Research Of Passivation Process Before The Installation Of The Power Plant Steam Pipe

In China, the process in New power plants takes long time that the electrical equipmentfrom backup protection in pre-produce to normal using after debugging, resulting in a rangeof issues, such as electrical equipment was seriously corrosion before the commissioning,electrical equipment can not be put into use immediately after production, so looking for aneasy use, simple operation, energy saving and environmentally friendly green cleaningpassivation process is imperative. At the same time, combing with the conditions, treat somesteam equipments with a one-time pickling passivation process, for example, the ones whosequality is less demanded, the ones which have smaller capacity of the boiler unit and otherswhich infrastructure to the production time interval is shorter. How to combine the actualconditions, use different acid passivation process, if the liquid waste after the chemicalcleaning can meet the requirement in <The Thermal Power Plant Cleaning Guide>, thisbecomes very important and urgent issue.The topic makes A20carbon steel as the object of study, broadening the pickling thinkingoptimizing the experimental process. In experiments, we select the optimized corrosioninhibitor compound and green passivation process conditions by using static coupon methodand the orthogonal test, at the same time, we analyze the inhibition mechanism of thecompound inhibitor by using scanning electron microscopy (SEM) and EDS test. Then,during the Copper sulfate drip experiment, we detect passivation film quality by the use of theneutral damp heat test, and decide the merits of the passive film corrosion resistance by theuse of the potentiodynamic polarization curves and AC impedance technology.The results show that: in a concentration of5%hydrochloric acid solution, compoundinhibitor showed good corrosion performance by orthogonal test, the best formula is:methenamine10g/L thiourea0.1g/L,30mg/L, and imidazoline op20mg/L, inhibitorcompound inhibition rate could reach97.5%. We observe the surface morphology ofcompound inhibitor by scanning electron microscopy, and think that inhibitor compound wellreduce the general corrosion of steel specimens in the acid solution, whose surface is uniformand smooth after pickling and whose scratches is still in before the experiment. We considerthat there is no residual corrosion inhibitor on the pickling metal surface by electronspectroscopy test, indicating that the corrosion mechanism of inhibitor is the physicaladsorption. By improving the passivation of hydrogen peroxide process in <The ThermalPower Plant Cleaning Guide>, we solve two problems, one is that in the passivation process,the passive film quality of the hydrogen peroxide is bad; the other is that in the passivation process, the hydrogen peroxide easily produces the second floating rust; reduce hydrogenperoxide passivation temperature, simplify the process operation. The performance is in linewith national standards, and the passivation film quality rated as excellent. Final, thepassivation process of the hydrogen peroxide is sure as follows: concentration of thehydrogen peroxide is0.4%, concentration of trisodium phosphate is3g/L, triethanolamine2ml/L, the passivation solution temperature is40℃, pH value is9.2, the passivation time is6hours.In one-time pickling passivation experiment, the subject is a research of simplifyprocesses, which is about the small boiler and the chemical cleaning before the installation ofthe steam pipe prior, by using the idea of pickling and passivation completed at the same time,namely, in the pickling process, a layer of protective film can be formed on the metalsubstrate surface, which can not only prevent the metal matrix continue to dissolving in theacid, but also prevent the metal body surface producing the secondary corrosion in the openatmospheric environment. According to the above question, we use Hydrochloric acid-phosphoric acid mixed acid lotion to remove the metal surface oxide while using methylamineas a corrosion inhibitor to prevent excessive corrosion of metal in the pickling liquor, sodiumpolyphosphate added to improve the corrosion resistance of the overall carbon steel. Theresults show that: optimum conditions of one-time pickling passivation as follows: theconcentration of hydrochloric acid is5%, the concentration of phosphoric acid is12%,compound corrosion inhibitor Utopia products9g/L, sodium polyphosphate3.5g/L, theexperimental time is two hours. Style after the pickling passivation by copper sulfate dripexperimental takes6.2s neutral damp heat test for49h, indicating disposable picklingpassivation process greatly increase in the corrosion resistance of the carbon steel.During the electro-chemical tests, compared with the carbon steel which was notprocessed, the steel corrosion potential of the carbon steel which was passivated was shiftedpositively, the corrosion current was significantly reduced, the metal surface impedance wasincreased, from350to8K, indicating the trend of secondary corrosion of the style afterpassivation was significantly reduced, which reflects the results of the experiment isconsistent with the copper sulfate drip and neutral hot and humid experiment.