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Scope

1.1 This test method covers a procedure for conducting anodic polarization studies to determine the crevice repassivation potential for corrosion–resistant alloys. The concept of the repassivation potential is similar to that of the protection potential given in Reference Test Method G 5.

1.2 The test method consists in applying successively potentiodynamic, galvanostatic, and potentiostatic treatments for the initial formation and afterward repassivation of crevice corrosion.

1.3 This test method is a complement to Test Method G 61.

1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Significance and Use

The THE test method is designed to provide highly reproducible crevice repassivation potentials for corrosion–resistant alloys (for example, Alloy 22) in a wide range of environments from non-aggressive to highly aggressive. In conditions of low environmental aggressiveness (such as low temperature or low chloride concentration), corrosion–resistant alloys such as Alloy 22 will resist crevice corrosion initiation and the cyclic potentiodynamic polarization test (Test Method G 61) may fail to promote crevice corrosion mainly because it drives the alloy into transpassive dissolution instead of nucleating crevice corrosion. The THE test method provides a more controlled way of applying the electrical charge to the test electrode, which may induce crevice corrosion without moving it into transpassive potentials.

The more noble this crevice corrosion repassivation potential (ER,CREV) value, the more resistant the alloy is to crevice corrosion in the tested electrolyte. This is similar to other test methods to measure localized corrosion resistance such as Test Method G 61 and Test Methods G 48. The results from this test method are not intended to correlate in a quantitative manner with the rate of propagation that one might observe in service when localized corrosion occurs.

This test method may be used to rank several alloys by using the same testing electrolyte and temperature. It can also be used to determine the response of a given alloy when the environmental conditions (such as electrolyte composition and temperature) change.

Keywords

corrosion–resistant alloys; crevice repassivation potential; electrochemical test; ICS Number Code 77.060 (Corrosion of metals)

To find similar documents by ASTM Volume:

03.02 (Corrosion of Metals; Wear and Erosion)

To find similar documents by classification:

77.060 (Corrosion of metals Surface treatment and coating, see 25.220)

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