The use of interphase capacitance in evaluating the effectiveness of corrosion inhibitors

摘要

SOME GENERAL considerations about the acid cleaning of steam generators in thermal power plants are given, and the importance of specific corrosion inhibitors in restraining corrosion rates of carbon steels is stressed. The use of interphase capacitance as a suitable parameter for evaluating the inhibitor effectiveness and chemical stability of organic compounds was examined in the case of iron and two carbon steels interacting with 5 percent wt HCI solution at temperatures ranging from 65 to 90 deg C and containing a proper corrosion inhibitor at various concentrations.Alternating current measurements were performed over the 0.08-2 X 10~4Hz frequency interval under current control by imposing for each experimental point the constraint 4 <_0 < 6mV RMS, and adopting a suitable integration time. The value of the interphase capacitance was computed over the 4 X 10~3-2 X 10~4Hz frequency range using various mathematical schemes in order to verify the validity of the equivalent electrical network. The main result is that small values of the double-layer capacitance are associated with high performance in corrosion inhibitors. On the other hand, the increase in time of the capacitance value indicates a decrease of the chemical stability of the inhibitor.