stainless steel and brass

[chunkolini]

Linking to my thread regards keeping it shiny.

Hubby of my customer is a dab hand with a lathe, making clocks and steam engines as a hobby. I am thinking of asking him if he would like to turn up a pair of eyes for the fish sculpture. I figure they would have to be bolted on, that is no problem.

Would there be any problems having the metals in contact with each other? eg streaking of the stainless or corrosion etc. If this is the case would a simple plastic gasket between them stop this?

Chunko'.

 

[Shox Dr]

Well according to this site SS and Brass have a .10v on the Anodic Index, and anything less than .15v is preferred.


quote;
Galvanic Compatibility

Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating. The finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion.

For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the "Anodic Index". For example; gold - silver would have a difference of 0.15V being acceptable.
For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the "Anodic Index".
For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.

 

[TechnicAl]

I would use the gasket. If only to be on the safe side.

Shox Dr...........Firstly Im not saying you are wrong but some of those tables can be misleading. For example with Aluminium they often quote the figures for pure Aluminium which is very reactive but in practice (due to its reactivity) pure Aluminium rarely exists. It is almost invariably covered with a layer of Aluminium Oxide. Look at the results for Al2O3 and they are a lot different.
Stainless also has a passive layer.

Thats all....just a word of caution

 

[Drains]

Re Shox Dr vs TechnicAl - If you were dipping the thing in seawater on a regular basis, it might, almost, be worthwhile using a gasket (but it wouldn't as the voltage difference is so small)

Otherwise, you'll hardly ever see galvanic action except in a saltwater (boat or dockside), or hot (inside your radiator system) environment.

Most of the time it's perfectly reasonable to expect to get away with it, for at least 40 years.

 

[TechnicAl]

http://www.hghouston.com/coppers/brass78.htm

see "relative area effects"

I really dont know one way or the other but Id err on the safe side for the sake of a couple of bits of plastic

Thats all

 

[Drains]

From your link Al

The possibility of galvanically accelerated dezincification of an alpha-beta brass valve bolted to a flange on a large copper vessel is not eliminated, or even reduced, simply by fitting an insulating gasket between the two, since they will remain connected through the bolts. It is necessary also to fit insulating washers under the bolt heads and insulating bushes in the holes drilled in the flange of the valve.​

A couple of bits of plastic? Are you sure? I know the subject is dezinctification but it applies to all galvanic issues.
Having been a messer about in boats for a while, observing the nasty corrosive effects of galvanic action and seawater, I can honestly say the issue in freshwater is minor in most circumstances, and worth ignoring, unless there are likely to be substantial voltages present.

 

[TechnicAl]

I think dezincification is a different issue. I dont think its galvanic. This is really beyond my limits but I think dezincification occurs in Brass in freshwater which is why they use St Steel props for freshwater and Brass / Bronze for saltwater. The St St isnt good in saltwater. I believe its due to Oxygen in the water but dont take my word for it.

As Ive said its beyond me but I still think Id use the gaskets even if they theoretically dont do anything.

 

[chunkolini]

I did wonder if this one might open a can of worms.
I figure a thin plastic gasket wont hurt.
90% chance that I gets the job.

What effects might the galvanic thingy have?
Night night .

Chunko'.

 

[gordon stephenson]

Don't forget Chunko, you will have to insulate both sides and sleeve the thread with insulation for complete protection, We had to do the same to the side covers on power station generator bearing pedestals. Check for continuity when you have finished!!!
Seems a bit excessive,unless you live in an overkill sort of world.

 

[mike os]

turn it in stainless & heat colour it?

http://www.bssa.org.uk/topics.php?article=140

don't know about durability of the finish but recall that it is supposed to be good as long as not abraded?

 

[Drains]

Sorry Al. I wasn't being clear. I was trying to point out the necessity of complete isolation of the parts for any reasonable anti-galvanic effect - eg - any connecting bolts also need to be included in the chain of isolation.

I can tell you taht boaties argue endlessly about the need for anodes - (zinc, aluminium or magnesium depending on water - salt, brackish or fresh), or having none at all. I've certainly heard people say that they have added anodes on recommendation, only to watch their boat's metal bits corroding almost before their eyes.

Similarly some folk recommend isolating dissimilar metals, earthing odd metal bits (esp on wooden and GRP boats) while others swear doing nothing has just as much effect. Science, it aint.

The biggest issues are salt and/or electricity (stray voltages underwater from one shore-powered boat to another causing one boat to become a sacrificial anode, nasty).

As a result of all this I have paid attention to bits and pieces that have been left outside, and have noticed that on the whole, most things last well, even when a bit damp. Of course steel rusts and aluminium oxidises, but even when you put them next to stainless and brass, any corrosive effect seldom appears to be local, so my assumption is that it's something in normal (non engineering) practice one can ignore, although a good coat of paint to keep the rain off, and a handy dod of grease certainly put the mind at rest.

The general rule though, which can't be argued with, is keep everything the same!

 

[lexi]

Modern Jap outboard manufacturers are always extolling the virtues of SS in gearcasing and impellors etc. Maybe that's why they dont last well

Old Seagull engines made use of brass and bronze to go with heavy alloy.

 

[TechnicAl]

Drains
Dont get me wrong Im sort of agreeing with you really. Im coming from the point of view of an advisor so you tend to err on the safe side.

One thing I do disagree with is, it is definitely SCIENCE but its Chemistry and Im a Metallurgist. It is very complex and like you say electricity can play a big part.

I had a boat once upon a time but it was plastic and even that corrodes (osmosis) so you are never immune.

 

[chriskelland]

Hi All,

Could you not use bronze? I know the colour is very slightly different. Model boilers use bronze for all boiler fittings due to de-zincification. You can usually tell when this occurs as the colour of the brass changes and seems to go darker.

Chris.

 

[chunkolini]

This is all getting very elaborate (but interesting).
All we are thinking about is cosmetics, my main concern is will we get grotty streaks appearing below the eye over time.

Chunko'.

 

[Drains]

Drains
Dont get me wrong Im sort of agreeing with you really. Im coming from the point of view of an advisor so you tend to err on the safe side.

Absolutely! And your advice is correct. Science? Well it's a very obscure one at the layman's end, as nobody seems to have a clue what they're talking about, and I've seen chemists proved wrong.

However, the question is, will Chunkos job look grotty if he doesn't isolate the parts?

Let's face it, it might look grotty whatever he does

 

[outofthefire]

If your polishing the brass and want it to stay polished you'll have to clear coat it with something which would insulate the parts if you want it to get a patina naturally i'd just suck it and see, if its bolted together at the worst you can strip it apart and isolate them properly at a later date.

 

[chunkolini]

Grotty streaks anybody?

ie will I get water off the brass leaving sny kind of deposits on the stainless?

Chunko'.

 

[Drains]

No, I reckon not Chunko. Go for it.

Is that what you've been waiting for?

 

[chunkolini]

Cheers Mr Drains

That clarifies things a bit, next we are waiting for my customer to get back from the caribean and confirm what I a doing.

Chunko'.