Do you want the original color to show?  If so, try a transparent polymer - perhaps a two-layer system such as epoxy base plus urethane outer.

CoryPad,
Yes we want the colors to show.  No coatings are allowed.  The museum says no coating. Any other suggestions?

If you can't coat a carbon steel piece, then you need to control the atmosphere - minimize humidity.  

I'm not a corrosion engineer or even a materials engineer so don't take these suggestions to heart until one of the experts like CoryPad or mcguire debunks them first.

1. Its not that big a piece, would mounting it on a zinc plated stand help?

2. Would active cathodic protection help?

3. Failing that, would sticking it under a heat lamp to help keep it dry be any use?

Hush,

I don't think item 1 will help much since there is not a strong galvanic cell (no electrolyte), which is how zinc protects iron.

Items 2 and 3 are potentially great ideas.  While an electrically conductive wire would need to be attached to the museum object, perhaps it could be mounted to the base and the wire/anode/electrical system hidden from view.

I'm with CoryPad. #2 sounds good. I would be afraid #3 would accelerate corrosion by increasing temperature without eliminating moisture.

I agree that the active cathodic protection sounds good.  Are you sure that "no coatings" can be used?  A very thin layer of a transparent polymer or even some type of shellac would provide the necessary corrosion resistance, and would not change the metallic appearance, save for the change in gloss.  I would find out the exact reason for the museum objecting to the use of coatings, because it may be mostly aesthetic-- no change in color, no change in metallic appearance, etc., which can be overcome with proper coating selection and application.

Thanks for the responses.  Item 2 was considered and rejected by the museum, they felt that the ICCP system would have to be maintained at a cost.  

Item 1 was rejected for the reasons that CoryPad gave, no strong galvanic cell to offer protection.  I think you need 650 Mv potential for protection, which is why I think Item 2 has some merits, as well.

The museum does not want to coat the piece because they do not want to change the appearance.  They  do have aesthetic concerns.  

Any other considerations?

ENC...

I am a bit puzzled and curious by the description of "rare" A36 steel. If this is a piece of the WTC, OKC Murrow Federal bldg (sp?), Edmund Fiztgerald, Titanic, etc... then the MOUNT design [fixed or floating]... and physical security... may be as significant issues as corrosion protection.

IF NO coatings are allowed, then I doubt if A36 steel would survive long without rusting.

Suggest You discuss possibility of using a thin coating of Corrosion Protective Compounds [CPC] in a continuous maintenance scenario. This coating will produce a slightly glossy appearance, but is none-the-less "temporary" and esily removed. The coating would require maintenance on a frequent-periodic basis as follows: remove the "object" from its mount; solvent clean it to remove the old CPC, grime, dust, "bird-shit", etc;  re-apply a new thin/wet CPC film-coating and allow to "dry"; restore object to it's mount. Avoid handling with anything but clean cotton cheesecloth or gloves. The object could last for years like this with minimal rust.

As previously suggested, I think that if the mount [or a hidden attachment to the mount] is anodic to the "object", that would be "good" also [especially if it is easily replaced].

An other idea is to allow [or chemically force] the surface to develop a protective rust patina to form. If this rust remains undisturbed by handling or other factors, it could outlast us all! Caution: This may/may-not be advisable in a highly poluted/wet [seacoast] atmosphere... but in a dryer/cleaner climate may work very well.

Another Idea would be to carefully apply a thick copper-plating to the object... and allow a beautiful copper-green patina to form [under similar circumstances as mentioned in previous paragraph]. Curators may not "like" this idea... but the Statue of Liberty is a great example of copper-patina protection... even in a seacoat environment!

Regards, Wil Taylor

Ask the museum to be responsible, too. Who would want to display an artifact in a mode which endangered it. Would they hang a painting outside?

You mention you want the original color to show? I'm assuming then the piece is already corroded or heat discolored. If that's the case I'm guessing the only way to maintain the color/discoloration is with a coating or by placing the object in an inert atmosphere.

ENC,
If you are still around there is a coating that will protect the metal and not change the appearence. The coating is Molykote "Metal Protectrant".

www.molykote.com

if this is really irreplaceable then the only safe place is in a hemetical sealed and controlled environment preferrably in a dry nitrogen (or equivalent) atmosphere.

before committing to its placement outside, you need to perform actual test with coupons if the same material. the tests and analysis of the results needs to be performed by a competent corrosion specialist.