Potentiodynamic Reactivation Method for Detecting Sensitization in AISI 304 and 304L Stainless Steels

Abstract

Electrochemical methods have been proposed as a nondestructive, quantitative means for determining the degree of sensitization associated with the chromium-depleted zones surrounding precipitates of chromium carbides in stainless steels. The use of one such method, the electrochemical potentiokinetic reactivation (EPR) test, has been investigated on AISI 304 and 304L stainless steels. Its reproducibility, the effects of scan rate, solution temperature, surface finish, and nonmetallic inclusions were examined. Measurements made with the EPR method were compared with those obtained with the oxalic acid etch test, the ferric sulfate - 50% sulfuric acid test, and the copper sulfate -16% sulfuric acid test of ASTM A 262. Both the EPR and the oxalic acid etch test are nondestructive and can therefore be applied to equipment in the field. It was found that the reproducibility of the EPR test is good and that comparable results can be obtained with a variety of instruments. Results obtained from a round robin ASTM test program are included. The EPR test provides a sensitive, nondestructive, quantitative measure of relatively small degrees of sensitization to intergranular attack. However, when at least some of the grains are completely surrounded by carbide precipitates, the EPR test is less sensitive (it “saturates”) in differentiating between a range of degrees of sensitization than are the ferric sulfate or copper sulfate tests. Even though it is not a quantitative test, the oxalic acid etch test can also be used as a nondestructive method for identifying material which is free of carbide precipitates, i.e., completely free of sensitization.

Quantitative Evaluation of Aged AISI 316L Stainless Steel Sensitization to Intergranular Corrosion: Comparison Between Microstructural Electrochemical and Analytical Methods

“…The selection of the DL-EPR test as a quantitative method for DOS evaluation is hampered by the identification, for each alloy, of the appropriate electrolyte composition, the operating temperature, the potential limits, and the potential scanning rates. [2,5,7,12] In fact, the DL-EPR responses are widely dependent on these operating conditions.…”

Accelerated corrosion of stainless steel in thiocyanate-containing solutions

“…For the single-loop EPR test, a reactivation scan is applied from the passive region to the active region and a reactivation loop is generated during the scan, shown in Figure 4 [19]. The area under the loop gives the amount of charge associated with the dissolution of Cr-depleted area.…”

“…The ratio of the peak current densities of the two loops (Ir/Ia) is used to indicate the degree of sensitization. [19]. [12].…”

Progress report on the results of testing advanced conceptual design metal barrier materials under relevant environmental conditions for a tuff repository

“…Sensitized microstructures give a polarization transient with a shape that is significantly different from that of nonsensitized structures, and integration of the area under the curve is quantitatively proportional to the amount of grain boundary area attacked. These electrochemical tests are called Electrochemical Potentiokinetic Reactivation (EPR) tests (Majidi and Streicher, 1984).…”