Air leaking by cooper tubes

[lighthousekeeper]

Is their any harm in using a automotive tube expander for exhaust pipes to re-roll my copper tubes? I can pick one up for 50 bucks at NAPPA.

[DetroiTug]

It's two different types of expanders.

The exhaust pipe type expanders (if it's the type you're referring to)use individual blocks that are displaced away from one another by some means - they don't really keep things round.

The roller expanders use three rollers with a tapered pin that works its way in and pushes the roller out as the whole thing rotates. Keep circularity and ensuring a good seal.

Re-rolling a copper tube is an iffy thing to begin with. They are tubes have been overheated and over expanded, and on top of that annealed (soft). I would definitely get the tool for the job. They are around 400 bucks. Might be able to rent one from a boiler shop, or you may even find one that will re roll them for you.

The iffy part of it is when rolling the tube it is being pressed against the opening in the tube sheet, the more it is pressed, the thinner the tube wall is becoming. It gets to a point and it won't seal at all.

How I'd roll that many at once, I'd get a low pressure regulator for air and set it on 5psi and connect it to the boiler, to just maintain some positive pressure. Begin carefully rolling and keep soaping the connection and then it as soon as its sealed - stop and move on to the next one.

-Ron

[Mike Rometer]

Always being up for a good discussion, and playing devil's advocate, it suggests to me that verticle fire tubes are an inherantley poor design as the excess heat in the top of the tubes is effectively trying to destroy the boiler, not boiling water. The ideal must be where the whole of the tubes are under water, did loco engineers get it right?

[cyberbadger]

it suggests to me that verticle fire tubes are an inherantley poor design

Them's fighten words.

They are definitely not the most efficient boiler, but they have had and still have their purposes. They are great where you have the vertical space but don't have the deck space. I wouldn't say it's inherently a poor design - it's a purpose built engineering design that has trade offs.

VFT for life! - Until I get a scotch marine firetube boiler that is...

-CB

[lighthousekeeper]

Just what to let you guys know I picked up a used tube expander off ebay for 50 bucks re-rolled my tubes this afternoon, just fired up boiler took 20 mins to reach 85psi everything appears to be fine now.

Just want to thank all of you folks for pointing me in the right direction once again, my knowledge of steam technology continues to grow!

[RGSP]

This is a bit late, but might just be useful. Many steamboat maintainers in England use Wicksteed type E roller expanders, which cost about £100 (~$130) new, full list price for expanding 1/2" tubes (significantly larger expanders cost more). They are workmanlike tools, and might be worth the hassle and cost of shipping to the US.

[fredrosse]

“You reroll a tube, and then an adjacent tube can decide to cry too.”

That condition indicates too much rolling pressure, distorting the tube sheet holes adjacent to the tube that is being rolled. That much rolling pressure can lead to a permanently distorted tube sheet that will have difficulty from that time onward.

“For reference ASME code boilers can be rolled+bead OR welded.”

Actually, the ASME Code allows “rolled+flaired”, “rolled+beaded” or just straight rolling. The Code also allows seal welding of the rolled tubes, however the use of tubes welded in place without rolling is prohibited.

“Copper is not allowed I believe for ASME code boilers”

The ASME Code does allow Copper tubes the last time I looked. However the Code requirements for Copper tubes usually results in required Copper tube wall thickness significantly greater than available with typical Copper tubing size “K”, which is the thickest wall available for most of us.

“I had my steam mentor use a magmount drill to make the sight glass full length so I could really see and operate at a safer proper level and use the tri-cocks properly. Ross has since fixed the tricock alignment issue, but his glasses are still placed too low.”

The ASME Code directs that the sight glass visible water level can be no lower than 2 inches ABOVE the minimum allowable water level. There has been a lengthy discussion in previous posts on this forum about the merits of this rule.

“Is their any harm in using a automotive tube expander for exhaust pipes to re-roll my copper tubes? I can pick one up for 50 bucks at NAPPA.”

That method is using what is called a “Prosser Expander”, and they are allowed in the ASME Code. However they tend to be far less effective than proper tube expanders (roller type), and are more suited to thicker wall steel boiler tubes.


“verticle fire tubes are an inherantley poor design as the excess heat in the top of the tubes is effectively trying to destroy the boiler, not boiling water. The ideal must be where the whole of the tubes are under water, did loco engineers get it right?”

Submerged tubes are better, because differential expansion issues are greatly reduced. The VFT design is good in that it is simple and cheaper to manufacture, and can provide a small amount of steam superheat. However a VFT will always have more thermal expansion of the firetubes, because the upper tube ends will run significantly hotter than the submerged tube part, and the boiler shell, these elements typically running very close to saturation steam temperature. A VFT with a steel shell, and Copper tube has the differential expansion problem exacerbated by the much greater thermal expansion coefficient of Copper compared to steel.

[TahoeSteam]

Always being up for a good discussion, and playing devil's advocate, it suggests to me that verticle fire tubes are an inherantley poor design as the excess heat in the top of the tubes is effectively trying to destroy the boiler, not boiling water. The ideal must be where the whole of the tubes are under water, did loco engineers get it right?

Simpson Strickland solved that issue with the Kingdon Patent VFT. Tubes were completely submerged. smoke "hood" was the inner shell and there was an outer shell creating a steam space above the top tube sheet... picture something similar to the wet firebox on a VFT, but above the top tube sheet, inner shell tapering to a small chimney outlet

[cyberbadger]

The ASME Code directs that the sight glass visible water level can be no lower than 2 inches ABOVE the minimum allowable water level. There has been a lengthy discussion in previous posts on this forum about the merits of this rule.

Call it what you will but that's raising the minimum allowable water level up 2 inches (Calculation + a fixed 2 inches).

If you can't show the water level then that is not a water level that should ever be reached under any operation.

-CB

[fredrosse]

"Call it what you will but that's raising the minimum allowable water level up 2 inches (Calculation + a fixed 2 inches).

If you can't show the water level then that is not a water level that should ever be reached under any operation."

That is correct, the ASME rules dictate that the sight glass visible level will always assure the two inch margin above the minimum allowable water level, if water is visible in the glass. If water is not visible in the glass, then the boiler is to be treated as a low water emergency condition, fires dropped (shutoff) and feedwater restored after cool down.

It has been suggested that a water level sight glass covering a water level far below the minimum level would be OK, and that the ASME minimum allowable visible point (2 inches above minimum safe level) could be marked on the sight glass. The reason that method is prohibited is because sight glasses are replaced, and the markings might become neglected over the life of the boiler. The boiler operator (present owner, future owner/operator) may then assume the sight glass allows operation near the lower indicated levels, which might be well below the safe operating level. This would be a condition wrought with danger, and the operator continues to cruise along thinking all is OK. All boiler operators should know that if the water level is below the visible portion of the glass, an immediate shutdown is the only option.

Over the years I have often questioned several of the ASME boiler and Pressure Vessel Code rules, and they always have ended up trumping my thoughts of alternate methods in which I superficially decide I know better. After some investigation, the ASME rules always have strong reasoning behind them.