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ASTM G59 Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements
Last updated November 12, 2025
ASTM G59 Standard Test Method for Conducting Potentiodynamic Polarization Resistance Measurements
ASTM G59 is an international standard for measuring the polarization resistance of metallic materials using potentiodynamic polarization. This is an electrochemical method used to measure corrosion rate by monitoring the current-potential relationship near the corrosion potential. It has found specific use in measuring homogeneous corrosion behavior in conductive solutions without causing severe damage to the specimen. The technique is rapid, accurate, and can be used with a variety of metals and alloys. Using ASTM G59, scientists and engineers can compare corrosion behavior, assess the effectiveness of inhibitors, and analyze the influence of environmental factors on material behavior across different industrial environments.
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ASTM G59 Introduction
In material engineering, corrosion is a major issue that determines the service life and safety of metallic structures. ASTM G59 describes a potentiodynamic method of polarization resistance, which is a significant measure of the corrosion rate in controlled electrochemical conditions. This technique gives fast and accurate data, as it scans the potential in a small range around the open-circuit potential, as opposed to long-term immersion tests. The polarization resistance is obtained through the slope of the potential-current curve and may be used to determine the rate of corrosion using the Stern-Geary equation. This technique finds extensive application in corrosion studies, corrosion inhibitor studies, and also in the selection of materials to be used in hostile industrial settings.
ASTM G59 Test Method
Electrochemical Cell Arrangement
The system consists of three electrodes, where the working electrode (test specimen), the reference electrode (usually Ag/AgCl or saturated calomel), and the counter electrode (platinum or graphite).
Potential Scanning
The potential of the working electrode is scanned at a slow rate (usually within ±20 mV of the corrosion potential) to establish quasi-equilibrium.
Measurement at the Present
The current is measured as the rate of change of potential, and the relationship between current and potential is plotted to produce a polarization curve.
Data Analysis
The slope of the linear portion of the polarization curve yields the polarization resistance (Rp), which is directly related to the inverse of the material’s corrosion rate.
ASTM G59 Sample Preparation and Equipment
Preparation of Sample
The sample must be prepared from the metal or alloy being studied and kept as smooth as possible and polished. The average exposed area is approximately 1 cm2, which gives a consistent distribution of current.
Handling and Cleaning
The sample should be rinsed using deionized water before testing, after being cleaned with acetone or ethanol to remove grease. The surface oxides can be eliminated either by mechanical or chemical means in order to have a valid electrochemical contact.
Equipment Arrangement
The test cell should have a potentiostat or galvanostat capable of fine control of potential and current measurements. An electrolyte solution, which is commonly a simulated corrosive medium such as 3.5% NaCl, is expected to be held at a constant temperature (usually 25 ± 1 °C) to ensure reproducibility.
ASTM G59 Results and Interpretation
The major outcome of ASTM G59 testing is polarization resistance (Rp), which is in ohm/cm 2. Based on Rp, the corrosion current density (Icorr) and rate of corrosion can be determined by using the developed electrochemical relationships. High polarization resistance is the sign of low corrosion activity, which is a strong material performance or a good inhibitor. On the other hand, a low Rp value implies a faster rate of corrosion and weaker material resistance. The straight line part of the polarization curve towards the corrosion potential indicates a uniform corrosion process, and deviations are possible indications of local corrosion or passivity. The method is therefore a quantitative and sensitive way of measuring corrosion kinetics in metallic materials.
ASTM G59 is closely related to a number of corrosion testing standards in the electrochemical test. ASTM G102 provides the calculation protocol for electrochemical corrosion rates, which are used in addition to data measured using G59. ASTM G61 describes cyclic potentiodynamic polarization testing to be used in the study of localized corrosion, e.g., pitting or crevice formation. ASTM G5 encompasses potentiodynamic anodic polarization techniques for general corrosion research, whereas ASTM G150 is on critical pitting temperature testing of stainless steel. Collectively, the standards constitute a comprehensive package for corrosion resistance assessment, enabling industries to develop and certify materials that perform better under different environmental and electrochemical conditions.
ASTM G59 Applications in Industry
ASTM G59 finds extensive use in the industry that uses metallic materials in corrosive environments, including oil and gas, marine, automotive, and energy sectors. It is applied in assessing the capability of corrosion inhibitors, coatings, and protective treatments. The test would help in the comparison of alloy compositions and heat treatments in the development of materials in order to determine corrosion-resistant formulations. It is also used in water treatment systems, pipelines, and chemical processing units to control and reduce corrosion damage. ASSTM G59 is used in industrial applications in predictive maintenance, materials optimization, and enhanced durability by offering fast and accurate data on corrosion rate.