Study On Corrosion Behavior Of T/P92Heat-resistent Steel

With the continuous development of thermal power units to large capacity, highparameter, operation parameter increases. Superheater and reheater in high parameter thermalpower units suffer the most hostile environment with the highest requirements ofmaterial.The material has to satisfy the enduring strength, creep strength, corrosion resistanceand resistance of pipe smoke fly ash erosion.The inner wall of the tube must also be satifiedthe requirements of steam oxidation resistance and good processing properties of hot-coldand welding performance.High temperature and high pressure environment made the superheater pipe prone tostress corrosion, high temperature oxidation of high-temperature steam environmentprompted the superheater pipe, the outside of the tube in high temperature flue gas erosionenvironment. Moreover, during salt accumulation of super-heater, some components of saltin high temperature conditions can accelerate corrosion of the pipeline, so that the rapidthinning occure at salt accumulation position,even the tube explosion.This paper takes T/P92new heat resistant steel as the research object, by the electrochemicalworkstation, autoclave lined with polytetrafluoroethylene, muffle furnace were used to studythe corrosion behavior of material. By using Tafel polarization curves and AC impedancemethod by application of electrochemical workstation, the information about corrosion rateand mechanism were acquired; The autoclave was mainly used to simulate the environmentunder high temperature and high pressure,research the corrosion of materials with differentcorrosion solutions, The use of autoclave lined with polytetrafluoroethylene can removeinterference of dissolved metal ions in the reactor.Experiment of coating salt simulatesuperheater salt accumulation by using muffle furnace to finish the researchThe electrochemical experiments drew the following conclusions: Icorr and Rct with theincreasing of pH first increased and later decreased, the biggest value appeared in pH=9.00.With the increase of concentration and temperature, Icorr increased, Ecorr negative, Rctdecreased, T/P92material increased in varying degrees of corrosion.The autoclaveexperiment were concluded: at pH8¹1sodium hydroxide solution, when the pH=9the corrosion rate of P92steel maximum; increased with the content of chlorine ion in differentconcentration sodium chloride solution, the corrosion degree of material increasedsignificantly; Through metallographic analysis on the specimen surface corrosionmorphology found that in sodium hydroxide solution, T/P92heat-resistant steel mainlyoccurred uniform corrosion; In sodium chloride solution, T/P92heat-resistant steel mainlyoccurred pitting corrosion; High temperature coated salt test draws the followingconclusions:the corrosion occurred by the NaCl for T/P92material was stronger than theequivalen Na₂SO₄at600℃. The corrosion products of T/P92heat-resistant steel arecomposed of corrosion layer loose and tight inner layer near the substrate. The maincomposition of corrosion products on the surface are Fe₂O₃, Fe₃O₄and FeCr₂O₄.The sectionmorphology and EDS spectra of corrosion products showed that: The addition of Cl canproduce a lot of bulging pit in corrosion products, greatly accelerate the corrosion of T/P92material, S, Cl can penetrate the corrosion surface inward penetration.