AISI 316 FOR DOWNHOLE CASING MATERIAL 4

[GabrieleB]

I'm working for a Client that is going to install AISI 316 for a downhole casing material (on a production well).
The general condition is:

[ul]
[li]Temperature 55°C[/li]
[li]P H2S 50 Kpa[/li]
[li]150.000 mg/l of chlorides[/li]
[li]PH<4[/li]
[/ul]

Looking on ISO 15156-3 Table A.2 (applicable for any equipment or components) seems to be this choice acceptable, because for temperature below 60°C and P H2S <100 Kpa any combination of chlorides and PH can be accepted.
Moreover on ISO 15156-3 Table A.9 (specifically applicable for downhole tubular components), the same restriction above mentioned is given for a better alloy (superaustenitic SS).

My concern is that the table A.2 above mentioned cannot be used for downhole tubular components being this application more stringent for the material selection. Infact the ISO 15156-3 suggest superaustenitic alloy minimum for this application.

My opinion is that the AISI 316 used as a downhole casing equipment is not suitable for the purpose with a fluid of such composition (cause of chloride pitting and HIC risk) and I would suggest them to use a superaustenic alloy or in any case any alloy with a PREN > 40. Even though if the table A.2 can give them some misleading overview of the issue.

What is your suggestion?

Thanks in advance to anyone would give me his experience is such application

 

[EdStainless]

316 would not be a good choice for that application. Pitting is going to happen, and CSCC is a real risk.


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P.E. Metallurgy, Plymouth Tube

 

[pradipgoswami]

Your best bet would be opt for Nickel based alloys.

http://www.specialmetals.com/markets/oil-and-gas.html

may provide good resources for information for such working environments. Nickel base alloys may be expensive to start with, however may be cost effective in the long run.
The other option would be to think about Super Duplex products as against proposed AISI 316 grades. This will be cheaper than Nickel based alloys and moderately expensive that 316 S.S and may be attractive on a cost: lifespan ratio.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[GabrieleB]

Considering the content of H2S I would prefer to go to Superaustenic alloys in place of Superduplex. I read that duplex/superduplex material are more prone to SSC in H2S enviroment above 20KPa of partial pressure. The superaustenitic materials like UNS S31254 (254-SMO) has the same PREN of Superduplex, I suppose similar price, but with a better behaviour on H2S environment.

 

[SJones]

What specification and strength grade does the client require? 316L doesn't normally hit the strength requirements. 50 kPa pH2S takes you beyond the ISO 15156 limits for super duplex anyway. The only issue that remains for you and your client in selecting a material is: how much do you trust the statement "See Remarks column" for chloride and pH restrictions, or more correctly, lack thereof.

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.

 

[EdStainless]

The 7%Mo superaustenitics (AL-6XN and 654SMo) are more expensive than superduplex alloys.
They are 21%Ni 7.5%Mo were 2507 is roughly 7%Ni and 5%Mo.
With Ni at $6/lb and Mo at $12/lb it adds up fast.
The SA alloys are strong, but not as strong as the SD.
The real question is why won't steel work?


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P.E. Metallurgy, Plymouth Tube

 

[GabrieleB]

The answer is that the Carbon Steel has already failed, in 2 years is completely destroied (in some points the casing pipe is perforated by the corrosin) and they has to replace with a better material.

 

[EdStainless]

Where did the casing fail, deep or near the top?
In general SS has issues hear the top of a well where temps are cooler and acid gas condensation is a big issue.
What inhibitors were you injecting?
How much water? How much CO2?
Realize that you are talking about casing that will be 50x the price and strictly custom made.
You might actually be able to find some 625 tubular, but again be warned about the near top of hole issues.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

Assuming the corrosion issue occurs on the soil side of the casing, did the client investigate cathodic protection?

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]

Does it need to conform to API Specifications ? Hard to think it could meet anything more then H 40 or K 55. Also , I expect serious thread galling, API or proprietary threads. Chloride SCC should happen , but it doesn't always do what we expect. API 13 Cr would be much more available and could have a practical life. Incoloy 825 ( whatever UNS ) has been used down hole; The one time I saw it, it was in excellent shape after about a year -- some terrible wells but I don't remember specifics , certainly hot, H2S, Cl, and CO 2 . If 316 could be justified cost for this well , I guess you need something like 8 5/8 ", so Very few mills around the world that can make it. Also , what about the tubing ; 3.5 or 4.5 " and again few mills that can make 825 ( or any other high alloy) to API dimensions.

 

[EdStainless]

It is far more typical to use 13Cr or 9-1 for this application.
they have high strength, immunity to CSCC, and enough corrosion resistance in an oxygen free environment to survive with little inhibitor treatment.
I have seen fields in the same Cl and pH range using 9Cr 1Mo for decades.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

The problem for 13Cr or 9Cr-1Mo is the 50 kPa H[sub]2[/sub]S. They are fine in purely sweet environments, but things get tricky in sour conditions.

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.

 

[EdStainless]

SJones, Yes, but I have seen cases (majors companies) where they have internal guidelines for higher temper temperatures, reduced strength, and reduced allowed stress for using these alloys in sour conditions. And they work very well.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

Ed: i.e. 'tricky' as in not straightforward

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.

 

[EdStainless]

Yes Steve, definitely tricky.
But not as difficult as getting an austenitic alloy to survive as casing.

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P.E. Metallurgy, Plymouth Tube