selective attack on duplex 1

[nabilou77]

Dear All,
anyone faced selective attack on duplex 2205 in carbonic acid solution at temperature around 70 Celsius degree. thank you for your interaction.

 

[EdStainless]

What kind of attack?
Pitting?
Is it related to welds, or phase boundaries, or preferential attack of one of the phases?

What concentration of acid?
Any scale of surface deposits?
What about impurities, such as metal ions or halides?


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[nabilou77]

it is preferential attack (most probably ferrite) with carbonaceous iron oxide as corrosion product (analyzed by EDX). no welds involvment.
Frankly, we do not have data on the acid concentration since it was a phenomenon in vapour space of MED process. regarding impurities, i will come to you later. Thanks

 

[EdStainless]

You need to do enough micro work to verify if the attack is at the phase interface or in fact in the ferrite.

Then you need to do some corrosion testing to see if they material was really heat treated properly.
Do G48C testing on freshly ground samples, increase the temp with each test until you just start to get attack, then look to see where it is happening.
Then do some very good micros, you would be looking for very fine precipitates, very hard to see.
Unless you have Br, Cl, Fl present 2205 should work well in this acid.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[nabilou77]

Thank you.
Indeed i already suggested to go for the micro scale to confirm the exact location of the selective attack.