Abstract
Double Loop-Electrochemical Potentiokinetic Reactivation (DL-EPR) is a valuable technique to test Type 304 stainless steel (SS) materials and components for the presence of grain boundary chromium depletion and assess material sensitization. This has practical relevance for the evaluation of susceptibility to intergranular stress corrosion cracking (IGSCC) of welded structures. The present study reports on work to develop DL-EPR methodology applied to UNS S30400 SS pipe butt-welds of relatively small size and having fusion zones irregular in shape, both of which present experimental difficulties to electrochemical evaluations. The primary challenge was to determine how to practically get an accurate DL-EPR signal from the relatively small heat affected zone (HAZ) that may be susceptible to IGSCC. A simple method was used to isolate the area of study that led to a relatively small solution potential drops during DL-EPR measurements. Measurements on a control material showed that smaller IR drops correlated directly with a measurably smaller degree of sensitization as measured by DL-EPR. A prototypic butt-weld was used to join two different heats of materials, one of which had a low carbon with high delta-ferrite content and the other of which had a high carbon content and no delta-ferrite. The DL-EPR process could detect the delta-ferrite in the low carbon material and also isolate DL-EPR degree of sensitization measurements to the HAZ of the high carbon material. In the process of this DL-EPR analysis, comparisons were made with two different grain boundary etch techniques.
