Material Selection For Corrosive And High Chlorides Fluid 8

[Noman409]

Hi,

I am currently working on a gas processing plant offer in which the maximum CO2 content in the raw gas shall be taken at 25 mole% and 15 PPM of H2S. The chloride level in water is up to 14,500 mg/L. Operating temperature of the fluid is 250 F and operating pressure is 1186 psig. Client has asked to select appropriate / suitable CRA (corrosion Resistant Alloy) metallurgy of material. Can anyone help me in the selection of MOC based on the above mentioned conditions of fluid? Please note that at downstream there is an evaporative cooler which will lead down the temperature up to 135 F. Please guide me regarding the MOC for upstream and downstream of that evaporative cooler. Can i go with SS 316 on theses fluid conditions?

Regards

 

[EdStainless]

You could measure time to failure of 316 in this application with a stop watch.
So, you will have a pH of about 3, 15,000 ppm Cl and 250F.
You could use alloys like 4565, AL-6XN, 654SMO, and they will be borderline.
That leaves you with a "C" type Ni alloy (C22, 686, 59) or Ti (but not CP, it will need to be an alloyed grade such as 12 or 16).


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P.E. Metallurgy, Plymouth Tube

 

[XL83NL]

Er, do you have any literature or reference that one can use as a first guideline on these kind of matters, just to get a hint at a possible CRA for such environments (I.e. acids, chloriden,etc.)?
Ive been asked such questions every now and then, but have always forwarded them to experts. The subject itself however is interesting to have some basic understanding about.

 

[EdStainless]

Start here

http://www.outokumpu.com/en/tools-and-downloads/tools/Pages/default.aspx

And look at their corrosion guide. If you request a print version it has bunch of support information in it.
There are also many good papers at

http://www.nickelinstitute.org/

look in the Knowledge base

Good luck, Ed

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

For the case in question, this document would probably make a good start:

http://www.nickelinstitute.org/Tech...istantAlloysintheOilandGasIndustry_10073.aspx

Since there is H2S around, ISO 15156-3 will also apply which will also give application limits of materials in terms of the key variables: temperature; partial pressure of H2S; chloride ion concentration; pH. You might like to work with design pressure to calculate the partial pressure of H2S (Note: design pressure is the process design pressure and not the maximum rated pressure of the class).

From these two documents, you might identify 22Cr duplex stainless steel as a candidate.



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.

 

[Noman409]

Thanks guys for your help. I believe 22Cr duplex stainless steel would be the best option for this fluid condition.

 

[EdStainless]

You can believe that, but if you have any crevices or any fouling you will find differently.
The Cl level is not a very big factor, but pH=3 and 250F are what will drive this.
Take another look.

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P.E. Metallurgy, Plymouth Tube

 

[CoCoE]

Can you please clarify Er Ed, how did you estimate the pH as 3? Only by pressure? How about the impact of 25 mol% impact of Co2 concentration?

Regards

Krishn

 

[EdStainless]

With enough CO2 and pressure (you have a partial pressure of 400psi) the pH will tend toward 3, so that is often used as worse case for CO2 systems. Though the high temp will make it not quite that bad.

If you look at the curves carefully you will notice that the duplex alloys suffer far more impact from the presence of H2S than the austenitic alloys do.

I cannot imagine trying this with a 22Cr duplex.

I wouldn't try with anything less than a Ni-Cr-Mo "C" alloy, unless the cost of failure is very low.
Once you reduce the temperatures alloys such as 2205 or 825 become very good candidates.



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P.E. Metallurgy, Plymouth Tube

 

[CoCoE]

I am sorry, Er. Ed, I am just a starter, and would like to know how you got the pH as 3 and partial pressure as 400 psi, referring to which curve?

As per dalton's equation, the partial pressure will come around 296 only as per the current operatin pressure. Also the design pressure is not given.

Can you please explain? I would like to know from you. Please help.

 

[EdStainless]

If the op press is 1200psi then design must be somewhere above that, and 25% fraction sound a bit like wishful thinking, so just padding a bit.
And based on curves and experience I know that in room temp high pressure systems carbonic acid will reach pH of 3.
The exact value does not matter. It will be less than 5 for sure, so you need to assume that condition can be worse (because they always will be).

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

The table in ISO 15156-3 indicates 22Cr DSS to be tolerant of 232 deg C and 10 mbar a of H2S with no restrictions on chloride and pH. To derive the temperature and H2S limits testing must have been performed. It is not clear under what conditions. The Nickel Institute document shows, again by test data, that 22Cr has substantial resistance to CO2 and chloride at temperatures far higher than 250 deg F. Currently, I am working with operator standards offering 200 deg C, 10 mbar a H2S and 150,000 ppm chloride derived from a substantial bank of test data including pH values developed with large amounts of CO2. The testing has included crevice corrosion testing. The OP has not given the full water chemistry, but given the chloride content it is likely to be formation water that will contain other ions to push up the pH. If there is any issue it will be with welds, and welding procedure qualifications should include simulated service corrosion testing if there is an intolerable risk associated with failure.

Thus 22Cr could be a candidate material, but as the Nickel Institute document states, "The reader is advised to consult the latest test data and ISO 15156 corrigenda or make an evaluation based on testing for the specific application."

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.

 

[Bandar85]

You have quite interesting combination in your stream, Carbon dioxide can form carbonic acid leading to carbon dioxide corrosion and also result in a significant reduction in the pH . CO2 Corrosion can be very aggressive because of low pH conditions. existing of sufficient quantities of(H2S) can decrease the CO2 corrosion rate and could change the complete corrosion mechanism to fully sour H2S corrosion. So. if we consider that H2S will be monitored at the percentage given in your question and won’t reach to very aggressive level. Then, only Carbonic acid scenario will be taken in consideration. In that case, Doblex SS can be suitable to be used but duplex stainless steels ≤ 25% Cr are not recommended for use in acid condensing situations due to corrosion considerations. Moreover, new issue will appear which is the presence of high Cl.
ClSCC can be occurred and the factors which influence the onset of cracking are concentration of chloride, temperature, stress level, solution & pH. Duplex stainless steels are not immune to ClSCC but show an increased resistance to cracking. H2S has a synergistic effect with chloride on ClSCC of duplex SSs.
Higher nickel alloys such as the “superaustenitic” grades and Inconels/Incoloys and alloys approximately >45% Ni (Hastelloys, Monel) are preferable to be used in your case. If there is cost restraint you can think about cs pipe with an internal alloys cladding.

You should also ask your client to concern about the cooler's material if condensation will take place there.