Monel 401- galvanic compatibility 2

[Pichy]

We are in need of a stainless alloy to use for building components in contact with Monel. Our particular Monel alloy has been tested to have 50.5% Copper & 49.5% Nickel, and is therefore closest to Monel 401. I have not been able to find this on any galvanic chart. What stainless alloy can we use (in atmospheric conditions) for fasteners and replacement components to minimize corrosion with the existing Monel? Thanks.

 

[TVP]

Why can't you use fasteners fabricated from a Monel alloy?

 

[Pichy]

The cost of the monel is prohibitive. We are using it for exposed components, but the concealed backup plates, shims & fasteners can be stainless or some other compatible metal. The original components that we are replacing were of steel, and have either completely disappeared or are severely corroded, 50 years after original installation. We're hoping to get 100 plus years out of this work.

 

[EdStainless]

If you want 100 years you will need to use Monel hardware. I believe that

http://www.grandeurfasteners.com/home1.html

these guys still work in Monel. You may want to use K-500 for bolts. It can be age hardened to make it stronger.

Even though the hardware is concealed I would suggest that you only use HIGH alloy materials. If you want to use stainless, look at the 6%Mo alloys such as AL-6XN or 254SMO. I would discurage the use of 304 or 316.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Pichy]

Do you mean 304 & 316 active? What about 304 & 316 passive? They are more noble than Monel 400 on the charts. Wouldn't that make for a good match, provided the stainless components are smaller than the monel?

 

[EdStainless]

There are a couple of problems.
One is that you don't know what kind of impurities/corrosives are going to collect over the years. The tendancy for 3XX alloys to pit and stress crack do not bode well for long term usage.
You can't assure that they will remain passive. That is the catch.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[kenvlach]

If you don't want to use Monel fasteners, there are some bronzes worth considering.

For galvanic compatibility, see MIL-STD-889B, available at

http://assist1.daps.dla.mil/quicksearch/

From Table I in Notice 3:

High-copper bronzes, category “N” are compatible with category “O,” high-nickel copper alloys such as Monel for both industrial and marine atmospheres (although not seawater immersion).

A Galvanic Table listing metals in the order of their relative activity in seawater at

http://www.corrosion-doctors.org/Aircraft/galvseri-table.htm

list a Phosphor Bronze 534 (B-1) immediately above Monel, and a silicon bronze 655 seven places below.

The Copper Development Association at

http://www.copper.org

has a lot of searchable information. E.g.,

MATERIALS SELECTION FOR HIGH RELIABILITY COPPER ALLOY SEAWATER SYSTEMS [includes Cu-Ni alloys]

http://www.copper.org/applications/cuni/txt_materials_selection.html

Aluminum Bronze Alloys - Corrosion Resistance Guide, Publication No 80, 26 pages of invaluable data on recommended service environments.

http://www.cda.org.uk/Megab2/corr_rs/pub80/default.htm

Copper & Copper Alloy Corrosion Resistance Database

http://protection.copper.org/

Corrosion Resistance of Copper and Copper Alloys (Large Table), CDA No 106

http://www.cda.org.uk/Megab2/corr_rs/corrosio.htm

Collation of Data Comparing Properties of Aluminum Bronze with Cast Stainless Steels and Ni-Resist in Offshore Sea Water Environments

http://www.cda.org.uk/Megab2/corr_rs/pub115/default.htm

 

[EdStainless]

I didn't even think of NAB. Good idea.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm