Stainless steel for produced oil and water. 2

[Saad M.M.]

I am researching about the stainless steel limits in produced oil and water environments. I found a little in the literature about stainless steel corrosion and limits in oxygen free environment (pitting and crevice corrosion). Most of the limits I found in the literature including, SCC temperature, CPT and CCT including ASTM G48 procedures assumes aerated testing medium conditions.

On the other hand, producers experience indicate successful use of 316 SS in wet oil and producing water environments with no records of failures for decades. The chlorides level in these environment can be very high (in excess of 30,000 or 40,000 ppm) and operating at temperature that can reach or exceed 60 C/ 140 F. Furthermore, NACE MR0175 sets very high limits to 316 SS material (up to 50,000 ppm of chlorides at 90 C, in mild H2S environment). Furthermore, a well-recognized publication by Craig and Smith point to high limits of chlorides and temperature based lab research and operators experiences. The problem becomes more complex with consideration to pH, CO2 and H2S.

Can someone help me and point out what I am missing. Is there a reference (from internationally recognized organization) that discuss the SCC, CPT and CCT limits for stainless steels in oxygen free environment ?

 

[SJones]

What do you think that you are missing? The research data shows you the limits that have been established by laboratory testing and operating experience for environments on the inside of the system. Very often, it's considerations of the environment on the outside, or that will probably exist during installation and pre-commissioning, that become dominant. Your research should also include NORSOK M-001/ISO 21457, and, given your stated discipline, a large number of NACE corrosion conference papers on the NACE Bookstore site. The Craig & Smith graph is in the absence of H2S don't forget, so the ISO 15156-3 limits indicate the impact of adding H2S into the exposure environment. The simple approach is: make sure operations won't do anything to let air into the system whilst in service.

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.

 

[Saad M.M.]

Thank you SJones for your feedback.

When it comes to new project design and material selection, the designer is liable to provide the necessary material performance guarantees. Unfortunately, conference papers may not always be based on reliable testing conditions or test may not re-producible. And company experience may not always be compatible with the new project conditions. I personally have very strict rules about accepting any data point for material selection use.

For example, a case of high temperature (90 C), high chloride (110,000 ppm), non-sour production system at a pH >> 5. If this was a sour system, this will be easy as per NACE MR0175, and it will take me immediately to nickel alloys 825 or 625. However, for non-sour I got lost with the CRA options. Can I just use Craig and Smith diagrams? or is there a commonly recognized standard that I should refer to? please note that this example is real and it is not addressed by NORSOK M-001/ISO 21457 or even EEMUA 194.

What makes this more challenging is the way CPT and CCT data are presented which can be misleading and can result in end-user misunderstanding and objections. It is very frequent that standard or paper authors ignore the fact that SCC, CPT and CCT tests were done in aerated aqueous conditions, and results will be different in oxygen-free environment. For some reasons, I couldn't find SCC, CPT or CCT data for oxygen-free environments.

 

[EdStainless]

It is a risk management question.
You know full well that at pH6, and 60C you can expect rapid pitting of 306L at 200ppm Cl. So where do you strike the balance?
In systems that always have some flow and a low water fraction the surfaces may always be wetted with oil and you can get away with some amazing things.
In sour systems it is nice, because the oxygen is zero, until you get above ground. If you are above ground you have to assume the worst case oxygen levels. If it is above ground you will never have zero oxygen.
Why don't you look at some ref like these:

https://nickelinstitute.org/media/1649/controlofcorrosioninoilandgasproductiontubing_14052_.pdf

https://nickelinstitute.org/media/1...rdesalinationandoilfieldbrinepumps_11004_.pdf

and dozens of other similar ones.
One problem is that the documents that you are referring to offer no guidance on avoiding pitting and crevice corrosion. they are trying to prevent catastrophic (CSCC) failure.

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P.E. Metallurgy, consulting work welcomed

 

[Saad M.M.]

Thank you SJones and EdStainless. Very useful feedback.

 

[SJones]

No problem. If you search you will find plenty of pitting and crevice studies in simulated oil & gas service conditions. Ed's statement regarding data being solely for cracking mechanisms is true to some extent, especially for materials that have been grandfathered into ISO 15156. However, there is a tacit expectation that balloted materials would have had a pitting evaluation of the qualification test pieces since pitting is a recognised precursor of cracking. Certainly, when some operators evaluate performance limits, pitting evaluation is most definitely an additional acceptance criterion of the SCC/SSC test.

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.

 

[Bibek29]

In oil & gas applications, inside the system, corrosion effect is considered to be less than that of existing outside viz. considerations of the environment, in contact with air. In view of that, various tables in ANSI/NACE MR0175/ISO 15156-3:2015(E) shall be referred, for the queried material. No data submitted (NDS) points shall be co-related with various material test results only; the same may NOT be available in ANSI/NACE MR0175/ISO 15156.
Regards,
Bibek.