Staying steel boilers.

[pauldenney]

Dear all

I am looking at designing a steel boiler for the 7 ¼” Marie E I am building at present. Currently I am in the re-search stage. I have just bought a copy of the “Countryman’s steam manual” and in it the author uses screwed stays. Having thought about it I would be concerned that even when welded in a proportion of the thread (in the water space) would be exposed to the penetration of water which would set up corrosion. Given that the book is now quite old is it still current practice to stay a boiler in this manner? On another web site I have seen the stay holes are heavily countersunk and the plain un-threaded stays are welded in place, the weld penetrating all the way to the inside of the plate. I feel the latter method is the way to go what do you all think? I suppose another way would be to loosely thread them and silver solder in place producing a test piece first to check that the solder passes around the threads to the far side of the plate.

Also what’s best steel or copper boiler tubes, welded, expanded or silver soldered in place? If copper won’t the electrolytic imbalance of the steel and copper lead to erosion? In the “Countryman’s steam manual” the author mentions the use of a sacrificial aluminium anode fixed inside the boiler near the fire hole, surely zinc would be better and fixed somewhere it can be periodically changed?

Paul

[jasonb]

Current practice would certainly seem to be a plain rod welded into a suitably preped plate.

Copper tubes can be changed a bit easier than steel and as you don't have to allow for wasting the wall thickness can be less than steel so you can get more tubes into a given space and/or better circulation around them.

I do't think I would want to try and silver solder stays or tubes into a steel boiler, it would need a big heat source to get the steel upto temp to ensure the solder flows right into the joint.

J

[pauldenney]

J

Thanks, Sensable advice. Do you know how mixing copper steel and water effects the life of the boiler?

Paul

[klendo]

Paul,

In our experiance it doesnt, my old chap built a 3" Foden wagon using copper tubes, whilst one or 2 tubes dribbled under hydraulic there that was about it, that engine was made 20 years ago and is still going strong today. Electrolytics were not a problem

I wouldnt overly agree with its easier to get copper tubes out of a steel boiler than steel ones, but then thats only from my experiance. I knopw sounds stupid but just ensure the front tube plate holes are bigger than the firebox end.. Personally I would use expanded tubes over welding them as this makes it much easier to replace should the need arise in the future

Yes there are some published designs which have over looked this fact.