The Steamboating Forum

Always keep the roller clean and well lubricated.
For new installation, a clean and smooth surface where the tube meets the tubesheet is necessary. Clean with Acetone or other completely vol ital solvent before rolling, and be sure oil does not contaminate the rolled joint.

I have the expander in hand. I see how to adjust the penetration depth. I do not know the sheet thickness of this Everett VFT boiler. I will set 1.0" deep. If the sheet is 1/2" then I will be stretching material above the sheet. Is that a problem? My guess is that I will know when i start to squeeze the tube against the sheet. I will know by the torque required. I wont know if i have swedged it enough (except the torque limitation of my arm in the firebox) to close the leak. My guess is that it will be very hard to turn and my swedging will be limited by the strength of my ARM ( singular, one arm) reaching in through the firebox door.
I am going to try tomorrow if I can get the tube ID cleaned well enough.

Any more pointer??

A 1/2' tube sheet would be fairly startling. How big is this boiler anyway!!!

If it's as much as 1/4" I'll be interested to hear. More like 3/16" I suspect.

The ASME Boiler and Pressure Vessel Code, Section 1 - Power Boilers (Any boiler over 15 PSI) has a minimum tubesheet thickness required of 5/16 inch, and many launch sized boilers use 3/8 inch thickness. Anything with more thickness would usually occur with larger commercial boilers, but that is not often the case, the larger designs use stay-bolts and keep the tubesheets relatively thin.

Of course, many steam launch boilers are not designed to the Code, and most hobby boilers, much smaller, use tubesheet thickness far less than 5/16 inch.

When we emulated Fred's boiler, we used 3/8" hot roll plate for the tube sheets and seamless sch 40 ASTM for the shell. It was plenty to roll in to and then seal weld. That boiler has never been fired to this day, only hydro'd. My brother sold it to a guy and he never used it, it's for sale I think.

-Ron

Ron, where, and who, if you could find out I might buy it.

Just something to think about:

I've always bored my tube sheets for a fairly close fit on the tubes. Maybe .002" per inch of tube diameter or even less. All very well until it was time to re-tube and then the scale buildup, however slight, makes it a big hassle to extract the old tube.

I've given a small bit of thought to making the initial fit much looser. Perhaps .01" per inch of tube diameter or more. It would seem to me that the act of rolling the new tube in wouldn't stress the tube excessively. They are, after all, seamless tubes. And when reaming out the end for removal of an aged tube, the reduced diameter of the rest of the tube would make life so much sweeter when sliding it out.

My memories of replacing the occasional tube on a full sized locomotive boiler are that they weren't that tight of a fit anyway. When welding on a new firebox end to an old tube, I don't recall doing a very neat job of dressing down the weld.

Thoughts?

fredrosse wrote: ↑Sun Dec 29, 2019 1:02 am Ron, where, and who, if you could find out I might buy it.

PM sent

Quote: "I've given a small bit of thought to making the initial fit much looser. Perhaps .01" per inch of tube diameter or more."

Not sure I would go that much. I know the Stanley folks are always paranoid about their holes getting stretched too far .. They say they can roll in about three times but I'm not sure how much larger that three rollings results in regards to any sort of dimension. Once the holes are oversized, it's boiler time. On the firetube we built, I reamed the holes 1.25" the same as the OD of the firetubes. We sanded the millshale off the tubes and they fit. And too, the holes were located in a CNC mill, so that helps with alignment issues.

-Ron

I worked for a time at HOLTEC International, they make power plant heat exchangers, and the head of that division told me that a couple thousanths clearance on tubesheet holes is maximum. Rolling reduces the wall thickness of the tubes, and "work hardenes" the tube material, and should be minimized. Yes, much more difficult to extract an old tube, but that is the story I was told.

Typical ASTM A178 boiler tubes are NOT seamless, but I guess there can be seamless tubes procured.

I have often thought of swaging an increased diameter on the tube ends, to allow easier removal, but maybe just a good acid cleaning would do it, just an hour in hydrcloric acid cleans off all scale, leave it much longer and the acid starts to dissolve the bare steel.