Duplex vs aust vs Inconel alloys in H2S 3

I do agree that your selection of material based on crystalline structure is inline with a cross section of corrosion data concerning H2S environments.

I have a problem with generalizations concerning the suitability of materials for a particular service. If a generalization statement is made it should be fully qualified as to specific environments or better yet exclude certain environments. People tend to make literal interpretations of such statements. I’ve certainly got burned several times.

What work with H2S that I’ve been involved in certainly wouldn’t have involved any general statement. I have found that H2S corrosion problems are in the same league as Amine corrosion problems, that is each particular environment requires a particular study and recommendation.

There are too many variables in materials recommendation to generalize other than say this is a very good starting point for study or survey.

Since the issue you're referencing is cracking in H2S, this order is correct because austenite stability is the key to resistance of austenitic structures. The presence of ferrite is a negative.
There are a lot more considerations, but the quotation stands as a valid one.

Thanks Unclesyd and Mcguire for your replies, a star to each of you.

Thanks and regards
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I think your list is true for the practical situation of service environments where the media in contact with the alloy is more complex than just H2S i.e. oil field process fluids also containing water, CO2 and chlorides.
In a situation of "simple" H2S exposure then fully ferritic/martensitic materials processed and controlled in accordance to NACE M 01 75 work fine.

If you use ferritic material, you must guard against cold-work, which renders a material which is okay in the annealed condition susceptible to cracking. This happens with alloys like 29-4C and Sea-cure when tubes are swaged into tube sheets. I don't know if the NACE spec addresses this.

Yes - the NACE MR 01 75 spec. puts definitive limits on the amount of cold work which is acceptable.

Guys, let me give you a different perspective from the oil&gas engineering industry. First no rules no generalization is a wise attitude when dealing with corrosion matters. Second you mix two different variables with different behaviours: microstructure and alloys.
The stress cracking is an outcome of the corrosion mechanism when hidrogen is the product. Concerning the last, the more Cr content the better (up to 12-13 %Cr, over that some detrimental effects on other sides need to be evaluated, regardless of the microstructure. That is because of the passivation effect of the anodic Cr in the steel. Less hidrogen hence less SC susceptibility.
But once you get hidrogen in the metalic net it combines to get hidrogen molecule with a huge volume expansion and that creates the internal stresses deriving in induced fragility of the metal. So you must care about how soft your steel is as to mitigate this effect. It is normally accepted that a rockwell hardness less than 22 is acceptable (NACE). You are closer to get this in ferritic-perlitic structure than you can be on martensitic structure. Which one do you want to prevail? Best economically is 13Cr ferritic but it is soft and delicate. More resistance?. Use 13Cr martensitic (super 13Cr)Do you want something in the middle, use austenitic structure, or better both: ferritic+austenitic (duplex)