LOCALISED CORROSION SUSCEPTIBILITY OF AISI 304L (UNS S30403) STAINLESS STEEL WELDED JOINTS IN SEA WATER

Summary

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 Cr23C6 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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