Electrochemical Impedance Analysis on Cryogenically Treated Dissimilar Metal Welding of 316L Stainless Steel and Monel 400 Alloy Using GTAW

An attempt was made to study the corrosion behavior of austenitic stainless-steel SS 316L/Monel 400 alloy dissimilar metal welded joints using gas tungsten arc welding. This combination of welded joints is used in re-heaters and heat exchangers in gas processing and oil refining industries. The welded specimens were subjected to post-weld treatments, such as annealing and deep cryogenic treatment. The welded specimens were sectioned into five different parts: SS 316L base, SS 316L HAZ, weld, Monel HAZ, and Monel base. The polarization method and electrochemical impedance analysis were used to analyze the corrosion resistance in a NaCl solution. A polarization graph, Nyquist plot, and Bode plot were constructed for all regions, separately, for the heat-treated and cryo-treated specimens, to analyze the variation in corrosion resistance in different regions, and then the results were compared. To validate the results of electrochemical impedance analysis, scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) analyses were also performed. The results indicated that the cryo-treated specimens have better corrosion resistance when compared to the annealed ones. Weld region on both specimens exhibited better corrosion resistance when compared to other zones.