Beading rolled copper tubes

[bryanaverill]

I'm planning on using 5/8 OD x .04" wall copper tubes in a steel shell. I have a tube expander roller. Is it customary to also bead copper tubes? If so, can it be done successfully with a small punch having the required geometry? Does the copper need to be annealed before beading?

The photo is a full scale automatic roller/beader. My roller is tiny compared to this and doesn't have a bead roller.

Words of wisdom much appreciated.

Thanks
Bryan

[derekwarner]

Bryan.......there is a little history with rolling or expanding copper tubes into steel/copper model boilerplates

https://www.modelenginemaker.com/index.php?topic=9556.0

So whilst it is advisable to aneal copper before performing any work processes, I think the inherent differences in lower material strength of the copper to steel would generally preclude copper tube rolling or expanding in lieu of silver soldering

Derek

[cnr6400]

Hi Bryan, some years ago I built a boiler to the Bill Harris 1 1/2" scale steam roller design published in Live Steam magazine in the late 1980's. It used 5/8" OD 1/2" ID  type L copper boiler tubes in a steel shell , with steel tube plates. Bill Harris detailed an expander for these tubes in his design. It used a central screw and heavy steel washers to compress and thus expand a stack of rubber faucet washers to "bulge" the tube slightly on both sides of the tube plates while expanding the tube into the tube plate holes. Very simple, but it worked very well. Annealing the tube was a must, I heated mine to dull red twice before expanding them in. I did have some tubes that weeped a bit at first but after a few sessions of warming the boiler (not to the point of steaming) the weeps stopped. I may not have finished the tube sheet holes nicely enough, or there may have been some scale on the copper. Some pics of test pieces with plate and tube I did with the expander are attached, and include one of the expander as well. Hope this info (based on an actual build) helps. 

[Jasonb]

I've not seen model steel boilers with copper tubes that have been beaded, usually they are just expanded, main thing is to ensure the tubeplate is thick enough so the softer copper does not become too thin when expanded against too narrow an edge

[bryanaverill]

Thanks for the information. This is the expander I intend to use. The hole will be a slip fit. Good point about the hole finish. I will plan on reaming. Tube sheet will be 1/4" mild steel. If beading is unnecessary, I will skip it.

[cnr6400]

Hi Bryan, I didn't do any beading on the boiler I built, just used the expander in my photos, and boiler worked fine. I had propane gas firing on that one, not sure if the tube beading is needed with coal firing or oil firing to help cope with the ash and or soot abrasion using those fuels, just in case you are not firing with gas. 

[Jasonb]

I don't know what regulations apply where you are but for anyone reading this in the UK at the end of the day any queries should be put to whoever is going to inspect and certify the boiler as they will have the final say.

[SandCam]

Hi Guys,

Copper tubes in a mild steel plate will lead to Galvanic corrosion of the steel around the joint.
Steel being Anodic and Copper being Cathodic.

Not really the best combination and may not be permitted by your local regulations.

Just a warning.

Sandy... retired boiler maker.

[Jasonb]

It's quite common on some of the 2" and 3" model traction engines, Haining's designs have been around for years and seem to get approval without problem.

[Zephyrin]

years ago I had changed the flue tubes of a very old vertical steel boiler with copper tubes, expanded in their hole between 2 cone bits and a long threaded rod (no beading); it was successful, pressure tight up to 3 bar, and tested up to 8 bar after caulking with soft solder...
I agree that this fix wouldn't pass the boiler inspector test, but it allows steaming my engine once a year.

the galvanic corrosion occurs with see water, owing to its large amount of sodium chloride, with the low ionic content of the water the steam enthusiasts usually use, this kind of corrosion remains remote I guess !