AbstractSome general considerations on corrosion inhibitors and the basic concepts concerning pickling and acid cleaning of iron alloys are exposed. The thermal stability of a commercial inhibitor, added to 5 by weight HC1 solutions, has been investigated by examining the behaviour of three carbon steels at the temperatures of 65, 75 and 85°C under dynamic conditions, the solution velocities being 0.5, 1.0 and 1.5 ms−1. Experimental results pointed out that SA 106 grade B and SA 213 grade T22 steels were prone to localised attacks at a temperature of about 85°C, but this unusual behaviour cannot be attributed to decay products of the inhibitor. In fact, SA 213 grade T11 steel exhibited at the same temperature corrosion of the uniform type. Electrochemical measurements, based mainly on current transients, proved very useful for a qualitative evaluation of the corrosion kinetics, but at present the problem of a faithful representation is still open. The electrochemical determination of the corrosion current density through numerical analysis of polarisation curves, corrected to remove the contribution of the ohmic drop to the electrode potential, was quite different from the mean corrosion rate obtained from the weight loss. Techniques based on alternating current provide a valid tool for evaluating the solution resistance and interphase capacitance and can be used for a qualitative monitoring of corrosion kinetics in the low‐frequency region. The dependence of corrosion rate on temperature was determined using the Arrhenius law. Satisfactory results were obtained only for SA 213 grade T11
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