Study On Corrosion Behavior Of T91 Materials Used As Overheating Tubes Of Plant Power

Along with the increase of our country the power plant boiler equipment capacity and steamparameters, then more and more of the boiler pipe explosion accident happened. Statisticalpower station boiler accidents founded that the damage blasting leaks of in heating tube（water-wall tubes, overheating pipes, reheater pipes, economizer tube, say again "four tubes"）was the most serious and widespread.For the overheating pipes under high temperature andhigh pressure steam, the main factors of pipe explosion was oxidation and corrosion, theoxidation resistance and corrosion resistance were important indexs. T91 steel as the mainmaterial of overheating pipes, the study of the corrosion behavior and corrosion mechanismwas very necessary.The passivation, erosion and acid corrosion corrosion behaviors and characteristics of T91wasstudied in this article. Electrochemistry test methods and suspended coupon experiment wereused to obtain corrosion rate,the corrosion inhibitor rate and related datas, included Tafelpolarization curve, Electrochemical impedance spectroscopy, Electrochemical noise,specially,and using SEM、XRD、EDS to test the surface of the specimens.This paper studied found that:（1）The corrosion behavior of T91 steel was studied fromdifferent pH values and temperatures, The best corrosion resistance points of T91 steel waspH=9. Setting the pH value of solution was 9,the experiment of electrochemical and hangpiece were did in different temperature and different concentration of Cl^-、SO₄^2- solutions forT91 steel. Contrasted results of Icorr、Vcorr、Rct, SO₄^2- than Cl^- the corrosion affect larger of T91steel under the same conditions.（2） Different concentrations of sodium nitrite was choosed forpassivation solution.In different temperature and pH value conditions of T91 steel forpassivation, through the electrochemical and copper sulfate titration experiment, The best passivation T91 steel condition was: 30℃, pH 9.5, concentration of NaNO₂was 0.5%. T91was eroded in 1.0mol/LNaCl after the best passivation treatment. Contrasted of theexperimental data before and after the passivation, Icorrvalue reduced two orders of magnitude,Ecorrpositive moved, Rctvalue also increased one order of magnitude. Passive film effectivelyreduced the Cl^-to the erosion of T91 steel.（3） The electrochemical experiments of rustycoupon of T91 was tested in the 16% hydrochloric acid, Drawed potential-time figure.Foundthat when the derivative value of the potential was Zero, the derusting effect was the best ,Judged for pickling end at this time．When the mass fraction of hydrochloric acid was higherand the temperature of pickling was higher,the pickling time was shorter．Due to the strongvolatile of hydrochloric acid , it can be got that the optimum pickling temperature was50℃,and the optimum mass fraction of HCl which was used to pickling was 16% based onthe experimental results and fitting curve equation．The experiment found that there weresome corrosion inhibition of T91 steel when added a certain amount of poly epoxy succinicacid（PESA） into 16% hydrochloric acid solution,.The inhibition efficiency of PESA increasedwith the increasing concentration, decreased with the increasing temperature, The inhibitingrate remain unchanged when PESA concentration more than 20g/L. PESA conformed toLangmuir adsorption isotherm. So PESA used not only in alkaline conditions, but also used inacid conditions.