Stainless steels are susceptible to crevice attack
in chloride bearing waters. Their behaviour has been
studied by a number of investigators. There is considerable
variation in the percentage of apparently identical
sites where attack occurs, when it occurs. It is useful
to describe results
in terms of the percentage of apparently identical sites
where attack occurs at a given chloride concentration.
Very tight stationary crevices increase the likelihood
of attack. Rough surfaces, sheared edges, scratches
and similar imperfections also tend to increase the
incidence of attack.
Crevice attack also occurs under deposits and under
biofouling growths attached to the surface.
The 4.5% Mo and duplex stainless steels are more resistant
than type UNS S31600,
but suffer varying degrees of crevice attack in brackish
water and seawater. The 6% Mo super-austenitic stainless
steels have excellent resistance to crevice attack in
seawater.
UNS-S
Chloride
concentration below which crevice attack
is rare
This table provides useful guidelines towards crevice
corrosion, however, it should be noted that chloride
concentration may be locally intensified within the
crevice.
