Sour Water Injection Line? 1

[julieangel]

Hi,

I need some guidance in this matter! I received a water analysis for a water injection line operating at 700 psi, 50C. I need to determine if the fluid is sour and if it is compatible with 316L. The water contains:
CO2 Gas Analysis 18.12(%)
H2S Gas Analysis 0.2211(%)
Total H2Saq @ Standard Pressure and Temperature (STP) 7.09 (mgH2S/l)
pH (STP) 5.82
Cl- 125,930.73 (mg/l)

When trying to calculate partial pressures of H2S I am getting confused with H2S gas percent and Total H2S aqueous. Which one should I take into account? Both? Which one will drive the corrosion process? Any feedback will highly appreciate it!

Thanks.

 

[SJones]

On the assumption that you are using ISO 15156-3, try thinking of the following:

1. What is the minimum partial pressure of H2S required to class the fluid as sour (hint: if you can locate one, let us know)?
2. The environmental maximum limits for 316L are in Table A.2 (don't forget to use the latest table in Technical Circular 3

http://isotc.iso.org/livelink/livel...2014-01-27.pdf?func=doc.Fetch&nodeid=16436970

). Note that the H2S limits are expressed in terms of partial pressure.
3. How will you get a partial pressure from a liquid full system (hint: look at ISO 15156-2, C.2)
4. The corrosion process is driven by the H2S in the aqueous phase which is related by physical chemistry to the partial pressure in the gas phase
5. The validity of the quoted pH value when considering actual design conditions.
6. The quoted chloride content is already twice the allowable for S31603

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.

 

[julieangel]

Hi Steve,

Thanks for all your helpful tips and hints. This is very useful information. I am following MR0175/ISO15156 and according to the standard you just need as little as 0.05 psi partial pressure to be considered sour. I also noted that ISO 15156-3 has more information regarding 316L. Thanks again!

 

[SJones]

The belief regarding > 0.05 psi partial pressure of H2S is solely (and usually incorrectly) linked to carbon steel and does not apply to alloys in Part 3. Look at definition 3.19 in Part 1 and interpretations #2009-11, Parts 1 and 2 at

http://isotc.iso.org/livelink/livel...c=ll&objId=3340364&objAction=browse&sort=name

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.

 

[blacksmith37]

Possible corrosion problems of the 316 will be caused by Cl and possibly, MIC (bacteria).
In 15 years on the MR 01-75, we sure got tired of people trying to use it as a guide for weight loss corrosion (which it is not) . I guess the ISO people have made some changes.

 

[EdStainless]

H2S aside, you canno0t use 316 successfully at that pH and Cl level.
You will be moving to a higher alloy.

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Plymouth Tube

 

[julieangel]

We are considering duplex 2205 or super duplex for some parts of this line. I know MR0175 is not a guideline for corrosion control or other type of corrosion like pitting. I was following it for partial pressure calculations. I wasn't aware the 0.05 psi H2S limit only applies to carbon steels. Thank you all for your helpful comments!

 

[EdStainless]

If this is an injection line then you have been handling the water at the surface.
So it now probably contains oxygen.
It will much more aggressive than when you pumped it out of the ground.
At pressure with more CO2 dissolved the pH will be more like 3.5.
A 6% Mo super-austenitic or a super-duplex might stand a chance, but there is still significant risk with those alloys in this water.
Go back and read NACE papers on pitting limits of various alloys.

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Plymouth Tube

 

[SJones]

GRP followed by PE lined carbon steel would be my choices for a new build without knowledge of the particular design details.

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.