this study,the gas source and corrosion environment of the heat exchanger were studied by on-site investigation and collection of 4 gas samples and 11external gas samples inside the light hydrocarbon plant.The results show that all the gas samples contain oxygen and carbon dioxide.These corrosive media in natural gas can cause corrosion of steel in the heat exchanger and affect the normal operation of the equipment.The corrosion products of high temperature inlet tube bundle,low temperature outlet tube bundle,high temperature inlet of head,low temperature outlet of head,high temperature of sieve plate Entrance,sieve plate low temperature outlet,inlet valve and outlet valve of heat exchanger were collected on site.The composition of elements and compounds of corrosion products were analyzed by XRF and XRD techniques.The results show that the corrosion product composition of each part is basically the same,mainly containing iron and sulfur elements,and the sulfur element mainly appears in an amorphous state.The corrosion products are mainly Fe₃O₄,and a small amount of Fe₂O₃ and FeOOH are present.The effects of oxygen,carbon dioxide and temperature on the corrosion of heat exchanger head Q345D steel were investigated by using potentiodynamic polarization and SEM.The results show that the concentration of oxygen and carbon dioxide and the temperature will affect the corrosion of steel.However,by comparing the self-corrosion current density of the polarization curve,it can be seen that temperature has the greatest influence on the corrosion of steel.The concentration of oxygen and carbon dioxide is directly proportional to the degree of corrosion of the steel,and the damage caused by oxygen to the steel is greater than that of carbon dioxide.Oxygen mainly causes local corrosion of steel ulcers and small pores,and the distribution is relatively concentrated;Carbon dioxide mainly causes overall corrosion of steel and severe local corrosion.The range of corrosion pits is large and the distribution is relatively uniform;Temperature can cause serious damage to steel,but the corrosion process is affected when the temperature is greater than the boiling point of the solution.The FLUNET software was used to simulate the erosion and corrosion of heat exchanger tube bundles and heads caused by flow velocity.The simulation results show that the shear force on the inner wall of the bundle increases with the increase of the flow velocity,indicating that the flow velocity can promote the corrosion tendency of the inner wall of the bundle.The simulation analysis of the flow pattern also shows that the flow velocity scouring causes the high temperature inlet baffle corrosion of the head,which is more serious than the low temperature outlet of the head.Finally,using the potentiodynamic polarization combined with SEM,the corrosion of the eight steels to be selected in the simulated working conditions was studied.By comparing the self-corrosion current density and corrosion micro-morphology of each steel,combined with the actual situation and economic benefits,316L stainless steel was selected as the substitute steel for the heat exchanger tube bundle from the eight steel materials to be selected,and relevant protective countermeasures were proposed.