Engine anode question

[sailorman]

My replacement Nanni exhaust injection elbow is cast aluminium alloy rather than CI that the previous one was made in.
now as an engine anode NuBe i find the new alloy one has an anode beside the injection spigot, this anode was supplied with a copper washer :disgust:. i have fitted the anode threaded plug without the washer, just instant gasket to avoid corrosion due to the copper / aluminium alloy.
what would you have done

 

[VicS]

My replacement Nanni exhaust injection elbow is cast aluminium alloy rather than CI that the previous one was made in.
now as an engine anode NuBe i find the new alloy one has an anode beside the injection spigot, this anode was supplied with a copper washer :disgust:. i have fitted the anode threaded plug without the washer, just instant gasket to avoid corrosion due to the copper / aluminium alloy.
what would you have done

What is the plug in which the anode is mounted made of?

 

[sailorman]

What is the plug in which the anode is mounted made of?

yellow metal ?

 

[VicS]

yellow metal ?

So the copper washer would not have made things worse.

I hope your sealant is not preventing good electrical contact with the elbow.

 

[sailorman]

So the copper washer would not have made things worse.

I hope your sealant is not preventing good electrical contact with the elbow.

i had obviously thought about a good bond & only put sealant around the flange, not the threads.
adding copper to ali seemed all wrong

 

[vyv_cox]

Is the copper washer in contact with the seawater to any extent? I'm not familiar with the design but I assume there is some form of thread between the washer and the interior? In that case it won't do any harm at all.

 

[Hydrozoan]

I cannot see why there would be a problem, for the reasons already given. But also, if the injection elbow and anode came together - especially from Nanni - I'd trust the manufacturer. (Interesting BTW if Nanni have gone from CI to Al alloy - Beta went from SS to Al alloy some years ago.)

 

[VicS]

i had obviously thought about a good bond & only put sealant around the flange, not the threads.
adding copper to ali seemed all wrong

If you already have a "yellow metal", presumably brass, fitting in which the anode is mounted I cannot see that adding a cooper washer would cause any addition problems. Esp if as Vyv points out it wont be incontact with the water.

The brass holders for the anodes are what always puzzle me....... I suppose the area exposed to the water is relatively small

I'd put the sealant or Tefgel perhaps, on the threads and make sure there was good electrical contact through the copper washer.

 

[sailorman]

Thanks all
i have now added the copper washer.

 

[Hydrozoan]

The brass holders for the anodes are what always puzzle me.......

I'm a bit puzzled about your puzzlement - is that because of brass's propensity to chemical (rather than electrochemical) corrosion?

 

[sailorman]

de zincification i would assume

 

[Hydrozoan]

de zincification i would assume

When the brass is in immediate electrical contact with, and close proximity to, the mass of zinc? I would have thought that the latter would inhibit both electrochemical and chemical processes of de-zincification - but perhaps I'm missing something? Or do they just use resistant brasses?

Edit: De-zincification fundamentally involves the reaction Zn (metal, solid) = Zn2+ (ion, in solution) + 2e- (electrons). With a neighbouring mass of Zn doing its job of protecting the aluminium, there will be a high concentration of Zn2+ in the immediate solution. By Le Chatelier's principle, this will 'push' the above reaction back to the left, i.e. towards metallic zinc, thus inhibiting dezincification.

 

[VicS]

I'm a bit puzzled about your puzzlement - is that because of brass's propensity to chemical (rather than electrochemical) corrosion?

de zincification i would assume

When the brass is in immediate electrical contact with, and close proximity to, the mass of zinc? I would have thought that the latter would inhibit both electrochemical and chemical processes of de-zincification - but perhaps I'm missing something? Or do they just use resistant brasses?

Edit: De-zincification fundamentally involves the reaction Zn (metal, solid) = Zn2+ (ion, in solution) + 2e- (electrons). With a neighbouring mass of Zn doing its job of protecting the aluminium, there will be a high concentration of Zn2+ in the immediate solution. By Le Chatelier's principle, this will 'push' the above reaction back to the left, i.e. towards metallic zinc, thus inhibiting dezincification.

No I am not thinking about dezincification of the brass. I am thinking about the effect of brass on the anode, or the aluminium housing into which it is fitted.

The OP was worried about the effect of a copper washer. For the same reasons I am more concerned about the effects of the brass mounting for the anode. That will be in direct contact with the water unlike the copper washer which probably wont be.

 

[Hydrozoan]

No I am not thinking about dezincification of the brass. I am thinking about the effect of brass on the anode, or the aluminium housing into which it is fitted.

The OP was worried about the effect of a copper washer. For the same reasons I am more concerned about the effects of the brass mounting for the anode. That will be in direct contact with the water unlike the copper washer which probably wont be.

But won't any (potential) effect of the brass mounting - or the copper washer, come to that - on the aluminium be negated by the protective effect of the zinc?

 

[VicS]

But won't any (potential) effect of the brass mounting - or the copper washer, come to that - on the aluminium be negated by the protective effect of the zinc?

I am thinking it will accelerate the rate of loss of zinc ....... and if the anode is not replaced when depleted the aluminium will then be attacked.

 

[Hydrozoan]

I am thinking it will accelerate the rate of loss of zinc ....... and if the anode is not replaced when depleted the aluminium will then be attacked.

Thanks. Well, I suppose it could - a bit. But a very small 'bit' I think, taking into account the relatively great mass of aluminium nearby (and the relative positions of aluminium, zinc and brass in the electrochemical series). I had never given a second thought to the fact that my zinc engine anodes were mounted in brass, and your puzzlement had me worried - both about my acceptance of that, and about my rusty (or should I say de-zincifying ) physical chemistry!