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Butt join copper steam pipes

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steve williams 512/12/2013 22:10:36
1 forum posts


I have never soldered copper pipes together before ( but I have built a steam engine ) , and I'm creating a low pressure flash boiler and need to join some coils of 1/4" OD copper pipe together in series.

Now it makes sense to me to use a sleeve to join the pipes together ( to strengthen the join ) but didnt know if this was essential.

I think temps could be up around 300-400 C when in operation

(1) Should I butt join two pipes without using a joining sleeve

(2) Will silver soldering handle the temps or do I need to use something else?

(3) What type of solder should I use? I assume silver solder but wasnt sure of what % silver i needed in the solder and what type of flux etc?

(4) Do I need to use mapp gas or can a normal butane torch get hot enough for this type of work?

Any thoughts appreciated.....



JasonB13/12/2013 07:40:14
23076 forum posts
2771 photos
1 articles

I would say sleeve the joint, the chance of getting the two pipe ends to stay together with the required gap while trying to solder them are slim. You will also get a far larger area to solder by sleeving so the joint will be better able to withstand the pressure and any physical knocks etc.

You will need silver solder at that temperature 55% and EF Flux The starters pack at the bottom of this page will get you going, also read the "Best practice" on the same site.

For small pipe you should be OK with a butane torch

Edited By JasonB on 13/12/2013 07:46:46

GaryM13/12/2013 09:08:47
314 forum posts
44 photos

Hi Steve,

If you type "silver solder" into the search box at the top right of this page you will get at least 50 threads on the forum discussing problems and techniques related to silver soldering.


Old School13/12/2013 09:30:14
406 forum posts
39 photos


I would not recommend trying to silver solder the coils of a flash boiler together, flash boilers require a lot of heat to work well and the slightest hiccup with the water feed to your boiler you will end up with an series of individual coils or it could happen when you are preheating the coil ready for starting the engine. What you need is a continuous length of copper pipe it is available in coils and I usually get mine from the local caravan supplier they us it for gas pipes.

My straight runner has a copper flash boiler in it fired with a petrol blow lamp it very quickly gets up to temperature and on occasions got to dull red before the water has cooled it. My flash steam hydro has a stainless steel tube boiler and has a brazed joint in it but this is lagged and wrapped in stainless sheet and is routed to the cold end of the boiler. This boiler does get hot for starting it is at least dull red.

Send me a pm if you want a chat about flash boilers



shaun meakin 113/12/2013 10:59:33
60 forum posts
1 photos

Hi Steve, Once again good advice. JasonB refers you to our website, where, as he says, you can find lots of info re joint design, alloy selection etc. if you decide to go down the silver solder route.

All the best, Shaun.

Speedy Builder513/12/2013 12:46:56
2653 forum posts
219 photos

If space is a problem, why not swage one end of the pipe to make the joint. Most 'plumbing' joints in France are made this way to save cost if nothing else. Then braze the joint as suggested.


julian atkins13/12/2013 23:23:51
1258 forum posts
353 photos

for a flash steam boiler i would be inclined to use silverflo 24 silver solder, or sifbronze. sifbronze is what i use on superheater return bends (non-radiant type).



Springbok14/12/2013 10:11:12
879 forum posts
34 photos

Have a look at the CupAlloys web sit

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