Hello All,

The firetubes in condensing Stanleys are,as I understand it, welded into the tubeplates and can therefore be considered as stays. Models which are non condensing seem to often have copper tubes expanded into the tubeplates. These then are surely not considered as stays.
If a steel tubed boiler had its welded tubes removed and replaced with copper expanded tubes would its safe working pressure be reduced ?

Jack.......

My John Goold copper tubed boilers also have steel stays.

Peter

My 21 inch OD John Goold boiler was built for a non-condensing Stanley, Model 607.

The spec is 4 stays and 560 1/2" OD copper tubes at 3/4" grid spacing

So stays are necessary for expanded copper tubes. I assume that the four stays are close to the centre and eliminate four tubes?

Jack.......

Sorry, don't know where the stays are, never looked, but guess they would eliminate 4 tubes.

Jeff, on your 'weekly workshop page' you have a picture of your Brooks ready for a boiler inspection. About 5 tube rows from the outside are a couple of heavier looking tubes, are these hollow stays?

Jack.......

Hi Jack,
To my knowledge the original Brooks boilers were fitted with steel tubes that were welded at the fireplate end and swaged in the smokebox end, Stanley’s were fitted with copper tubes swaged at both ends, each tube acting as a stay in a minor way, but with so many, so closely grouped the overall effect was the same as stays.

It only seems to be the modern way to fit welded stays, when we had the boiler built for the Brooks, six welded stays were specified, this gave all sorts of problems when the boiler was put in service, it would leak very badly whenever it felt like it, we thought this was being caused by uneven expansion between the welded stays and the swaged tubes, so we had the stays removed and very thick walled 1” dia copper tubes fitted with restrictors to the diameter of the normal tubes, (these are the tubes you can see). This cured the problem and I have had 20 years service from it, although it still does odd things occasionally, when it comes to testing the boiler looks much the same as it did when first fitted, all ultrasonic test have shown little or no deteriation.

We have an endoscope which we use to look inside the boiler wherever a fitting hole has been made. In the areas it is possible to look, it looks clean, with no scaling on the boiler wall, the tubes that can be seen are clean, we have found a very fine coating on the bottom of the boiler, inside on the fireplate, it has the consistency of tooth paste and can be washed out to a degree, I have tried various chemicals to shift it, without much luck, these days I check it each time we inspect the boiler, and during each year of use blowdown after each steaming.

To answer your original question, boilers can run at 500 to 600psi with expanded or welded tubes, we test to 1.5 times working pressure plus 10% for the very first test (1000psi) but never more than 1.5. after that, we feel it is possible to damage your boiler if taken higher.

I hope this helps, Jeff.

Thanks Jeff for an interesting reply and the experience with your Brooks boiler.
I would seem that it is ok to use expanded in copper tubes without 'extra' stays.
I had always assumed this to be the case, but in an idle moment I calculated the area of tubeplate,subtracted the area of tube holes then multiplied by boiler pressure....and was surprised at the big number I got !
Thanks,

Jack.......

I'm new to this, in the States, a mechanical engineer, want to build roadable practical solid-fuel capable steam venbicle.

Re: copper tubes as stays, copper has both higher coefficient of thermal expansion, and lower Young's modulus than steel. Thus, in a boiler with a steel shell, copper tubes would be very inefficient as stays. Not to say they wouldn't work, if tubesheets were sufficiently flexible to allow 'bellying' without unacceptably high stresses. Theoretical analysis would be complex, and I'm happy to defer to experience which shows no cracking after many heat-cool load-unload cycles.

What about leaking at tube-sheet joint? Elastic compressive preload of roll-expanded copper-steel interface would tend to be lost as copper is progressively swaged down by its trying to expand more than the hole in the steel tubesheet. Again, experience may prove that the elastic liomit of the copper is not exceeded, and that there is no problem in practice.

Last concern is galvanic corrosion of steel. Spoecial water treatment?

I would very much like to know details of construction of the boiler you describe.

Hi magneticanomaly,

Have a look at these pages on our web site [www.steamcar.net] you can clearly see the method of construction used in the building of Stanley style boilers,

hope this helps, Jeff.