Boilers and anodes

[RET]

Hi,

This is what happened with the Boston and Albany tank locomotive (4-6-6) in 3 1/2" gauge. Initially, I made the steam dome, dry pipe cover and all the check valves from brass because I had it and it is easy to machine. After about 2 years of running (not a great lot) I started noticing the signs of dezincification; whitish deposits on the check valves, etc. When I removed a boiler check to see, it was obvious so I ultimately remade all the fittings, including the steam dome and dry pipe cover from bronze (what I should have done in the first place). I have the steam dome and dry pipe cover on display and I don't make brass fittings any more.

I had heard of the dezincification process in brass before, so it was my own fault for not using bronze. I had brass, but I had to go out and buy the appropriate sizes of bronze when I remade everything. I was surprised that it happened so quickly. This is in a copper boiler, not steel.

Just my experience.

Richard Trounce.

[Asteamhead]

Harold,
This discussions regarding stainless steel - you're right to specify the different types of - will never end . Stainless steel is not old school but if treated the correct way, there won't be troubles for a lifetime . Thus I decided to use stainless steel (for boilers) of high quality as 1.4571 (317 Ti) and bronze for fittings exclusively. I regard brass as cheep 'trash' material. Brass (zinc) works as anode, too
An anode made of standard aluminium provided as the easiest method.
But longtime experience showed good lifetime even for brass fittings as long as they are not used in wet ambient. The lower fittings of my water glases were destroyed by zinc-extraction and were to be replaced after a short lifetime. Not those upper fittings in the steam zone, yet .
Even the throttle inside the boiler made of brass still looks fine after some 40 years of use But for new fittings bronze will be the material to be recommend.
After all, a very interesting discussion for corosion can be an enigma
Asteamhead

[Glenn Brooks]

and generally not as strong as carbon steel?

Hmmm. Tensile strength of mild steel is about 85,000 psi, while tensile strength of 302/304 ranges between 75,000/110,000.
316/317, cold finished bars, tensile strength ½" + diameter bars 75,000 minimum.
The above specs according to the EMJ stock book.

Just sayin'

H

Interesting discussion... We would really want to compare SS boiler plate (is there such a thing??) to say 3/8” boiler plate for an actual tensile strength comparisons. Boiler plate and mild steel are different creatures. Then there are all the weldment processes and heat affected zones inside the boiler to consider. Also wondering about what tube/flue material would be used in a Stainless boiler. Asteamhead clearly is way out ahead of most of us when it comes to stainless boilers. So he says it’s workable, Iam a believer. Still, stainless and live steam requires such specialized knowledge. Iam not sure where in the US one could find anybody experienced enuf to take on a stainless boiler, or make repairs.... hard enuf to find a decent steel boiler maker anymore.

Glenn

[milwiron]

Which bronze alloy for fittings do people prefer to use?
In the past I just grabbed anything from a well stocked scrap box at a shop I managed, I don't have that available these days. One of the drawbacks of retirement.

[Steve Goodbody]

Personally, 932 bronze (C932000 /SAE 660). It machines and solders easily and is essentially identical to the cast material referred to in the UK as gunmetal. Cast gunmetal is commonly used in the UK for boiler bushes in copper boilers, for the boiler fittings themselves, for cylinders for smaller models, and for a multitude of other non-ferrous castings.
Best regards
Steve

[Glenn Brooks]

Looks like 964 Aluminium Bronze is also a good choice. I found it more widely available here in the Pacific North West (USA) . Maybe due to proximity to the Alaska marine industry.

anybody have experience with it in boiler work?

Glenn

[Steve Goodbody]

Hi Glenn,
Several years ago I mistakenly bought some aluminum bronze (I can't remember exactly which alloy) instead of 932. It was a bit tougher to machine than the 932, which should have warned me that it wasn't what I thought it was, but I went ahead and made some fittings from it regardless. When I came to silver solder everything together I couldn't get the solder to take at all. I ended up starting again from scratch with 932.

I've since learned (through the good folks on this forum) that you need a different flux to solder Al Bronze, although I can't recall which. My approach has been to keep things simple and stick with 932 which easily solders with the same flux I use for brass, copper and steel.

That said, I still have the Al-bronze barstock, with "Al Bronze - do not solder" notes written in Sharpie all over it, and do occasionally use it. In fact last weekend I made a new boiler mudring washout plug from it, seeing no reason why it wouldn't work just fine for that service in that location.

Best regards
Steve

[Glenn Brooks]

Here is an interesting link discussing dezincification and stress corrosion.

https://donan.com/article/brass-component-failures/

Looks like the big problem with “brass” fittings is using material that has to high a zinc content in the alloy. These OTC hardware variety brass fittings must be made of the cheapest, low grade brass they can find - as opposed to the more suitable brass alloys.

Also, fascinating to do more google research - it appears that appropriate brass alloys for saturated steam valves generally have an ASTM B16 or B62 classification (C8XXX-C9XXX alloys. All of which have a very low percentage of zinc. (4-6%)

http://www.aivinc.com/Assets/cv-301-e.pdf

And, Looks like a quick check to determine if a fittings is an unsuitable brass composition is to determine if the material has > 15% zinc.

Brass fittings with greater than 15% zinc seems to be the alloy that is known to fail rapidly from dezincification.

Glenn

[Asteamhead]

Hello Glenn,
Thanks for your contribution and additional information (links!)!
That limit of 15 % zinc which is recommended for any sort of brass (gunmetal) or low grade bronze seems to be the fazit of this discussion
Here we call that sort of (cheaper) bronze "Rotguss"- Rg. Higher content (82-93 %) of copper, less (2-7 %) zinc and some (4-10 %) tin.
It works fine, too, is easy to machine and to silver solder . Just a little more expensive than brass but a much better choice
Asteamhead

[Soot n' Cinders]

Anybody know what the ratios in McMasters brass fittings are?

[NP317]

From their online catalog, this page:
https://www.mcmaster.com/fasteners/hex-head-screws/
lists the hardware.

If you clip on the part number, you can then click on "Specifications" which , for the bolt I selected, specifies "Silicon Bronze."
Knowing Mc-C, they can probably also provide additional alloy data on request.
RussN