As previously noted, microbially induced intergranular
pitting and IGSCC can occur in sensitized
stainless steels, where low chromium
content at grain boundaries allows preferential
dissolution (Ref 41). However, it has been found
that transgranular pitting due to MIC in the heataffected
zone in socket-welded specimens of 304
stainless steel exposed to flowing lakewater (500
to 600 ppm chloride) over 6 to 18 months was
not focused in sensitized areas (Ref 74). Instead,
pitting occurred along deformation lines left by
cold working of the metal during manufacturing.
Annealing the material at 1150 C (2100 F) was
suggested as a way to remove these features and
increase resistance of the material to MIC. No
pitting was seen in the base metal for either
furnace-sensitized or girth-welded specimens of
304 or 316 stainless steel after similar exposure