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The linear polarization resistance method of predicting corrosion behavior was compared directly with weight loss measurements on freely corroding specimens. The estimated weight loss was obtained by calculation from the corrosion current and the polarization resistance. The anodic Tafel constant βa was determined from potentiodynamic curves for mild steel in flowing, oxygen containing, natural seawater. The cathodic Tafel constant βc was calculated by substitution of the corrosion current, the anodic Tafel constant, and the polarization resistance into the Stern-Geary relationship. In subsequent experiments, βa = 0.066 V/decade and βc = 0.077 V/decade were used in all calculations. Although an initial agreement between estimated and actual corrosion rates existed for periods of up to 60 days, long-term studies began to produce “anomalous” data in about 120 days. It was observed empirically that the polarization resistance was semilogarithmically related to the scan rate over three orders of magnitude from 0.001 to 1 mV/s.
corrosion, steels, seawater, corrosion rates, polarization resistance, mild steel, Tafel constants, scan rates, evaluation
Research chemist, Naval Research Laboratory, Key West, FL
Supervisory research chemist, Naval Research Laboratory, Washington, DC,