Pitting and Crevice Corrosion Behavior of the Duplex Stainless Steel UNS S32205 Welded by Using the GTAW Process

Abstract

This study investigated the pitting and crevice corrosion behavior of the gas tungsten arc welding (GTAW) process in the UNS S32205 according to industrial parameters. Results revealed that the welding process presented a weld metal chemical composition similar to the base metal and an adequate balance of the austenite and ferrite phases. No relevant variation in the hardness was observed and XRD spectra did not identify the presence of deleterious phases in the weld bead. Cyclic polarization tests revealed similarities between welded and base metal samples (20±2°C, NaCl 3.5% wt.). When comparing the behavior obtained in the crevice, and pitting tests, a decrease in the corrosion resistance was observed in the presence of a crevice former. The SEM-EDS proved that the attack occurred mainly in secondary austenites. Profilometry measurements revealed that the crevice corrosion in the weld region was deeper than in the base metal. However, considering the welded samples as a unit, making no difference between regions: weld metal, HAZ, and base metal, the average crevice corrosion depth was comparable to that of the base metal samples. Finally, it was concluded that the welding process used for the UNS S32205 steel did not harm its corrosion resistance.

Failure Analysis of Duplex Stainless Steel for Heat Exchanger Tubes with Seawater Cooling Medium

“…This scale was formed by microbiologically induced calcium carbonate precipitation (MICP) [31,33]. The microstructural examination revealed that corrosion attack occurred preferentially along the austenite grains; this phenomenon is common in duplex stainless steel, which typically fails due to crevice corrosion [39,40]. The use of materials that are inappropriate for the heat exchangers' seawater cooling medium conditions is the leading/root cause of this issue.…”

“…A preferential attack on the austenite grain of the weld metal phenomenon was observed during the crevice corrosion test. According to prior studies, preferential dissolution occurs at all morphologies of austenitic phases: grain boundary (GBA), Widmanstätten (WA), and intragranular (IGA) [38][39][40]. The corrosion attack on the tube sheet was caused by crevice corrosion between the surface deposit (bacteria product) on the tube sheet surface and the substrate.…”

“…However, the corrosion occurred under the gasket; therefore, macro/micro-fouling was formed and attacked the tube sheet surface. According to Figure 10, the corrosion mechanism was crevice corrosion between the substrate and surface deposit that was enhanced by microbiologically induced corrosion (MIC) [39][40][41].…”

“…The tube-sheet overlay was also attacked by corrosion ( Figure 11 is an optical micrograph of the unplugged tube. Corrosion occurred o inner surface of the tube, and the austenite grains were attacked by crevice corr [39,40]. Corrosion also occurred on the tube sheet overlay.…”

“…However, the corrosion occurred under the gasket; therefore, macro/micro-fouling was formed and attacked the tube sheet surface. According to Figure10, the corrosion mechanism was crevice corrosion between the substrate and surface deposit that was enhanced by microbiologically induced corrosion (MIC)[39][40][41].Figure11is an optical micrograph of the unplugged tube. Corrosion occurred on the inner surface of the tube, and the austenite grains were attacked by crevice corrosion[39,40].…”