(Help) Corrosion Rate on surface Casing

[cussons]

Does anybody know how to calculate corrosion rate on surface casing based on theoretical approach? or the software for calculating corrosion rate for CO2 and H2S environment?

thanks

 

[SJones]

There is no model that deals in an acceptable fashion with sour corrosion because the mechanisms are still not fully understood. Several models attempt it but all have some drawbacks.

Search on Electronic Corrosion Engineer by Intetech and FREECORP by Ohio University. The links are on Eng Tips somewhere.

Steve Jones
Materials & Corrosion Engineer

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

 

[strider6]

here you can find the link for Nosrok and Freecorp. Norsok software has a limit on H2S partial pressure.

http://www.corrosionist.com/Software_for_Corrosion_Prediction.htm

S

Corrosion Prevention & Corrosion Control

 

[SJones]

NORSOK doesn't deal with H2S at all!

Steve Jones
Materials & Corrosion Engineer

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

 

[strider6]

Steve

If you open the M506, rev 2 - year 2005,software in the first window is clearly written that the model is applicable up to a partial pressure of H2S = 0.5 bar.. or that is not applicable when the ratio of partial pressure of CO2/H2S is less than 20, what is called "sour corrosion"...
..so the model is applicable even with H2S...

regards

S.

Corrosion Prevention & Corrosion Control

 

[SJones]

Indeed, but look at the first paragraph on page 5 of the accompanying document:

The program covers only calculation of corrosion rates where CO2 is the corrosive agent. It does not include additional effects of other constituents that may influence the corrosivity, e.g., contaminations of O2, H2S etc

All NORSOK is doing with the H2S input is determining the effect on water pH and its implications for CO2 corrosion. It is not assessing the formation of protective sulphide films which would lower the corrosion rate for example. It is a CO2 model only and not a CO2-H2S model; not that there is currently any validated CO2-H2S model around but ECE 4 and FREECORP have a better go than NORSOK when there is H2S present.

Steve Jones
Materials & Corrosion Engineer

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

 

[strider6]

Steve
I agree with you that there is not a model that account for H2S, but when the ratio of CO2/H2S is above 20 the general recomendation is to consider the system as a "sweet corrosion", not taking into account the H2S. So in my opinion if the limit stated in the software are respected the model can be used.
If the ratio is below 20 than the system is considered as "sour corrosion" and the effect of H2S on CO2 corrosion is important.

S

Corrosion Prevention & Corrosion Control

 

[SJones]

the general recommendation is to consider the system as sweet corrosion

I don't think it's quite as clear cut as that and there are a number of factors to consider some of which could lead to accelerated corrosion whereas others could retard corrosion.

Anyway, the upshot is that if the thread originator uses any corrosion prediction model for an H2S containing system the results will have to be treated with caution. It is not an area for the inexperienced!

Steve Jones
Materials & Corrosion Engineer

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

 

[strider6]

Steve

You're right, this is an argument for people with experience in this field.

S

Corrosion Prevention & Corrosion Control