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Wallace · Posted: Tue Nov 21, 2006 9:24 am Post subject: Dezincification

I spoke to my brother about my boiler corrosion.
He said it's probably dezincification.

He's not sure why firing a boiler helps avoid corrosion as you can't really anneal it unless it's heated red hot (that is apparently annealing)

But basically he said brass is copper and zinc. The white stuff I described he said would be the zinc breaking up, the copper colour is literally copper that is left.

So i did a search, and here is the first result

http://www.corrosion-doctors.org/Forms/dezinc.htm

Still at a lost to why steaming engine can help.
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yosa · Posted: Tue Nov 21, 2006 9:38 am Post subject:

Nice work finding that one Wallace. I think the answer is in the article you've posted. i.e.

Conditions favoring dezincification are contact with slightly acid or alkaline water. Not highly aerated, low rates of flow of the circulating liquid, relatively high tube-wall temperatures and permeable deposits or coatings over the tube surface.

Acid or Alkakine water could well be left in the boiler. There would be no aeration or flow of circulating water in a standing boiler.

I think it's the topping up or replacing of the water, rather than the steaming in itself, which removes both of these conditions.
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Wallace · Posted: Tue Nov 21, 2006 10:56 am Post subject:

No worries.

It was only cos my brother had heard of it as a plumber, and some of the higher quality tap fittings are labelled "dezincification resistant".

By the looks of it, the less zinc then all the better.

He's glad he made his boiler for his scratch built engine from copper now

Just to add, I am leaning toward the theory of firing the engine often helps isn't as true anymore. It's just now water use and storage
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yosa · Posted: Tue Nov 21, 2006 11:19 am Post subject:

I wonder does the engine age give an indication of possible problems. By that I mean, has this phenomenon only been noticed relatively recently, and therefore is reduced zinc content fairly modern?

The worry being that the brass on all our "old" engines might have a high zinc content and so be particularly vulnerable.

On the issue of high alkaline content encouraging the problem, it underlines the good practice of using distilled water if possible.
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Wallace · Posted: Tue Nov 21, 2006 11:27 am Post subject:

I'm not too sure. it's certainly a possibility.

I would have a guess that the older the better. More "pure" so to speak?

Whatever brass Australia used during production of ammunition during World War 2 is good though.
The army used my Grandfathers property for training.

As a kid in the 80's I found heaps of old casings which I still have, in perfect condition

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yosa · Posted: Tue Nov 21, 2006 11:38 am Post subject:

Wallace · Posted: Tue Nov 21, 2006 11:57 am Post subject:

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Mamodman123 · Posted: Tue Nov 21, 2006 12:12 pm Post subject:

There we go then. I always thought that not firing an engine couldn't make the boiler corrode
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SPOKESMAN · Guest

Perhaps using distilled or de-ionised water would help?

Wallace · Posted: Tue Nov 21, 2006 12:18 pm Post subject:

Mamodman123 · Posted: Tue Nov 21, 2006 12:24 pm Post subject:

Wallace · Posted: Tue Nov 21, 2006 12:26 pm Post subject:

Nah, they heat it up, red hot, then let cool.

It makes it more bendy/softer.

Take the piping from an engine. I can't tell if it's been annealed or not, seems to be as it's easier to bend.

But if you needed a neat bend, heat it right up, then let cool

Then you can get a nice bend in that part.

Brother said it's common to do with copper pipe in plumbing
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MooseMan · Posted: Tue Nov 21, 2006 1:10 pm Post subject:

mj · Guest

http://en.wikipedia.org/wiki/Brass

A bit more about brass, if your interested

The boiler corrosion, is the same as you get on the top of domestic hot water cilynders ( not if you use dzr brass couplings).
Impurities in the water reacting with the zinc in the brass.
Localised water supplies differ greatly around the country with various elements being present which all have differing effects on the brass.
The brass used in models is probably 'low brass' which has high zinc content. Pre ww2 brass used was of a much lower zinc content i
would think, as you see less 'white spots' on older models.