CO2 corrosion 1

[rotw]

Hello,

We know that the a gas is corrosive due to CO2 when there is presence of CO2 and water.
However the corrosion occur when water is in the liquid phase.

My question is what about presence of CO2 in a heavy hydrocarbon condensate (without any water content).
Sorry if my question is not smart but I would like to know this lead to corrosion of carbon steel in particual especially if the partial pressure of CO2 is relatively high ?

Thank you

 

[zdas04]

CO2 corrosion comes in two flavors--Mesa Attack, and Acid Attack. Mesa Attack requires a very narrow pH range (around 5.5-6.5) and Acid Attack happens at a lower pH (less than about 3.0). Both are anodic reactions. They require an anode, an electrolyte, and the acid acts as the cathode. There are two important questions: (1) when your hydrocarbon liquid absorbs CO2 is there an chemical reaction that leads to an acidic fluid? and (2) Will the resulting fluid conduct electricity? The second question is not a slam dunk--many hydrocarbon liquids are conductors, but others are insulators. The first question requires knowledge of your fluids that you didn't provide. I don't know of a CO2-gas/hydrocarbon-liquid reaction that results in an acidic compound, but that just means I don't know of one.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[rotw]

zdas04,

Your answer is very clear. Thank you as it help me to understand a little bit better why we generally characterize wet CO2 corrosion condition from the point of view of relative humidity (typically above 60%) and partial pressure criteria. So to say we are interested in the possibility of having water in liquid phase combined with certain amount of CO2.

The question is general and comes out from dealing often with natural gas containing heavy HC (say C6 and above) where some condensation might occur and be carried over in the main gas stream basically due to poor provisional margin to dew point (compression applications).
When a certain amount of CO2 is known to be present, I was wondering why typically this situation does trigger concern in the technical community with regard to the risk of corrosion. Behind my question is the objective to ensure that the material selection remains appropriate.

So I understand the phenomenon is not something really encountered or deserverving much of attention when it comes to wide spectrum of applications typical in the natural gas/hydrocarbon industry althought it is theroretically possible.

 

[rotw]

I was wondering why typically this situation does trigger concern in the technical community

I meant:

I was wondering why typically this situation does not trigger concern in the technical community

 

[SJones]

So I understand the phenomenon is not something really encountered or deserverving much of attention when it comes to wide spectrum of applications typical in the natural gas/hydrocarbon industry althought it is theroretically possible.

Not quite. CO2 corrosion is up there with atmospheric corrosion as one of the most common oil and gas production degradation mechanisms. Don't confuse hydrocarbon condensation with water condensation. You will need an aqueous phase for CO2 corrosion and the issue becomes one of how lucky do you feel with regard to the presence, or not, of water. One rule of thumb that some corrosion engineers work with is: CO2 corrosion risk is low if the operating temperature of the equipment remains a minimum of 10 degrees C above the water dew point of the fluid. What happens when it isn't, and how do you monitor for it?

If you feel inclined, try playing around with this model - it will give you numbers to help visualise the potential carbon steel metal loss:

http://www.standard.no/en/Sectors/Petroleum/NORSOK-Standard-Categories/M-Material/M-5061/

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[rotw]

Sjones.

Thanks for your valuable message but I did not get very well your reaction with respect to the quote.
The reason is CO2 corrosion in presence of water is not the point of focus.
I mean I am particularly interested in this thread about interaction between CO2 and heavy HC in liquid phase trying to understand how this can lead to a corrosion phenomenon.
Zdas, has been also quite clear and indicated the two conditions necessary for this phenomenon to occur and I guess I catched from his message that it seems a rather theoretical situation.
Having said this your link to Norsok seems to treat about the CO2 corrosion in presence of water in liquid phase and is still an interesting subject, I am happy that you posted it. Thank you