The Study Of Closed Cooling Water System Corrosion Inhibition

There are many kinds of heat exchangers, pipes and valves in the power plant closed cooling water system. Due to the great lose of economic were caused by corrosive perforation and leakiness, corrosion protection is very important for the closed cooling water system.The phosphate is common used to reduce corrosion in closed cooling water system in QinShan phaseΠ, the phosphate concentration is controlled at 100⁵00mg/L, pH is controlled at 11.0¹1.5, Fe ion is controlled at less than 1.0 mg/L. This method is running under high pH conditions by using alkaline phosphate, the steel will polarize due to the dissolved oxygen (DO), and the protection film will come into being on the surface of steel, which will reduce the corrosion. But the buildup time for the film is a little long, before the film completion, the electrochemistry corrosion will continue happen, so it's very difficult to control the corrosion rate, the operation analysis data shows that the effect of corrosion inhibition was not good, the total Fe in system keep increasing, the Fe ion in the water will greater than 1mg/L in one month.In order to solve the corrosion problem in closed cooling water system, base on the study and researching of other power plant, this article suggests the nitrite inhibitor N8338 to replace the current phosphate. the nitrite inhibitor will generate compactγ- Fe₂O₃ polarization film to prevent corrosion.The static hang-up specimen, electrochemistry polarization curve and electron microscope scanning will be used to study the material, to further confirm the effect of the nitrite inhibitor performance and compatibility with other materials in closed cooling water system in QinShan phaseΠ, to provide the more information for the inhibitor. According my study, the conclusion lists as following:(1) N8338 inhibitor has inhibition to TUE250 carbon steel,austenitic Spheroidal graphite iron, martensite stainless steel and titanium, which has obvious inhibition to TUE250.(2) N8338 inhibitor has effective corrosion inhibition to TUE250 carbon steel. Under the static hang-up specimen testing, the inhibition efficiency is more than 95.0% when the N8338 concentration is at 200⁹00mg/L, Under the polarization curve testing, the inhibition mechanism for N8338 is mainly to inhibit anode corrosion.(3) The inhibitor N8338 can prevent martensite stainless steel, titanium and austenitic Spheroidal graphite iron from corrosion. The impurity ion of F^-,Cl^-,SO₄^2- addition to demineralize water with 700mg/L N8338, the result shows that there is no obvious effect to the corrosion of material.Most of materials used in closed water system is TEU250 carbon steel in QinShan phaseΠ, So the TEU250 carton steel is placed emphasize on the corrosion , according testing result, N8338 inhibitor has effective inhibition corrosion to TUE250carbon steel, so it's practical to use N8338 inhibitor to replace the phosphate.