Monel vs 316SS (on Sulfuric acid %5/%95)

[keclose]

We are planning to use Monel 400 for two different sulfuric acid lines of which concentrations are %5 and %95. What do you think the corrosion resistance performance of Monel will be?
Better than 316SS, same or worse?
Kerem.

 

[metengr]

What is the service temperature(s) at these concentrations?

 

[keclose]

Sulfuric acid is pumped from a day tank at normal conditions.
No special heating or cooling.
The discharge pressure of the pump is 3 bar.
Monel will be used both in discharge and suction.
Kerem.

 

[CoryPad]

You can read about the corrosion resistance of Monel 400 exposed to sulfuric acid here:

http://www.specialmetals.com/documents/SM Aqueous Corrosion Book.pdf

You should be okay with the 5%, maybe not with the 95%. Here is an excerpt:

"In practice, MONEL alloy 400 has shown satisfactory
resistance in the storage of 80% acid at room temperature,
but should not be used continuously with pure acid of
higher concentration without preliminary tests."

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[metengr]

keclose;
I would recommend you review the article below from the Nickel Development (NiDI) Inst, titled " Selection and Performance of stainless steels and other nickel-bearing alloys in sulphuric acid" by C. Schillmoller (NiDI Technical Series No 10057.

http://www.nidi.org/index.cfm/ci_id/80.htm

Also, a second excellent resource material to review is from Special Metals, at their web site below,and go to the tab Products and look for General Technical Information. The material of interest is titled High-Performance Alloys for Resistance to Aqueous Corrosion;

http://www.specialmetals.com/

Summary, Monel is not recommended for handling sulphuric acid concentrations above 50% by weight. So, I would not consider Monel, period. If your specified concentrations are what you state, 20Cb-3 would be even a better selection in comparison to 316L at least for the discharge piping because of fluid velocity effects on corrosion resistance.

Go to the Carpenter web site below, register for free to access their technical information

http://www.cartech.com/

Find the 20Cb-3 alloy and look for the isocorrosion chart for sulfuric acid.