Inhibition of Steel Corrosion in Edta Solution by N, Scompounds

摘要

In recent years alkaline process became a major technique for chemical cleaning of boilers used in fossil power plants in Taiwan. Mild alkaline salts (e.g., various ammonium salts of 12% ethylenediaminetetraacetic acid, EDTA) were used rather than severely corrosive acids. However, it needs a more complicate technology involving tWo-stage operation and critical control of temperature in each stage. Corrosion inhibitors such as N, S-heterocyclic organic compounds were introduced into the boilers prior to alkaline cleaning to ensure complete prevention of steel. First stage of the process was conducted at 120- 150 ～C for hematite removing and the second was carried out at temperatures less than 65℃ for copper removing. Coupon test and electrochemical study were explored for double check. Electrochemical measurements in corrosion potential, polarization resistance and Tafel plot are compared to estimate the inhibition efficiency of the inhibitors. The inhibition efficiency (%IE) decrease in the order: 2- mercaptobenzothiazole (91%) > benzotriazole (84%) > 2-mercaptobenzimidazole (83%) > benzothiazole (81%) > indole (60%) > benzimidazole (59%). The result of coupon test is in agreement with that from electrochemical study. The inhibition efficiency increases with increasing the inhibitor concentration but decreases with increasing the temperature from 120 to 180℃. Langmuir absorption isothermal is obeyed in the inhibiting system. The activation energy is much higher in the inhibiting than the un-inhibiting system.