2 replies to this topic

[ethanhan]

To dear all experts


I would like to know the clear defintion of H2S corrosion. Does it occur when there is dry, without aqeous solution? Does other Hydrogen attack occur when there is dry? Finally , please recommend some good book or referrence.

Regards
Ethan

[Root]

Hi,
1

[/indent]H2S have corrosion tendency, more when moisture is present but some process being using the H2S as passivation to avoid from H2 corrosion attack.
2
[indent=1]

H2 Has more tendency for corrosion for CS, SS347 on high temp applications, therefore H2S or DmDS is being used for the protection of H2 corrosion attack.
if you want more detail read UOP manual for Reformars of petrochemicals.
Hope this will help you.

Cheers

[JoeWong]

H2S dissolved in water to form weak acid promote corrosion and free hydrogen. Free Hydrogen will penetrate the metal, reduce ductility of metal and potentially lead to stress failure below it yield stress, results Sulphide Stress corrosion cracking (SSCC). Dry H2S may not cause SSCC.

Apart from SSCC, H2S also cause other cracking, including stress corrosion cracking, hydrogen-induced cracking and stepwise cracking, stress-oriented hydrogen induced cracking, soft zone cracking and galvanically induced hydrogen stress cracking.

Hydrogen gas could lead to Hydrogen embrittlement. Thus it can occur in dry environment. H2 embrittlement is the embrittlement of metal or alloy involves hydrogen ingression in to metal or alloys matrix and significantly decrease it’s ductility (ability to deform), cause metal or alloys crack and catastrophic failure at stresses below normal yield stress level of the attacked material. Read more in "Hydrogen present and it's impact to metallurgy".

At elevated temperature, High Temperature Hydrogen Attack (HTHA) will also occur. High Temperature Hydrogen Attack (HTHA) is a form of degradation caused by hydrogen reacting with carbon to form methane in a high temperature environment.

C + 4H --> CH4

The methane forms and stays in grain boundaries and voids however it does not diffuse out of the metal. Once it accumulated in the grains and voids, it expands and forms blister , weaken the metal strength and initiate cracks in the steel. Read more in "High Temperature Hydrogen Attack in metal & alloy"

NACE MR 0175 - ISO 15156 -2005 is a good source of H2S related corrosion.