LOCALISED CORROSION SUSCEPTIBILITY OF AISI 304L (UNS S30403) STAINLESS STEEL WELDED JOINTS IN SEA WATER
Publication Date : 31/01/2017
This study is on the susceptibility of AISI 304L austenitic stainless steel welded joints to localized pitting corrosion in sea water. AISI 304L is more resistant to corrosion primarily because of its low carbon content. This makes it less susceptible to welding sensitization. However, high power density welding techniques like electron beam or laser beam creates a narrow HAZ and with its rapid cooling leaves the Cr in solution for formation of Cr-oxide. The study compared the pitting resistance of welded joints [produced by SMAW and MIG] in two sea waters –one natural (of 4% dissolved salt content) and the other synthetic (of 8% dissolved salt content). All the studies were by immersion method. The WM and HAZ by MIG indicated higher pitting corrosion resistance in both environments, that of SMAW were found susceptible in both media, with higher pitting density in the greater salt-concentration environment. The near-high power density of MIG process succeeded in creating a narrow HAZ because of sharp thermal slope inherent in the technique. This was not the case for SMAW joints with extended HAZ and attendant Cr 23 C 6 precipitation / Cr depletion. From this paper, AISI 304L welded joints made by MIG and service-deployed in sea water (dissolved salt content < 8%) handling facilities can be considered stable and “safe.” The SMAW process sensitized the HAZ, and the regions of austenite / delta-ferrite interface was greater -hence the corresponding corrosion-weak sites. This negatively shifted the pitting potential of joints by SMAW.
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