Study On Corrosion Behavior Of Q235Steel At Low Temperature Parts Of Crude Oil Distillation Unit

With China’s crude oil into the late,increasing the stock of high-quality crude oilresources is reduced, a large number of low-quality crude oil,especially high acid (0.5~1.0mg/g) heavy and high-sulfur (1%to2%) imported crude oil processing volume increasing.Because crude oil contains a high acid value, sulfur and salt, often due to corrosion and otherreasons cause corrosion of atmospheric and vacuum distillation unit, seriously affecting thenormal operation of equipment.Causes corrosion of atmospheric and vacuum distillation unitfor analysis, so look out for countermeasures technology has become a very important issue.In this paper, the static coupon weight loss, polarization curves, scanning electron microscopyand X-ray diffraction analysis were investigated on Q235steel corrosion behavior in formicand acetic (the weight ratio of formic and acetic is1:1), hydrogen sulfide and ammoniumchloride aqueous. Were investigated different etchant concentration, temperature and othercoupon corrosion behavior of Q235steel case.Study on the corrosion behavior of Q235steel in aqueous solution of formic and acetic(the weight ratio of formic and acetic is1:1）showed: Q235steel corrosion rate in solution offormic and acetic in a90℃temperature range, the average corrosion rate of Q235steel inaqueous solution of formic and acetic was increased with the rise of temperature, when theconcentration is100mg/L, the average corrosion rate by20℃,0.354mm/a to90℃,1.255mm/a;In the500mg/L etchant concentration range, the average corrosion rate of Q235steel inaqueous solution of formic and acetic was increased gradually at first and then leveled off withconcentration increases, when the temperature is20℃, the average corrosion rate by100mg/L,0.354mm/a to500mg/L,0.900mm/a. The macroscopic morphology of corrosion was uniformcorrosion, while severe corrosion, localized pitting, peeling and other phenomena. Byanalyzing the corrosion kinetics shows that this reaction are first-order reaction, the activationenergy of the reaction was27.33KJ/mol.Study on the corrosion behavior of Q235steel in aqueous solution of hydrogen sulfideshowed: Q235steel corrosion rate in a separate aqueous solution of hydrogen sulfide isrelatively small, under the experimental conditions, the maximum is only1.712mm/a, when50℃and600mg/L, this is because the Q235steel in an aqueous solution of hydrogen sulfide corrosion products mainly FeS, on Q235steel has a protective effect. Q235steel corrosion ratewith increasing concentrations of hydrogen sulfide increases after the first showing adecreasing trend, this is because when the hydrogen sulfide concentration of600mg/L, therelative content of the product Fe9S10maximum of Q235steel protection the degree ofweakening.Study on the corrosion behavior of Q235steel in aqueous solution of ammonium chlorideshowed: Q235steel corrosion in aqueous ammonium chloride belongs to salt corrosion,mainly by hydrolysis of NH4+produces H+result electrochemical corrosion, corrosion rate ofQ235steel occurs relatively small. The main product was FeCl2, the corrosion rate withincreasing concentration of etching solution and the temperature is higher. Corrosionmorphology is essentially uniform corrosion.On the corrosion behavior of Q235steel in hydrochloric acid and ammonium chloridemixed aqueous solution studies showed: Q235steel corrosion in hydrochloric acid andammonium chloride mixed aqueous solution, the acid corrosion is mainly, hydrochloric acid isa strong acid, causes Q235steel severe corrosion, because the resulting product is chlorideiron. It dissolves in water, does not have a protective effect on Q235steel. The corrosionmorphology is typical of intergranular chlorine corrosion.