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.

 

[awesomeness]

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.

Thank you for your reply.

The forgings are purchased in accordance with NORSOK M-630 MDS54, grade F53. No indications of intermetallics on micro performed in the material certificates.

But in general there should not be any difference in corrosion resistance between plate and forging, right?

 

[jessieleo99]

In theory, plate and forging shouldn’t behave differently if both meet specs.

Thank you for your reply.

The forgings are purchased in accordance with NORSOK M-630 MDS54, grade F53. No indications of intermetallics on micro performed in the material certificates.

But in general there should not be any difference in corrosion resistance between plate and forging, right?