Abstract
The behaviour of four commercial inhibitors used for the pickling baths and acid cleaning of steam generators in thermal power stations has been investigated and their inhibitor effectiveness has been determined both with gravimetrical tests and with electrochemical measurements. The latter have shown that a complete surface impedance diagram on Argand's plane is very helpful in discriminating the behaviour of a given corrosion inhibitor, quantitatively as well as qualitatively.
In addition, numerical elaboration of the polarization curves has revealed that corrosion current density gives a satisfactory reproduction of the real behaviour of the metal sample only for one commercial inhibitor. Use of the polarization resistance, however, has proved to be a valuable means of evaluating the inhibiting power. Within the concentration interval of practical interest, polarization resistance has yielded the same results as the gravimetric tests.
A very interesting observation is that all four products exhibit a constant efficiency over a fairly wide concentration interval. This is of considerable importance because it is our opinion that the concentration of the inhibitor is never homogeneous during acid cleaning.
