EFFECT OF UNCOMPENSATED IR-DROP ON POLARIZATION RESISTANCE MEASUREMENTS

A theoretical analysis of the effect of uncompensated IR-drop on polarization resistance (R//p) measurements is given, which shows that it is not the absolute value of the solution plus surface film resistance (R// OMEGA ) which determines the error due to IR-drop, but the ratio (R// OMEGA /R//p). An error is possible even in solutions of moderate to high conductivity, if corrosion rates are high. The experimentally determined polarization resistance (R//p) is the sum of the true polarization resistance (R//p) and the ohmic resistance (R// OMEGA ). If no corrections are made, polarization resistance values will be determined too high and consequently corrosion rates will be found too low. The effect of uncompensated IR-drop on measured polarization curves is shown. Experimental data with and without IR-drop compensation ( ″positive feedback″ ) confirm the theoretical considerations.