Study On Corrosion Failure Mechanism Of Material In Heat Exchanger Pipeline Under Alkaline Environment

The status of heat exchangers is very important in etrochemical enterprises,it’s a necessary part of the production process.In practice,however,heat exchangers often have various kinds of faults,the failure of heat exchangers caused by corrosion failure accounts for more than half of the total failure of heat exchangers.Therefore,to master the corrosion failure law of heat exchangers and carry out effective anticorrosion measures to ensure the normal operation of heat exchangers has become a very important issue for petroleum refining enterprises.In this thesis,the corrosion failure mechanism of material in the heat exchanger pipeline under alkaline environment is studied by combining with the corrosion perforation phenomenon of the oxide alkali heat exchanger.NaOH solution was selected for corrosion medium.(1)The micromorphology,macromorphology and metallography of samples was analysed by optical microscopy and scanning electron microscopy.The analysis shows that the external corrosion of the heat exchanger tube is more serious than the inner one,the corrosion products are mostly oxide of Fe,and there are less corrosion products in the inner wall of pipeline and more corrosion products in the outer wall of pipeline.The corrosion development direction of the corrosion hole is from the corrosion hole to the surrounding and from the outside to the inside of the pipeline.(2)The effect of the temperature and concentration of NaOH on the corrosion behavior of 10 carbon steel was studied through potential dynamic method and electrochemical impendance spectroscopy.The surface corrosion morphology of the specimen was observed through optical metallographic microscope.It indicated that the corrosion current density of 10 carbon steel increased with the increase of temperature and concentration of NaOH solution,meanwhile,the corrosion potential and the stability of passivation film decreased.The corrosion degree increased.when the concentration of NaOH was ≥ 30%and the temperature was ≥ 40℃,the corrosion mechanism was changed and the corrosion degree of the specimen was obviously deepened.(3)An experimental study on the flow corrosion of 10 carbon steel in NaOH solution was carried out by means of a multi-function corrosion test device designed and manufactured by the author.Through the analysis,it is found that with the increase of temperature and concentration,the corrosion degree of the specimen increases and the corrosion rate increases.At 10%concentration,the passivation film is stable,corrosion resistance is good and corrosion rate is low.Under the condition of 20%concentration,although the corrosion of the sample is not serious,the passivation film is not stable,there is a hidden danger of serious corrosion.When the concentration reaches 40%,even at low temperature(30℃),the specimen can also have serious corrosion.