Boiler fittings - is brass OK?

Thanks Jason. I needed some clarification because where I come from silver solder would be a specific and not generally regarded as brazing. I have seen comments on the web that anything over X C is brazing which seemed a bit crack pot to me. I'd be inclined to regard silver soldering as hard soldering. I'm not the only one either.

Going back to the OP's question he needs to see dezincification as brass rotting. That might give him a better idea of what is likely to happen. If he has looked at older designs that use brass for fittings he might see the comment good brass. I have. Brass just like other metals can come in a variety of flavours that are intended for specific purposes and have varying analysis, some more controlled than others. I suspect the older sources were trying to avoid cast brass that might be any old thing. Gunmetal seems to be cast too though and is still about - copper, tin and pretty low zinc content. Sort of weak bronze. Many bronzes have zinc in them.

Bronze comes in many flavours too. Natural bronze can be found by searching tin bronze - what it should be but some use aluminium or silicon and other bits and pieces. Many suppliers give information on fabrication. Solderability is usually stated as excellent. brazing as good - even for tin bronze. All probably down to tin melting at circa 230C. Lead melts at circa 320C. Some pundits mention that it has the effect of making silver solder less fluid. I'd wonder if it alloys with silver.

Silver melts at circ 960C, bit hot for an ordinary gas torch so out of curiosity I tried to find out what is in sliver solder. Model engineering etc sources don't give any info but a major supplier does - interesting, lots of zinc.

**LINK**

This sort of area annoys me - myths that may or may not be fact depending on what is actually used what ever it is. Just saying brass for boiler fittings though is a no no without more information and now it has a bad name that info wont be available.

John

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If anyone needs to get a life like me there is a decent run down on brasses here

**LINK**

There are others about and other "brasses"

Data sheets on many here and also some bronzes

**LINK**

I was interested for other reasons once and still am a bit. The problem with all of them is in the eutectics area aspects and 'orrid things like valencies.

John

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Avoid stainless steel like the plague if it is near the water in the boiler. Sounds daft I know, but unless you are certain you have the right grade, hot water under pressure can cause all sorts of problems. You are OK in superheaters as there shouldn't be liguid water

Wow. I read somewhere some attempts were made to make SS boilers and weld them. If my memory serves me right the conclusion was cracks can occur because of warm up and cool down cycles under stress (pressure).

Duncan - do you know what is the 'right grade'?

At work I have a lot of equipment made out of 304, 316, 316L grades.

See Table. 1: here:

http://www.parker.com/literature/Instrumentation%20Products%20Division/Catalogs/Bul%204200-TS%20-%20Feb2010%20-%20Final%20Low%20Res.pdf

Ajohnw - so SilverFlo55 contains 22% zinc but is ok. Is it ok because of no galvanic action?

I think we need a real metallurgist to comment on this one, I just take it from one that I knew at work (before I retired) that austenitic and hot water under stress is a problem. Presence of chloride ions makes it worse, and tap water contains traces of chloride, which get concentrated in a boiler as the water bois away leaving the chloride behind.

You provoked me to google this subject For the curious ones:

http://www.parrinst.com/wp-content/uploads/downloads/2011/07/Parr_Stainless-Steels-Corrosion-Info.pdf

https://en.wikipedia.org/wiki/Stress_corrosion_cracking

and some HSE report:

http://www.hse.gov.uk/research/rrpdf/rr902.pdf

I dont know if it helps, but "stainless steel" is just a generic term like "car" the range and diversity are almost limitless. from cutlery to aerospace ,mot only the nickel and chrome content can vary ,but other elements are added which completely change the characteristics of the material. so unless it is purely decorative,it useage needs to be specified and the correct grade obtained

so true

My son reckons that stainless corrodes - he looks at stainless saucepans which do and he lacks a technical education. School part covered it under the heading of resistant materials which seems to only exclude plastics.

Stainless is a broad field as are copper alloys and many other things.

John

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for making a proper silver soldered boiler out of copper there should be no 'short cuts' and only the proper materials used for bushes and stays.

when one considers the cost of the copper and silver solder the small extra to obtain the correct grade bronze for the bushes is very small.

if a jobs worth doing....

cheers,

julian