Effect of microstructure on crevice corrosion for SDSS

[awesomeness]

Hi,

We have a case where we have experienced crevice corrosion on SDSS flanges made from forged material but not for those made from plate, in the same environment. Both are UNS S32750. The environment is chlorinated seawater (dosing ranging from 0,2 to 0,7 ppm) and a seawater temperature ranging from 5 to 15 degC. Both are situated in the splash zone. No painting, no cathodic protection.

We were not expecting any corrosion issues with this material in this environment, but have experienced two issues with the forged flanges lately. Two different, but similar locations, and forgings from two different manufacturers.

Can differences in microstructure from forged to plate affect the crevice temperature?
Can for instance a finer austenite spacing make a difference?

Thank you

 

[Dhurjati Sen]

Send a sample of the affected flanges to a laboratory for chemical analysis (and not a PMI test) to check if these really conform to S32750.

 

[EdStainless]

Did you require the forgings to be tested to A923 B or C?
If not then they may not have been annealed and quenched properly.
If there are any intermetallic phases they will have a pitting resistance far lower than expected.
They will also have lower mechanical toughness.