Understanding CO2 in NACE MR0175 and other corrosion standards. 2

[acrmnsm]

I am trying to understand why NACE MR0175 does not give any CO2 maximum concentrations or partial pressures? It seems to imply that CO2 alone is not a worry, although I don't think this is true. I cannot find C02 limits in ISO 11960 or 13680 either.
So my question is - I think it is because they do give PH controls (typically = or greater than 4.5) and that CO2 corrosion is much worse below 4.5? So by keeping PH at or above 4.5 then the corrosion rate due to CO2 is minimised?
Please lead an ignorant man into the light ..

 

[SJones]

By "NACE" it is assumed that NACE MR0175 is meant. The key is in the title of the standards, where the word "cracking" is used. If you look at the discussion of CO₂ corrosion in API RP 571, you will note that it is not expected to lead to cracking although cracking is not unknown in some high strength steels with high CO₂ partial pressures - NACE Corrosion 2015, Paper 2015-6033.

MR0175 does not deal with metal loss corrosion caused by CO₂. For metal loss - pH relationships, you could play around with NORSOK M-506

https://www.standard.no/Global/PDF/Petroleum/M-506r2_IFE_06-2005.xls

or FREECORP

http://www.corrosioncenter.ohiou.edu/software/freecorp/

You are right in that the role of CO₂ in the standard is to drive pH as indicated in Part 2, Annex D

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.

 

[acrmnsm]

Thanks for this. So there is no standard that defines CO2 maximum concentrations for corrosion reduction?

 

[SJones]

@acrmnsm

No - because there will never be enough agreement to land on a unified approach to prediction, and then, there will be so many variables to juggle, including risk acceptance, that a single go - no go standard will never be possible.

Each to their own devices on a case by case basis for the foreseeable future.

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.

 

[acrmnsm]

Mr Jones you are a very nice and generous man, thanks for the posts.

 

[SJones]

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.

 

[Chumpes]

hi
NACE MR0175/ISO 15156 is only dedicated to the control of stress corrosion cracking(s) in wet H2S environments.
NACE MR0175 does not deal with generalized aqueous corrosion, temper embrittlement, atmospheric corrosion, polythionic acid stress corrosion cracking or any other degradation mechanism.
regards