Alloy 825 behavior under gas production environments

[rscosta1976]

Gentlemen,

Your thoughts would be appreciated regarding the pitting resistance of alloy 825 under the below service conditions for an gas producing inlet manifold, piping and slug catcher.

H2S: 3%mol
CO2: 5%mol
Temperature: 150 F
Pressure: 650 psig
Chloride content (of produced water): 150,000ppm
bicarbonate content (of produced water): 50ppm
Heavy sludge and halite salts are expected

As per NACE/MR0175 / ISO 15156, there are no concerns with SSC, however, I was wondering if there are any significant risk of pitting or under-deposit corrosion, given the low PREN of the alloy and that chloride content is above 150,000ppm and significant amount of deposit and (mainly halite salts) and sludge is expected.

I have seen other threads namely Link with interesting info regarding cracking risks. I haven’t found many literature references for pitting and under-deposit risk.

Thank you

 

[EdStainless]

With that much Cl and the low pH (from the CO2) you will pit 825 quickly.

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P.E. Metallurgy, consulting work welcomed

 

[SJones]

Have tested 825 in far worse conditions of all corrodents. No pitting. No cracking. It’s welds that need attention. Other associated testing resulted in setting a threshold of requiring a minimum Cr content of 39 mass%. You will note from the materials datasheets in IOGP S-563 that a minimum PREN of 32 is specified. A further recommendation would be to only use manufacturers with an ISO 17782 qualification that has been validated by an entity with acceptable metallurgical expertise. Very often, manufacturers will present just the front sheet of a NORSOK M-650 QTR that has been signed by some individual that, when further investigated, turn out to be the salesperson of the stockist that purchased the material.

You will also need to note that ISO 15156-3 does not cover as deposited weld metal. If a 625 welding consumable is used that will be a double non-conformance with ISO 15156-3

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

825 will resist cracking well, but crevice corrosion will be another issue.

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P.E. Metallurgy, consulting work welcomed

 

[SJones]

What will be the plan for the slug catcher materials? Unless there are multiple vessels to manufacture, 825 clad plate will probably not be cost effective, and it will be a case of weld overlay cladding. Some will argue that overlay with 825 is fine, and easily done; others will advise the more usual 625 weld deposition.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[rscosta1976]

Thank you all for your kind responses. I do apologize for my late reply.

@SJones,
Were any of the alloy 825 corrosion tests results published in the literature (papers, journals, etc)? I have search the most common literature sources and I couldn't find anything relevant. Please let me know, as I would be keen to see more details about it.

Before seeing your response, I was somehow concerned regarding pitting, crevice corrosion and under-deposit corrosion resistance of alloy 825 for the conditions mentioned above, as mentioned by EdStainless.


Thank you

 

[rscosta1976]

Greeting,

After additional searching, I was able to find a few papers that shed some light on the pitting corrosion resistance of alloy 825 is gas producing environments in sour environments containing reasonable amount of CO2 and also high chloride content in the produced water.

Rincon Flores, P.; Gonuguntla, M.; Khoo, C.A.; Behlani N.; Hajri. Z.; Al-Kendi, A. - “Design Challenges for Material Selection in Sour and High Salinity Gas and Oil Production Facilities”, Corrosion 2017, 9244

Kopliku, Ardjan; Cavassi, Paolo - "SELECTION OF UNS N08825 AS CLADDING MATERIAL FOR OFFSHORE PIPELINES TRANSPORTING SOUR MULTIPHASE HYDROCARBON", Corrosion 2002, 02042

The papers above refer to the risk of pitting, which have been confirmed by some lab tests. These have confirmed pitting risk of alloy 825 under conditions similar to the ones stated in this thread.
Following up on Sjones initial response, it seems the best path-forward would be to stick with Alloy 825 clad piping for slug catcher inlet circuits, provided this alloy with has a PREN above 32 and that some alloys elements are above specific threshold values. I would say, the minimum Ni should be set to 42% and Mo near the maximum of 3.5%. It seems clear that alloy 825 pitting resistance cannot be ensure in case the alloying elements are on the lower range allowed by the respective ASTM specifications, which may entail a PREN of 27 or 28.

Any additional thoughts and experience on this regard would be very much welcomed.

Thank you

 

[SJones]

The first paper is by my former colleagues, however, I organised a test programme in 2007 for a heavy sour project with 169,00 ppm chloride. Barely a blemish on numerous four point bend tests. Unfortunately, I can’t release the test reports. The facilities constructed with ‘basic’ 825 have provided satisfactory performance in the same environment since around 2009.

For a piping system, you may find that weld overlay 625 works out cheaper than trying to obtain hot roll bonded 825 to manufacture pipe.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[rscosta1976]

Thank you for sharing your experience and insights on this matter Steve.

We are considering to go ahead with some lab tests as well. The expected Cl content of produced water is around 220,000ppm and significant quantities of heavy sludge, constituted by sand and halite scale deposits in various proportions (depending on the field), are expected in a near future, as unconventional gas producing wells will be tied-in to existing gas processing facilities.

We will definitely consider 625 WO vs. 825 Clad option for the inlet piping in regard to price for the upcoming revamp project of the facilities.

Regards

 

[SJones]

Ah - you have changed the rules slightly: the OP was 150,000 ppm Cl-. Looks like erosion might be a further concern. You may need to examine the thickness of cladding required too.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[rscosta1976]

Yes. Sorry Steve,

The project team is still sorting out all operating cases for the next 15 years. We are still in an early stage of the revamp project.

Thank you very much for all your insights.