Brass Boilers

[DaveH]

I see a lot of info. on copper and steel boilers, very little on brass boilers.
Yet as a kid all bought Steam engines had brass boilers, or at least looked like brass.
Is there a reason not to use brass tube as boiler material?

Dave

 

[Mainer]

Other guys may know definitively, but it's my impression that brass is subject to cracking and the zinc leaching out of the copper alloy over time and is therefore Not Good. Use pure copper for model boilers.

 

[doc1955]

I see a lot of info. on copper and steel boilers, very little on brass boilers.
Yet as a kid all bought Steam engines had brass boilers, or at least looked like brass.
Is there a reason not to use brass tube as boiler material?

Dave

Boilers similar to these? These are actually older then I am (that is old!) and I am attempting to refurbish a couple out of the group. I have not seen any cracks so far not that I'm disputing this I am not well versed on boilers but I'm just saying.

 

[tel]

Brass is verboten as a boiler material in any code I know of - the dezincification being the main reason. The brass boilers found on the old ones are all of the toy, dribbler' type in my experience.

 

[Dan Rowe]

Tel,
Brass boilers are allowed in AMBSC Code Part 3 Sub-Minature Boilers 2.1.5. They are limited to low pressure defined as not exceeding 200kpa (29psi). 7.5.1 states the certificate is valid for one year only.

Brass boilers are still made for small toy or garden steamers the firm that comes to mind is Regner in Germany but I know other firms still make low pressure brass boilers.

The danger for the home builder is getting high guality brass most of it has way to much zinc to consider it suitable for boiler construction so copper is a much better choice of material.

Dan

 

[DaveH]

Thank you all - quite interesting.
I'm not at this time even thinking about building one, although I have built a couple of steam engines I run them on air.
I was looking in a model shop and there was a model steam engine in the window, with a nicely polished brass boiler.
I can't be 100% it was brass but sure looked like brass. I've heard/seen brass boilers can be dangerous and now I am wondering how is this allowed to make them basically as toys.
Something is not adding up here.
What am I missing here?

Dave

 

[DaveH]

It's OK Dan has given the missing bit.

So it is Brass but with a low zinc content. Ah now I see - No zinc = copper.

It's good when a plan comes together.

Thank you all

Dave

 

[tel]

You can always make a copper one and hide it under a nice shiny brass cleading.

 

[DaveH]

tel,
Now thats a good idea, I could tell every one it is brass running at 100psi and scare the living day lights of them ;D

Well, umh could be a good reason to make a boiler

Dave

 

[Mainer]

There are also about a million (well, half a million) alloys called "brass." I suppose conceivably some of them might be suitable for a boiler...but I would still recommend copper.

 

[CF-EKM]

Many Copper-Zink alloys carry the imminent danger of so called "stress corrosion cracking".
This phenomenum means a fast cracking of the material caused by the combination of
- mechanical stress
- under the influence of a specific media that will induce the cracking process

There are materials that aren't very sensitive for stress corrosion cracking, but there are materials too, that are very sensitive for this kind of failuring.
- many aluminium alloys
- most 'brass' alloys
- certain steels, f.ex. the very common 1.4301 ('V2A', X5CrNi18-10) steel
- ...

The different materials have certain media that are responsible for stress corrosion cracking. Brass alloys for example are often sensitive to ammonia substances.
The phenomenum of the mentioned stress corrosion cracking is widely investigated by sanitary industry - there are often parts made of brass alloys, that crack because of certain ingedients in the water flowing through them, under influence of inherent stresses (set in the production process or within their assembly).

All materials have, besides their specific attacking media, a certain highth of mechanical stress, that is necessary to start stress corrosion cracking. Brass alloys need internal stresses of only sth. around 10 N/mm² to start the cracking process!

The cracking can proceed relatively slow - within many hours. It can also proceed very very fast - within some seconds to minutes!

And thats the serious danger of brass-made boilers: You can never know, if there's somewhere in it a cracking in process.
You can never know if and when it starts - but when it starts, the boiler will burst suddenly. As the mechanical stresses are most strong in longitudinal direction, this will in general result in a kind of impressive 'explosion' which sets free a high amount of energy.

So, even if many boilers made of brass-alloys work properly, you should as a matter of principle, never construct and build one of brass.

There's a well made, easy to read & understand report about most common types and causes of stress corrosion cracking. Sadly, it's written in german language. Nevertheless, maybe some can read it. There should be enough Articles like that in english language, as it is a common problem everywhere on the world.
http://www.haustec.cc/docs/spannungsrisskorrosion_allertshammer.pdf

Best regards,
Christian