Stainless or Monel?

[Duncan Gibbs]

From my Dragon thread:

One question I have for the metallurgists on the Forum is, are my screws monel? One of these from the covering board is quite obviously silicon bronze, but the other, from the planking, I'm not sure about. Rick and Peter both think it may be monel and it does have a bit of verdigris on it, which I would presume can't build up on stainless as it doesn't have any constituent copper in it, but is there a sure way of knowing?

[P-man]

did you try passing a magnet over it? some stainless steels will display weak magnetic properties. of course if the magnet doesn't react, you're still not sure.

edited to add: useless suggestion. i didn't know monel can be slightly magnetic also.

[Duncan Gibbs]

A magnet does nothing to the SB screw but will weakly pick up the screw in question. According to wiki nickel, the prime constituent of monel is magnetic at room temperature, but some monels are non-magnetic.

[P-man]

perhaps this might help (from http://preservapedia.org/Monel ): A slightly more advanced method of identification involves exposing the metal to be identified to a small amount of nitric acid. Nitric acid will react with the copper and nickel contained in Monel and cause it to turn a blue-green color. Nitric acid produces toxic fumes and should only be used in a well ventilated area. In addition, proper safety gear including rubber gloves and a face mask should be worn. To avoid disfigurement of the object under examination, tests should be performed in an inconspicuous location.

[Paul Pless]

A magnet does nothing to the SB screw but will weakly pick up the screw in question. According to wiki nickel, the prime constituent of monel is magnetic at room temperature, but some monels are non-magnetic.

Monel also contains some Fe right?

[Duncan Gibbs]

Just found this:

http://forum.woodenboat.com/showthre...l-or-Stainless

Gary has the grinder test. Will give it a shot in the morning.

[Duncan Gibbs]

Righto! Got some nitric acid from a local scientific laboratory and some cloudy ammonia (a very weak ammonium hydroxide with a soap content) and set myself up to conduct the test, with water, gloves, goggles, instructions from the thread linked to above and a plastic pipette:





First step was to drop nitric acid onto the bare surface. When I took the lid off the jar with the nitric in it fume/vapour trails immediately started to emit from the jar. You can't quite see it from the photograph but the head of the screw is bubbling here:



So I know it's not stainless at this point, but the ammonium hydroxide, even though in a weak solution, settles it with a distinctive blue blob in the middle of the chemical cocktail sitting atop the screw head:



Monel 400!

Next question: How much would one expect to pay for such a fastening? My guesstimate is about $3.00 - 4.00 (AUD/US)

[The Bigfella]

My first thought on seeing the thread title was... where's he going to source those?

I've got heaps of old ones... but they aren't much good.

[SMARTINSEN]

If they are in reasonably good shape, and the slots are not all buggered up, why can't you re-use them?

[RFNK]

Really good news that they're monel. I think most of them are in good shape aren't they? You probably won't have to buy many at all. If they're all monel and you need some more, you could always replace some topsides ones with SS and use the old topsides monel ones below the waterline. But if I recall correctly, they're just about all okay anyway.

Let me know if you don't want them!

Rick

[Duncan Gibbs]

I have yet to come across one that is in any state of decrepitude. The idea is that as I replace frames I unscrew each set, clean them up and rescrew them into the newer laminated timbers, dipped in red-lead of course.

Ian, I dare say your Dragon would be similarly fastened being of a similar age: 10 years older IIRC? The chap who we borrowed the trailer from, his Dragon was monel fastened in its planking. Must have been the standard for Sydney about that time.

[bloggs68]

Duncan,

what size are they?

AD

[Duncan Gibbs]

They're about 8/10G x 40/45mm Andrew. Even with maximum persuasion there's very little damage to the slots or heads. Bloody hard is what they are!