Copper pipe couplings combined to maka a boiler - would it work ?

[arnoldb]

I'm looking at building a boiler based on Sandy's 3" horizontal to occasionally run my models on steam.

All attempts to source a short piece of copper pipe suitable for this have been fruitless; I can buy a 6 meter length here in Windhoek, but that is way out of my budget and I don't think I'll build enough boilers to ever use it up.

What I can get easily, is copper couplings used to join copper pipe in the various diameters, and at a more budget-friendly price. Problem is, these are too short to build a boiler from.

So I'm thinking of taking two of these pipe couplings, and with a strip of copper plate made into a fairly close-fitting ring to fit the ID of the couplings (or even a ring sawn off from excess length of one of the couplings and split and trimmed to fit inside), riveting the strip to the two pipe couplings together, and then silver brazing the joint thoroughly.

I've not seen this done anywhere. From my limited experience and point of view, this seems a viable solution - so the question is, can any of the more experienced boiler makers give some advise on trying this? - Any input/criticism is welcome!

Stays are also a problem; I can't source copper rod, and while I could use bronze brazing rod, I'm not sure of the metal composition, so I'll stay away from that. Would stainless steel work for stays ? - I know I can silver braze that to copper.

I'm happy to buy a full 6m length of the thinner copper pipe needed for the flues, as it has other uses for me as well.

I'm looking at a max 35 psi operating pressure, and have the kit needed to thoroughly pressure test the boiler to twice maximum (or even up to 200 psi). I cant find boiler regulations for small boilers here in Namibia - and government officials in the relevant ministry just cloud over when I ask them about this, so I'll happily stick to one of the established US / UK / Australian codes - I like my body the way it is, and do not wish to harm to anybody around me either.

Regards, Arnold

 

[Jasonb]

Personally I would avoid any form of "plumbing" copper as it can contain lead, this lead can affect the strength of the silver solder as the heat of soldering can make it leach out of the copper and into the solder.

Also you should be looking for oxygen free or de-oxygenized copper as the soldering process can weaken this copper containing oxygen particularly if use oxy-acetylene.

Jason

 

[kf2qd]

I would think that the problem would be the number of joints you would have to silver solder/copper braze would quickly make the one piece tube seem a lot less expensive.

Another point - you would be heating this unit and creating presurized steam and I would think that instead of trying to cheap your way into a boiler you would want to follow standard practices because safety really trumps cheap in this application. A failure in even a small boiler releases large amounts of energy very rapidly and the probability of injury goes up proportionally to the square of the corners cut.

Compressed air has the advantage that it tends to be cooler, dryer and a bit safer thatn steam. If you want to cut corners then use compressed air and not worry about the expense of steam.

 

[SBWHART]

Arnold

Can you get hold of copper sheet say 2mm thick you can roll this into a tube and join it with a lap joint or a strip on the inside. You will only need to stay the end plates, I'm not familiar with the type of boiler you want to build but if its the type with the chimney up the middle these are not usually stayed.

Hope this helps

Stew

 

[GWRdriver]

I would avoid any form of "plumbing" copper as it can contain lead,

This is not true. In the USA, alloy C-122 copper (common water pipe) contains only copper and a trace of phosphorus (.2%) and, along with C-110 sheet which has the same composition, provided one uses a seamless hard-drawn tube of adequate wall thickness C-122 tube or pipe is perfectly suitable for model boilers.

you should be looking for oxygen free or de-oxygenized copper

This is not true either. Deoxygenated copper is primarily used in electrical equipment and is of no benefit for boilers and is harder to find thus will be more expensive. There are some welding applications where deoxygenated copper is needed but not for small models.

I agree whole-heartedly that boilers should not be backed into on the cheap, but 35psi is not a great deal of pressure to deal with, provided of course that you do the right thing with the materials and limit your pressure to that, or at least under 60psi. Often in the manufacturing wrought copper fittings swaging and punching introduces potential weak spots in the fittings which are fine when presented with household water temps and pressures but could turn into problems if subjected to steaming pressures and temperatures, above say 60psi. A copper coupling could make what you need, provided the wall thickness was adequate, which for 35-50psi should in no case be less than 16ga or 062" and I would go at least one step thicker at .072"-.075" or thereabouts. If a swaged coupling/fitting is used I would also look for and prepare to fill or flow over any manufacturing marks or deformations with silver solder.

I would avoid stainless in any model boiler and for staying (center stay?) for what you propose I see no reason why a length of bronze welding rod of any alloy would not work, I've used it myself a number of times. Another option would be a piece of heavy copper wire, of the size used for grounding electrical systems. The problem with the copper rod is that it sometimes "slacks" during the silver soldering process so that there is then no tension in the rod between the heads which would then allow the heads to deform considerably under an extreme over-pressure condition. In larger locomotive boilers I make arrangements for one end of each longitudinal stay (always alloy C-510 phosphor bronze) to have a threaded "take-up" connection so that all the stays can be tensioned after silver soldering. That would be over-kill for your boiler. What would be a better solution is to silver solder one end of the stay in place and leave the other end threaded and nutted and after tensioning simply caulk (seal) the nutted end with soft solder. This would do just fine for your application, although as has been pointed out, if you use several flues you won't need longitudinal stays.
,

 

[johnthomp]

rather than back plate the fittings together id try and flange the ends of the fittings to slot inside each other then rivet together saveing a lot of effort but gaining near enough the same look but less likely sources of leakage
hope this helps
reguards john

 

[arnoldb]

Many thanks for the prompt responses Gents!

Jason, I neglected to mention that this is the copper fittings used in Air conditioning and Refrigeration installations - and, visually at least, looks of a much better standard than those used in plumbing, and are definitely silver brazed here all the time.

kf2qd - thanks your concerns are noted. It will only require one joint connecting the two couplings, so at max one silver brazing stick extra.

Stew, thank you. I did consider that, but it seems to me that making one long seam might be more error-prone than the circular one. I have some 2mm copper plate, but would rather use that for the end caps - finding plate is as hard as pipe. It's a horizontal boiler (like the one in firebird's new Beam engine build), so 2 flues at the bottom and a couple of stays at the top.

Harry, many thanks! The fittings I can get is 2mm (.078") thick, so that should be adequate. Also very clean; there are not manufacturer's markings on them, only three small indentations spaced around the the center of each to limit pipe travel when joining pipes - these I can easily fill up with silver solder.
And thanks for the heads-up on the stays; when I make the boiler, I'll silver solder the firebox side and thread and caulk the smokebox side. I dont even need 35psi from the boiler; all of my engines runs happily at much less than 10psi; I settled on 35 for "just in case" for future projects.

Thanks John - I'd prefer not to play around with flaring and shrinking for a joint like this, as I'm not sure how the flaring/shrinking will affect the strengths in the affected areas, especially once its heated up and under pressure. Having a backing ring in the joint would make a much stronger joint from my point of view.

Once again, thank you all for your responses.

Kind regards, Arnold

 

[bearcar1]

Arnold, I sent you a PM but apparently you have not seen it yet (I miss them quite a few times due to not looking/seeing that teensy tiny little 'plus' sign next to messges). Anyway, let me know what you think about that and PM me back.

Cheers

BC1
Jim

 

[arnoldb]

Thanks Jim, I was PM'ing while you posted ;D

Kind regards, Arnold

 

[GailInNM]

Arnold,
The practice of using a silver brazed coupler ring to join two sections of a boiler in the manner your are proposing is a standard practice when making small wagon top boilers. A wagon top boiler has two differing diameters of boiler section connected by a tapered section arranged so the bottom of the boiler is a straight line and the top steps up in height going towards the firebox end. The tapered section is most often rolled from copper sheet with a lap joint seam. Yours would be simpler as there would be no angles involved. If the joining ring is a good fit then it will not take much silver braze material.

Kozo details a procedure for doing this in his book "Building the Climax".
Gail in NM

 

[mklotz]

... I sent you a PM but apparently you have not seen it yet (I miss them quite a few times due to not looking/seeing that teensy tiny little 'plus' sign next to messges).

Bearcar,

Are you aware that you can set your forum preferences such that you receive an email notification whenever you receive a new PM?

 

[bearcar1]

Thanks Marv, and yes I finally have gotten that straightened out. Teensy tiny little plus sign you know? Very small. These old eyeballs do not see those types of things like they used to ya' know? 8) ;D

BC1
Jim

 

[tel]

How long a bit do you need Arnold ?- shouldn't break the bank to get a bit to you.

 

[arnoldb]

Thank you Gail. I didn't even know about the wagon top boilers! - some research required!. Kozo's name pops up frequently in relation to boilers and locomotives, so I think its time I ordered one of his books - it appears that there is a wealth of information in them!

Tel, thank you for the offer :bow: - I had a similar one from Jim :bow:; this forum is "haunted" by great blokes!

I think more of an explanation is in order...
I'm trying to use locally sourced material as much as possible. There are a couple of reasons for this - besides myself being a proud and pig-headed idiot individual :.
The simple models I've built so far have raised an unexpectedly high level of interest amongst the local people who have seen them, and the #1 question is "Where do you get the materials to build it ?".

I want to actively promote model engineering as a hobby locally - hopefully to set up a Namibian club, and I want to get some more models built to set up a display at at our annual veteran car show, as well as at the local RC car and airplane gatherings. If I can show truthfully that my models were built with locally available material, this might entice more people to give it a try. If I can get a club set up, sourcing material will be easier, as the members can then join together to share in buying full lengths and dividing up according to needs.

Sourcing locally has also brought additional benefits. When I started with this hobby, I was treated like cr@p in most of the places I tried to get tools and material from - this was often reflected in the price I had to pay. Regular visits to buy small bits and bobs and a bit of a show 'n tell by taking one of my builds along started to break down barriers, and I now regularly get a hearty welcome and a bit of discount on the bill - sometimes even free bits! I'd like to be able to pass that privilege on to other potential local model engineers.

And a sudden unexpected turn of events...
I've had to save up to buy material and tooling to fuel the hobby for the most part. That might change for a while....
Today was one of those rare GREAT days! I received a MUCH better milling vise (Thanks Wagner!) and a set of boring bars I've been waiting for. To crown the day, the salary officer of the company I work for came into my office and handed me my pay slip - prematurely! We use folded and sealed pay slips at my workplace, and this one was thicker than normal... Sealed inside was a letter from my financial director stating some facts about the company having a hard time with the economic down-turn and so on. I know that!... I've busted my chops for my workplace for close on 10 years, and things were not looking great this year, so imagine my surprise when the end of the letter from the FD terminated with "...to reward you for your effort, we have decided to increase your salary to ..." and the difference between my old and new one could buy the original 6m length of 75mm copper pipe, with some to spare ;D This opens up a new lot of possibilities; I can buy the tubing I need and keep it in stock, and in turn help out others if I can, just like I've been offered to!

Kind regards, Arnold

 

[steamboatmodel]

That is great news Arnold, Its nice to hear that some companies do appreciate hard work and dedication.
Regards,
Gerald.

 

[njl]

Congratulations Arnold glad things are looking up. Hope you can get your engineering club of the ground too.

Nick

 

[bearcar1]

I'm sure the attention to detail in your machine work also gets reflected in the work work that you perform on a daily basis 'in the real world'. This trait has obviously captured the eyes of those in charge and rightfully so on their part rewarded you accordingly. More companies should follow that approach rather than worrying so much about the bottom line, of course the same can't be said for US banking institutions. Anyway, my hope is that all of your efforts to promote this hobby will catch on, maybe not all at once mind you but if one other person gets going it can have a very positive effect and before too long a small group has formed. We are always available for any type of support you and hopefully your as yet to be formed group will need.

BC1
Jim

 

[arnoldb]

Thanks Gerald... Yes, it is nice to find surprises like this!

Thanks for the good wishes Nick!

Jim, thank you for the kind words; yes; I'm very fussy about and proud of the IT infrastructure I administer. Must be the German blood of my ancestors showing through ;D. And yes, as/when I find people interested in ME, I'll introduce them to HMEM! :-X I won't expand on the banking systems!

Regards, Arnold

 

[doubletop]

All attempts to source a short piece of copper pipe suitable for this have been fruitless; I can buy a 6 meter length here in Windhoek, but that is way out of my budget and I don't think I'll build enough boilers to ever use it up.

Regards, Arnold

I had the same problem and took the view that if they stock it somebody buys it so asked the supplier who bought their stuff. He gave me the name of some of the companies who purchased from them. I rang around to see if they had any offcuts. None of them did but one told me which scrap yard they took the offcuts to and went there, and they had some.

I found the best time to go to the scarp yard is around 5:00pm on Friday. Its just a stream of trades people cashing up on their scrap, no doubt for the beer money for the weekend. I was the only one leaving with copper.

1 meter from the supplier $250, Scrap $12/kilo or thereabouts. I think I got about a meter or so for $80

Pete

 

[xo18thfa]

I don't think there would be any problem using couplers soldered together with a strap inside as a joint. Kozo Hiraoka has built some very complicated boilers for his 3.5" gauge steamers using strap at the joints.

The leaching problem mentioned earlier really concerns zinc. Zinc can leach out of brass, potentially leaving it brittle. That is why brass is not used in boiler construction, only bronze.

Harry Wade mentioned Phosphor Bronze Alloy 510, which is the most widely used. I have used Alloy 544 (easier to machine version of 510) and 932. They have run strong and solid for many years.

I would stay away from stainless too. Stainless can get a mind of its own sometimes when trying to solder it. Go with a bronze stay, it is so much more reliable to solder. Silver soldered flues act as stays too, you may not need a stay.

As a matter of safety and professional practice, pressure test your new boilers to twice operating pressure with all the bushes plugged. Once a year thereafter, test to 1.5 operating pressure with all the fittings in place. If there is ever a problem, they will turn up at test time.