Comparative wet intergranular corrosion testing of super alloys

[Feldmann359]

Dear colleagues!

I am currently engaged in a project evaluating several Ni/Co/Fe-base cast and wrought super alloys with respect to their sensitivity
towards wet intergranular corrosion.

Within our product, temperatures up tp 1000-1500 F may occur, followed by colder phases where corrosive liquids like nitrous acid, water, salts etc will be present.

I am wondering, which laboratory testing method ist best suited here.

ASTM A 262 Prac C. (Huey Test) seems to be appropriate only for austenitic stainless steels (not for high Cr/Ni super alloys?)

ASTM G-28 (Standard Test Methods for Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys) is not suitable for cast alloys.

Or is there a better solution? Unfortunately, testing the alloy in the real environment is to costly, so a cheaper pre-selection test is needed.

Thank you very much in advance for your help
Feldmann

 

[metengr]

Or is there a better solution? Unfortunately, testing the alloy in the real environment is to costly, so a cheaper pre-selection test is needed.

Perhaps or have you thought about a corrosion coupon rack? Very affordable and actual service conditions are evaluated using small material coupons. In your environment, I would use a corrosion coupon rack for several months service and evaluate test results.

 

[Metalhead97]

Feldmann359,

You can apply ASTM G-28 to cast alloys just remember cast alloys tend to have larger grains and more segregation issues, which will contribute to a poorer performance.

MH

 

[Feldmann359]

Dear colleagues,

Thank you for your replies.

A coupon rack test is unfortunately not applicable here, because
the real environment is a very small combustor using a hydrazine and NTO as fuel.

So the real corrosion attack will be a combined intergranular attack (during non operating case, when moisture plus combustion residuals form nitrous acid and nitrates), attack from liquid hydrazine and the strong oxidant NTO as well as hot gas corrosion (oxidation etc) when the combustor operates.

So my approach is to validate the material candidates in a series
of tests, beginning with the resistance to intergranular corrosion test after heating/welding of the specimen for sensitization.

Does anybody know what type of corrosion test would be best for a first comparative screening of the selected group of Ni/Fe/Co superalloys?

Is the Huey Test according to ASTM A-262 definitely not recommended here?

Best regards
Feldmann

 

[Metalhead97]

Feldmann,

It sounds like the Huey Test (boiling nitric acid) would model the non-operational corrosion that takes place. Go with that. A word of advice, don't be handy-capped by specs. Yes, many common procedures need to be done to a certain spec (ASTM, MIL, AWS, etc.) per customer requirements, but when you are doing new stuff there isn't always a spec to guide you and that's when the engineering comes in.

MH

 

[SJones]

Try NACE Corrosion 2007, Paper 07202

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[Feldmann359]

Thanks very much for your assessment!

 

[metengr]

Feldmann359;
I think you need to really re-think your strategy of using A-262 to evaluate corrosion performance for your stated service conditions. You have two corrosion concerns to evaluate - hot corrosion exposure and intermittent exposure to liquid conditions. I think relying solely on this practice will not give you your intended results.

 

[Feldmann359]

Thanks metengr;
Of course, I have to perform at least two corrosion test campaigns, because I have in field service wet intergranular as well as hot corrosion attack. I wanted to start with the wet integranular case because there are standards and the test is relatively easy and affordable.