The Steamboating Forum

Like Red Green making his own pacemaker, he's clangin and bangin away, he stops and looks up at the camera holding a piece of wire in each hand and says "Now, I will attach these two leads....to my heart''. I miss that guy.

Comming back on the water tube boiler, we have discovered that each tube is surrounded by a thin-walled copper bushing in the tube sheet.

Any idea what could be the reason for such a design?

The holes are reamed together, so the reason is not to even out any angle deviation between the two holes

Maybe to act as a seal but also a 'bearing' allowing for thermal expansion of the tubes?

The copper bushing, I assume this is a short piece of copper tube, matching the steel watertube outside diameter, and matching the larger tubesheet hole diameter. This might allow far easier watertube removal, as the copper bushings could be sacrificed, then watertube external corrosion/scale will not interfere with tube removal, they can slide out without collapsing the entire watertube.

Has anyone on the forum seen this arrangement previously?

Years ago there was a boat shop down the road from us that had the boiler from an old Case portable engine to supply the steam box. When it came time to replace some of the tubes, the owner showed me some copper sleeves that just slipped over the tube ends rolled in on one end so as not to slide on in past the end. He said that the tube supplier indicated that they were to be used as bushings in the case of an over sized hole in the tube sheet, so I remember.

Dave

Quote Has anyone on the forum seen this arrangement previously?

Not that, but the Stanley boilers use a small steel ferrule/swadge inside the end of each firetube to keep them expanded.

I'm thinking you're right this is a small sacrificial sleeve to make retubing the boiler easier and help seal. Copper seals and gaskets are common as they are soft and will conform to irregular surfaces rather than steel to steel. probably not a bad idea. Sounds like a lengthy lathe job is necessary.

-Ron

"Has anyone on the forum seen this arrangement previously?"

Yes. I have found those copper sleeves in full-sized logging locomotives, on the 2" OD boiler tubes.
They facilitated sealing when rolling tubes into worn tube sheets with enlarged flue holes.
Probably had other reasons for use, but not in my experience or knowledge.
RussN

Thanks for all your comments.
We will discuss with the boiler owner how he prefer the job done - with or without copper sleeves.
Under all circumstances we intend to fabricate a big blind flange to fit the bottom of the firebox.
In this manner we can pressure test the new tubes, by water filling the box, before the whole boiler is bolted together.
If we make the test after reassembling the boiler, it is impossible to locate leaks and re-expand the leaking tube.

Testing the boiler by pressurizing the tubes with external pressure will introduce forces tending to expand the furnace/stack, as well as pushing all the tubesheet joints away from each other, the reverse of normal pressure loading. Difficult to determine if this might lead to overstress and potential deformation without much technical details, which are probably not available.

It is recommended that only moderate pressure be used to test the tube repairs with the furnace/combustion gas path internal pressure scheme. After the boiler is assembled in its functioning configuration, then hydro static test it to 150% of maximum allowable pressure, filled with liquid water only.

Hi
Why do you think that the tube sheets will deform more when pressurised from the inside of the gas path?
The force will be the same as if pressurised from outside, hold in position by the tubes.
The longitudinal forces on the tubes will be pull in stead of trust, but that should not worsen anything.