Hi there
As a corrosion engineer, it was so interesting for me to compare SCC (Stress Corrosion Cracking) and SSC (Sulfide Stress Cracking).
One of the most characteristic differences between these two cracking mechanism is their mechanism from electrochemical conceptual point of view, so that one of them follows cathodic cracking mechanism and the other follows anodic cracking mechanism. In SCC mechanism, there is always an anodic reaction in which the surface of the metal corrodes at a weak point and corroded point or area plays an anodic area compared to the other surface area, and combination of the corrosion and stress concentration in corroded area ends in a rapid cracking phenomenon. While in SSC damage mechanism, it is a cathodic cracking mechanism which initiates this cracking phenomenon. Would you exactly explain:
1- What would happen in SSC mechanism ?
And
2- What conditions need to be present in wet H2S containing acidic solutions with pH of less than 4 to experience SSC phenomenon ?
Dear @Hadi Ghesmati Kucheki
Thanks for answering my question and contributing to this attractive topic.
I saw your valuable paper and i appreciate your work.
Now, let me ask you a conceptual question: we know that pH of the aqueous phase in oil and gas transporting pipelines is approximately 4 due to the presence of acid gases like H2S and CO2.
And from graph of acid gases dissociation versus pH we know that in low pH values of 7, H2S cannot be solved in aqueous phase and dissociate to HS- or H+ ions and more than 99% of hydrogen sulphide will be remain in gas phase and the remained part will be as unsolved H2S in the aqueous phase, as well. So, there would be no hydrogen ion to take up electrons from the pipe surface and promote cathodic reaction. It means that in low pH’s (in oil and gas pipelines fir example in pipelines of South Pats Gas field) there is no therest for SSC happening in the presence of H2S because H2S will remain unsolved in aqueous phase. I would like to get the answer to this question that why we assess SSC and HIC susceptibility in pipelines in which pH of the fluid is about 4???
Dear @Hadi Ghesmati Kucheki
Thanks for answering my question and contributing to this attractive topic.
I saw your valuable paper and i appreciate your work.
Now, let me ask you a conceptual question: we know that pH of the aqueous phase in oil and gas transporting pipelines is approximately 4 due to the presence of acid gases like H2S and CO2.
And from graph of acid gases dissociation versus pH we know that in low pH values of 7, H2S cannot be solved in aqueous phase and dissociate to HS- or H+ ions and more than 99% of hydrogen sulphide will be remain in gas phase and the remained part will be as unsolved H2S in the aqueous phase, as well. So, there would be no hydrogen ion to take up electrons from the pipe surface and promote cathodic reaction. It means that in low pH’s (in oil and gas pipelines fir example in pipelines of South Pats Gas field) there is no therest for SSC happening in the presence of H2S because H2S will remain unsolved in aqueous phase. I would like to get the answer to this question that why we assess SSC and HIC susceptibility in pipelines in which pH of the fluid is about 4???
Dear Askar,
As we know SCC is a high chloride content and SSC is a hydrogen embrittlement cathodic charging in the presence of sulfide. SSC is generally limited to steels. Unlike SCC, there is no requirement for a corrosion pit to serve as an initiator; crack can be initiated withing the bulk metal itself and propagating crack need to be connected to the exterior surface. In SCC, a pit could possibly present a stress-riser of sufficient magnitude to initiate a crack.
Ashish
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