Brass and boilers

[AndrewP]

Why, if brass is a no-no in contact with steam is it specified for the inner dome and regulator tube on my Rob Roy?

These are both quite thick components admittedly so I assume any deterioration will take a long time to manifest itself but surely it can't be that simple.

puzzled
Andy

[simonwass]

I know someone who even made his boiler bushes from brass. The loco is over 30 years old and hasnt had any problems. I wouldnt chance it though.
Not sure about a problem with something just in contact with steam, the problem as I understand it has to do with stuff under water, electrolytic action. I've made internal regulators from brass and I'm sure thousands more have done so too.

[abby]

Mamods had brass boilers and cylinders with no detrimental results as far as I know , but it may be that wet steam is ok with brass but not superheated.
Abby.

[simonwass]

May be an all brass boiler will not have anything to cause electrolytic action, do dissimilar materials?

[AndrewP]

Ok I did some digging:-

Two factors that can increase the probability and rate of dezincification occurring in service are elevated temperature and coupling to a more noble metal. If brass bosses are used on copper hot water cylinders the combined effects of the high water temperature and coupling to a large area of copper can give rise to significant dezincification even in waters that normally give no trouble at all. Consequently this is one point in a domestic plumbing system where brasses are not used; the British standards covering the construction of copper water cylinders specifically require the bosses to be of dezincification-resistant materials.

extract from article here www.hghouston.com/coppers/brass75.htm

Also covered in wikipedia.

It would appear that CZ132 is the magic alloy (contains 0.03% arsenic) but heat cycling as in silver soldering can destroy it's resistance to dezincification.

Presence of moisture and oxygen required, attachment to large lumps of copper and elevated temperatures speed it up - sounds like a boiler to me!

Now where did I put that big lump of gunmetal?

Cheers, Andy

[standardsteam]

I think there are certain types of brass alloy that inhibit de-zincification in some environments such as Admiralty brass (which I thought had arsenic as one of it constituents).

[alanstepney]

There are many varieties of brass.
Some are more, or less, resistant to dezincification than others.

Best advice is to avoid it completely in boilers and parts directly connected thereto.
Where it is used, those parts should be checked or preferably replaced, frequently.

As for Mamod, many of their boilers are steel, coated with brass.

[havoc]

I find all this strange. In germany, the prefered material for boilers is brass. This is written into all of their model engineering guidelines I ever read.

[chameleonrob]

havoc said:

I find all this strange. In germany, the prefered material for boilers is brass. This is written into all of their model engineering guidelines I ever read.

is that brass defined the same way we do? I seen to remember that in the US that bronze is sometimes called red brass and is still suitable for boilers.

I believe that some brasses can be used on boilers but unless you really really know which grades are suitable and are sure that the material is to that spec then I would steer clear.

rob

[steammadman]

the brass bushes etc in my boiler, over 30 years old, show no signs of deteriation

[GWRdriver]

Because it can be relatively inexpensive (or once was) and is available in many sizes locally, for boiler bushings I often use a bronze known in the US as CDA-932 or SAE-660. This is a solid continuous cast bearing bronze, not the sintered variety. Because it does contain lead and zinc, I am occasionally asked to defend this material as being OK for boiler work, that is, not prone to dezincification, and compatible with silver solder.

The typical analysis is as follows:
Aluminum .005%
Antimony .35%
Copper 83%
Iron .20%
Lead 7%
Nickel 1%
Phosphorus .15%
Silicon .005%
Sulfur .08%
Tin 6.7%
Zinc 3%
www.anchorbronze.com/c93200.htm

To back my experience with a smattering of fact I contacted several manufacturers of bronze alloys and was told, first, that the 7% lead content is not enough to appreciably affect soldering qualities and I have found that to be the case. But the more importantly, apparently dezincification does not become a problem (so say they) until zinc content reaches beyond 9% which is well below the 25% to 40% zinc which constitutes a "brass" in the general sense of the word in the US.

I don't use anything classified as a brass, and if analysis is known then nothing above 10% zinc, in a permanently affixed structural component of my boilers.

[Shawki Shlemon]

In the Australian boiler code Brass is not allowed in any structural part of boilers , bushes dome etc.. for the above reasons .Solid copper is allowed to be used to make bushes .Not a very good material to work with but it is an alternative . It is not worth taking the risk and devalue the boiler hence the engine . I believe Marine Brass used by the Navy is as good as bronze but it is not easy to acquire and may be as expensive . Why risk it . Every thing may be sold one day , stay with the rules,that is my advice .