Wet H2S vs Sulfidation 3

[A.M.B.]

Dear all,

I have been trying to understand the exactly difference between this two damage mechanisms: sulfidation and wet H2S damage.

I was wondering; if sulfidation occurs mostly due to H2S and the main reaction is Fe⁺ + e^- + HS^- + H⁺ --> FeS + 2H
and this reaction is the same as the main reaction in wet H2S mechanism, why isn't a concern the atomic Hydrogen difussion in sulfidation conditions?

Thanks in advance.

 

[NBrink]

You form atomic hydrogen from high temperature sulfidation (and can estimate corrosion rates with a hydrogen flux meter), but at the higher temperatures that sulfidation corrosion is a concern, the diffusion rate is great enough you don't charge the steel. Just diffuses right on through. Kind of doing a "bake out" at the same time...

Nathan Brink

 

[EdStainless]

Exactly, sulfidation is a high temperature reaction so it is not aqueous.
Sulfidation will occur under either oxidizing or reducing conditions and is worse when combined with Na, Cl, P and other fuel impurities.

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P.E. Metallurgy, Plymouth Tube

 

[A.M.B.]

In first place,thanks for your answers.
I understand that because of the temperature you wont have aqueous phase.

NBrink said that at those temperatures hydrogen difussion rate is great enough yo don't charge the Steel.
But assuming you have a poor quality Steel with discontinuities such as laminations or inclusions, won't be blistering a concern?

If you have wet H2S, the difussion rate would be a direct indicator of the probability of that damage occur. Or am I wrong?

 

[EdStainless]

The hydrogen would only be an issue if there were inclusions that it reacted with.
At high temp hydrogen won't collect, it diffuses too easily.
Now if the back side of the steel is cold that is different, because at some depth the H wants to stop moving freely.

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P.E. Metallurgy, Plymouth Tube