Nitronic 60 in H2SO4

[RedVette]

Hello, everyone.

Would someone here happen to have data on the corrosion rate of annealed Nitronic 60 in either 10% or 20% sulfuric acid @ either 80° C or boiling? The information on metal supplier brochures only specify the 2% and 5% @ 80° C.

Any input is greatly appreciated.

 

[unclesyd]

I would strongly suspect than it will rapidly fail as the N60 corrosion resistance is compared with the corrosion resistance of 304 SS. Even though I haven't specifically tested N60 in the H2SO4 concentrations in the OP 304 SS would fail.

The consecrations in the OP are very hard to handle, especially if the fluid is heated.

 

[RedVette]

Unclesyd,

Thank you very much for your input.

Concerning the 'failure' terminology in conjunction with these grades in sulfuric acid, I understand that the reaction is the conversion of the surface mass into sulfate until all the exposed area is consumed. My question, then, is whether this sulfate buildup is in the like manner of corroded layers of the alternative material, carbon steel, under the same application, where the corrosion extends to a point, then stops as long as the layer is left alone and not scraped off? Or does corrosion continue until the entire volume of the stainless steel is penetrated?

Thanks again for your help.

 

[unclesyd]

Carbon Steel will not last any time in your acid concentrations. You have to be above 93% for the sulfate layer plays a part in the corrosion equation. At 93% forms the sulfate layer which protects the CS. Ferrous sulfate is insoluble in acid above 95% and any any exposure below 93% acid the sulfate will be soluble. The sulfate layer is rapidly removed by velocity and in the dilution of the 93%, and any Oxygen infiltration. The ingress of Oxygen will cause problems with he 93%.
In your acid concentrations you have attack the corrosion problem with very specific (expensive) alloys depending concentrations, temperature, and any contaminates. You will hear that someone is using Sulphuric at the lower concentrations but these people are using and inhibitor which will slow the corrosion rate down, but not get it to zero.

There is no way I would consider using CS below the 93% concentration.

 

[EdStainless]

10% at 80C is about the limit for alloy 20, AL-6XN, and 825.
You can't get over 2.5% in hot acid with the 3xx series alloys, even N60.
The issue is with how oxidizing the acid is, if there is forced aireation or oxidizing ions then you can push hotter.
Nitronic 50 would be a slight improvement.

Find a copy of MTI MS-1, it is an excellent guide to sulfuric service.


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Plymouth Tube

 

[RedVette]

Unclesyd,

Thank you for the valuable information. I never knew about the sulfate solubility dependency on acid concentration. I'll be sure to not forget it.

Other than Nitronic 60, I've considered Haynes HR-160, 118, 556, and 254 SMO as alternatives, but their cost is significantly higher. However, given the greater resistance and reduced change intervals, it would undoubtedly be a worthwile investment.

EdStainless,

Thank you very much for the sulfuric service guide. My step father used to work as an electrician for a railroad company and might have access to a copy. If not, I'm sure I can find a copy from Amazon or eBay. Checking Electralloy's brochure, Nitronic 50 is indeed substantially better than 60, though still insufficient.

By the way, just out of curiosity, is Armco Nitronic 60 to Carptenter Tech Gall-Tough as Coke is to Pepsi? I initially thought the two were the same thing under different brand names, but it seems N-60 seems to be better attributed for corrosion resistance. Hypothetically, if either of the two were to be vacuum/arc remelted during production, would the alloy exhibit any measurable improvement to its corrosion properties?

Thank you both again.