Pitting/ClSCC on 304/304L or 316/316L 5

[CoCoE]

Hello,

I really need some advise on this matter. In my knowledge chloride SCC, or pitting will not be caused by chlorides on Austenitic (considered here are SS 304 and SS316) stainless steels (ASS), if no oxygen or H2S is present and pH is around neutral. The presence of CO2 also will not promote Chloride SCC in these materials.

But my doubts are,

1. Is my above concept absolutely correct?
2. What is the impact of oxidizing agents on Chloride SCC/Pitting on the above ASS?
3. Will CO2 work as an oxidizing agent on SS?
4. I have gone through ASM Specialty handbooks, ASM corrosion handbooks (several), and many NACE papers. But I could not find any document stating confidently that "no limitation of chloride if no oxygen or H2S". Could anyone suggest a good reference?

Could someone please help me out?

Cococa

 

[EdStainless]

1. No
2. oxidizers will push the resistance up, but only so far
3. No, CO2 will push the pH down
4. The problem is 'no oxygen', you need a lot of chemical reducing agents to do that. Like lots of H2S so something similar, but often that leads to lower pH and higher risk.
Unless you are in a deep well or special chemical process reaching low enough oxygen to help suppress SCC is not realistic.

IF you have Cl SCC is a real risk. The lower the pH, higher the temp, higher the stress, the worse the risks.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

You forgot to mention temperature.

If temperature is below 40 C, the answer to the OP's first question is probably yes.

If temperature is above 60 C, EdStainless's concerns kick in.

Of course this all also depends also on HOW MUCH chloride too. Traces of chloride, or seawater? In a circumstance where concentration of the chloride in crevices etc. is possible, or not?

 

[CoCoE]

Hello,

The temperature is exactly 60, and some equipments are 63, and 65 deg C. Sorry for missing those.

pH is around 4.7 to 5

Produced water is from deep well, and no oxygen is confirmed. Chlorides are almost 10-12%.

So, do you mean even though no oxygen Cl SCC or pitting can occur in the above pH and Cl- concentration, an in presence of CO2?

Please advise.

CocoE

 

[moltenmetal]

By "no oxygen", do you mean that the oxygen level is parts per billion? If so, how was that measurement made? And what happens the first time you break into that line to do any maintenance work on it? A little of this water on the outside of this pipe would put the pipe at severe risk of ClSCC.

On the interior, the big worry is whether there is something else in that water which can take oxygen's role in the pit initiation process. If there is, the material is at risk.

It seems to me that using austenitic stainless steels in a hot brine with over 10% chloride is very risky. I'd want to see evidence that others have gotten away with using austenitics safely in such a service.

 

[EdStainless]

Is there any S at all? If so then the absence of oxygen doesn't matter.
You need to start looking at duplex SS grades as a starter, they at least have useful SCC resistance.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

Agreed- if this is a brine, S is likely present and you're probably going to need a duplex.

 

[Bain89]

Removing oxygen from the system will lower the stainless steel's open circuit potential, which will increase the distance from the OCP to the pitting potential.

 

[CoCoE]

@Edstanless and @Moltenmetal,

Thanks a lot for the inputs. This is from deep well, and it does not contain any oxygen or sulphur. (ppb value of oxygen is unknown), so 'no oxygen' is design consideration. If I select DSS, I am worried about the PWHT of DSS clad, and if solid, it is expensive. Any advise on this will be very useful.

@Rob89, I considered the same. Thanks a lot for your advise.

Thank you so much all, I am looking forward to your advise.

CocoE

 

[EdStainless]

Have you done the design in solid DSS?
Are these produced water lines or injection?
If produced is there any processing ?(separation or treatment)

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

Can we get a little clearer here:

1.
If it is 'produced water' what, exactly, is it being produced with?

2.
Are you selecting the well completion materials, or the transport system materials? If the latter, is it surface laid, or buried, and what are the well completeion materials being used to bring it to surface?

3.
What is the design pressure of the system, because you could be in a good spot for using GRP

4.
What items would need PWHT, and why?

5.
Why are CRA materials being touted as the first choice - what rules out carbon steel?

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.

 

[CoCoE]

Hello,

Sorry for replying late.

@Edstainless, 1) Selection is not yet done. DSS is under consideration, but I can't use a clad vessel due to code PWHT.
2) This is for inlet separator and colescers where the similar fluid is passing.

@SJones, 1)It contains CO2, and chlorides only. No oxygen and no sulphur. Could you please advise me what is the impact of elemental sulfur on austenitic SS?
2)Selection is for inlet separators and coalescers.
3) Pressure is approx 35 barA
4)PWHT is code requirement
5)Corrosion rate estimated is above 7 mm.

Regards
CocoE

 

[SJones]

If a separator is required, what is being separated from the water - gas? How was the corrosion rate determined for a pressure vessel? Why is PWHT a showstopper - so long as it is carefully done, and the correct quality control testing is passed, it shouldn't be an issue?

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.

 

[Bain89]

What chloride content are you exposed to? From experience 316Ti in 13,000ppm chloride and no oxygen there was no problem with pitting. The addition of oxygen to the system caused several pitting failures at welds. Pickling the weld with 6% HF solved this problem.

Rob Muggleton
Corrosion, Oil & Gas

 

[CoCoE]

@Sjones, Sorry again for being late.
What is separated? Gas
How was the corrosion rate determined for a pressure vessel? using E.C.E
Why is PWHT a showstopper? We experience a lot of worst cases.

@Rob89, 12% Chlorides.

Regards
Coco

 

[SJones]

With no H2S and no oxygen, take a look at Figure 4 in this document, noting that the environment is expressed as NaCl and needs adjustment for just Cl-:

https://www.nickelinstitute.org/Tec...istantAlloysintheOilandGasIndustry_10073.aspx

"We experience a lot of worst cases" requires more elaboration for understanding.

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.

 

[Fundy]

Worst cases, marginal applications, low oxygen, neutral pH, low temperatures .... there is no absolute data for calculating when Cl SCC is or is not an issue. However, in the Risk-Based world, there is a tool for assessing the likelihood of austenitic stainless steels (classically the "300 series") cracking in chloride-containing environments. Closely read the article "A New Risk Assessment Tool for Determining the Likelihood of Chloride Promoted Stress Corrosion Cracking in Austenitic Stainless Steels" <

https://inspectioneering.com/journa...t-tool-for-determining-the-likelihood-of-chl>

 

[moltenmetal]

Regrettably your link is dead.

 

[CoCoE]

Duplex clad is finally selected.

CocoE

 

[CoCoE]

Sorry, TYPO! Solid duplex is finally selected.

CocoE