MaTestLab > ASTM Methods > Metals and Alloys Testing > ASTM G61 Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
Last updated 3rd November 2025
ASTM G61 Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
ASTM G61 is the standard for measuring the localized corrosion susceptibility of alloys of iron, nickel, and cobalt using cyclic potentiodynamic polarization (CPP) tests. This is an electrochemical technique that provides a fast way to determine an alloy's resistance to pitting and crevice corrosion in a hostile environment. The test quantifies the present response of a metal surface when a cycling of the potential is done in the anodic direction and then reversed to identify important potentials like pitting, passivation, and corrosion potential. This technique is common in corrosion studies and in the qualification of materials that are deemed to perform well in a chloride-rich or oxidizing environment.
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ASTM G61 Introduction
ASTM G61 is a standardized electrochemical technique for characterizing such corrosion behavior in terms of cyclic potentiodynamic polarization. Localized corrosion, such as pitting and crevice attack, is a significant threat to the long-term performance of metallic materials in chemical, marine, and industrial conditions. The test gives useful information on the initiation and repassivation pit tendencies of an alloy that is numerically useful in measuring susceptibility. This method is used to supplement the old-fashioned tests of immersion and salt sprays because it allows quick screening in a controlled laboratory environment. It is especially implemented to compare alloy composition, surface finish, and environmental impact on corrosion resistance.
ASTM G61 Test Method
Principle
The specimen is dipped into an electrolyte of known composition and hooked up to a potentiostat. Potential scanning is done between the open-circuit potential (OCP) in the anodic direction to a given limit, and corrosion occurs locally. A scan is made in the opposite direction to the cathodic direction. The point of crossing of forward and reverse curves gives an understanding of pitting and repassivation behavior.
Procedure
A constant scan rate of 0.6 mV/s is held constant until the current density starts rising rapidly, and this is a sign of pit initiation. This potential is then reversed to the point of reduction in current density, demonstrating repassivation. A cycle polarization curve is obtained, and key electrochemical parameters, such as corrosion potential (E corr ), pitting potential (E pit ), and repassivation potential (E rep ), are determined.
ASTM G61 Equipment and Sample Preparation
Specimen Details
The test specimen is usually a flat piece of metal of the alloy to be tested, of a specified area of exposure (such as 1 cm²). Some of the materials that have been tested are stainless steel, nickel-based, and cobalt-based materials.
Specimen Preparation
Samples are mechanically polished to a fine finish (usually up to 600-grit) and cleaned ultrasonically in ethanol or deionized water to remove contaminants before testing.
Specimen Dimensions
Nonconductive surfaces are applied to the exposed portion, like lacquer or epoxy, so that the area of the exposed portion is accurately determined, so and the density of the current can be accurately calculated.
Results and Interpretation
The interpretation of results is based on the cyclic polarization curve, where the forward (anodic) and reverse (cathodic) scans suggest the corrosion and the behavior of repassivation of the alloy. A high value of the hysteresis loop indicates that the alloy is susceptible to localized corrosion, whereas a small or zero loop indicates high resistance. The ratio between the pitting and repassivation potential gives the measure of the capability of an alloy to overcome pit initiation. The potential and the density of corrosion current are also useful in estimating the overall rate of corrosion. Alloy grades are compared, surface treatments are evaluated, and environmental resistance is confirmed in design applications by using these results.
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Related Test Methods
ASTM G59 (polarization resistance measurement), ASTM G5 (potentiodynamic anodic polarization measurement), and ASTM G150 (electrochemical critical pitting temperature test).
ASTM G61 Applications in Industry
This method finds many applications in materials research, quality assurance, and corrosion engineering. The petrochemical industry, marine industry, power generation, biomedical industries, and others are all industries that use this test to test the behavior of alloys in the presence of chlorides or acids. It helps to determine the choice of corrosion-resistant alloys in heat exchangers, pipes, reactors, surgical implants, and turbine components. The data are also crucial in coming up with the new alloys and surface coatings with more localized corrosion resistance.
ASTM G61 Materials Commonly Tested
This method can be used in iron-based alloys (such as stainless steel), nickel-based alloys (such as Inconel and Monel), and cobalt-based materials (such as stellite). It is also applicable in a comparative analysis of passivation treatment, coating, or surface-modified material employed in corrosive environments.
ASTM G61 Common Challenges and Troubleshooting
An unstable reference electrode potential is also quite common, together with poor specimen polishing or contamination of the electrolyte. Flaws or cracks on the surface can bring errors that may facilitate early pitting. It is important to make sure that the electrochemical environment and the surface are clean and reproducible. To improve the reliability of data, the equipment should be calibrated, and freshly prepared electrolytes should be used. Test reproducibility and curve reproducibility analysis can be used to test results.
ASTM G61 Safety and Best Practices
Electrolytes that include chlorides, acids, or oxidizing markers must be dealt with carefully, with the aid of the operator using gloves, goggles, and a laboratory fume hood. Proper grounding of electrical connections must be carried out to prevent damage to the device. To avoid contamination, specimens must be rinsed and discarded in conformity with the environmental safety regulations.
Importance of ASTM G61 Test Method
This method is an important device used in the study of corrosion, as it allows the determination in detail of the local corrosion vulnerability of important alloys in engineering. This data assists engineers in choosing the right materials, optimum surface treatment, and a component that is designed with increased resistance to corrosion.
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The required number of samples or specimens should comply with the procedure given in the astm g61 standard. However, the MaTestLab operations team can assist you for your special requirements once you share your testing details with us.
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The turnaround time for astm g61 test methodology depends upon the test procedure mentioned in the standard test document. However, we at MaTestLab understand your research requirements and hence try to get your test completed within the least possible time.
Where can I get the astm g61 tested?
You can share your astm g61 testing requirements with MaTestLab. MaTestLab has a vast network of material testing laboratories, spread across the USA and Canada. We support your all material testing needs ranging from specific astm g61 test to various testing techniques.
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