Firetube Boiler Project - Leak Troubles

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Blondihacks
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Re: Firetube Boiler Project - Leak Troubles

Post by Blondihacks »

rkcarguy wrote: Tue Aug 10, 2021 12:43 pm
Blondihacks wrote: Sun Aug 08, 2021 1:47 pm
That's helpful, thank you! I will aim for less clearance next time. People say up to 6 thou is acceptable but that sounded like a crazy amount of open air to me, so I was aiming for 1-3. All the books and articles warn of too little clearance being the death knell, but now I wonder about that advice.
Too tight. We used to shoot for .005" clearance and use a .256" drill for 1/4 tubes. Done properly, you should see some flow through and get a bit of a chamfered build up of solder or brazing rod around the tubes on the **underside** of the tube sheets. On some units which had very thick cast and machined bronze tube "sheets", we used to chamfer the holes about 1/3rd of the thickness deep and then solder/braze them full.
This right here is the challenge with silver soldering boilers- even in a short thread like this one, you literally get opposite advice from different people who all clearly know what they are doing. To me, that says there's a wide range of ways to do it and different people have success with different approaches.
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gwrdriver
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Re: Firetube Boiler Project - Leak Troubles

Post by gwrdriver »

This thread to me seems be getting sillier. OK, so you do a kitchen preheat, then what? How do you handle it and get it to a hearth and get the torches cranked up before it loses enough heat to create oxide and chill the flux? Maybe you have assistants to rush the tube to the hearth and you with torch at the ready? Lucky you, but many of us have to go it alone and often have to devise unorthodox ways of getting the job done.

I don't want to come off as snippy, but I've built over 100 boilers for small scales, 1.5" to 3" diameter. These were mostly straight fire-tube boilers, just as is our subject boiler. I quickly found I needed a way of turning the boilers end-for-end while at temperature which didn't require tongs or anything else which occupied my free hand (or both hands.) Then I watched a video on glass blowing and I had the answer. You ever seen what glass blowers do?

I bolted a short length of 1.5" steel angle to a steel rod so that the "V" was centered and opened away from the rod end and I pressed a short wooden "handle" to the other end. My prepped boilers were bound to the angle by one or two straps of soft iron wire, the type used in construction to bind reinforcing steel, which would withstand what soldering heat they might get without stretching. The whole assembly could be placed on the hearth and rolled to present either end quickly. The wood handle was arranged so that rotation could be made hands-free by using my elbow or hip. I introduced enough friction in the arrangement so that the rod was easily turned but then stayed put where I turned it. End of problem, Zero messed up boilers.

There is no reason such an arrangement couldn't be re-proportioned and quickly made to suit a 4" tube, which would allow the entire boiler to be prepped, heated, and completed in short order without touching it.

I disagree with my old chum John (Baggo) on clearances. In my experience the time and effort put into attempting to achieve less than 1-Thou' clearances in copper are wasted. What I attempt to achieve are fits, in most but not all areas, where the components of the boiler will hold themselves together during soldering without impeding solder flow. However this is never done by tightening clearances. In fact I tend to increase clearances, by relieving and channeling, but I leave small areas of interference sufficient to hold the bits together. The most frequent example of this we read about is center-popping flanged surfaces to create capillary space. There are of course areas where mechanical fastening is necessary as insurance.

In one photo the solder rings around the flues were as pretty and clean as I've ever seen which makes me wonder how could he have such beautiful results in one area and disaster in others? I think maybe there was insufficient relief at the perimeter.
One of the places where I use channeling is at the perimeter of the tube sheet. Initially I'll turn tube plates to a very tight fit to a seat in the shell tube. Then I back off all but say a 10 thou' wide land at the plate edge by 5° or so when assembled will create a V-shaped trough all the way around the plate which reaches almost to the back of the tube plate. When I heat up, the trough fills with flux and solder will flow completely into the full depth and behind the tube plate.

As we all know the solder follows the heat and in the above case I heat the shell to solder the tube plate perimeter. By the time that is achieved enough heat has made its way inward so that the flues usually don't need full-on torch exposure to fall into place. Hope this helps someone.
Last edited by gwrdriver on Tue Aug 10, 2021 1:11 pm, edited 1 time in total.
GWRdriver
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Blondihacks
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Re: Firetube Boiler Project - Leak Troubles

Post by Blondihacks »

gwrdriver wrote: Tue Aug 10, 2021 12:59 pm In one photo the solder rings around the flues were as pretty and clean as I've ever seen which makes me wonder how could he have such beautiful results in one area and disaster in others? I think maybe it's insufficient relief at the perimeter. One of the places where I introduce channeling is at the perimeter of the tube sheet.
"She", actually, but I appreciate the compliment on the initial joints. The ones that look bad are the attempted repairs after the fact. All joints were 1-3 thou clearance, chamfered top and bottom. They all looked good after first heat but a couple of them leaked. My initial reason for coming here was to get advice on how to fix bad tube joints after initial assembly, which I still haven't really gotten a good answer to, unfortunately. Since you're forced to heat from the top (which everyone knows is a no-no because the torch will heat the solder, not the metal) getting a good tube joint repair seems to be very difficult.

People tend to say "make the tubes perfect the first time" which is not helpful advice. I've yet to see a boiler build log of any complexity where someone didn't have to repair a spot or two on a tube, but I haven't seen how anyone actually does that.

In any case, there are many helpful tips in this thread, and I do appreciate everyones' efforts, even if nobody agrees on much about how best to do this. :D
Last edited by Blondihacks on Tue Aug 10, 2021 1:10 pm, edited 1 time in total.
rkcarguy
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Re: Firetube Boiler Project - Leak Troubles

Post by rkcarguy »

Blondihacks wrote: Tue Aug 10, 2021 12:52 pm This right here is the challenge with silver soldering boilers- even in a short thread like this one, you literally get opposite advice from different people who all clearly know what they are doing. To me, that says there's a wide range of ways to do it and different people have success with different approaches.
Indeed, as well as it can vary with solder/brazing rod product used and how much heat is applied. The tube also varied a little and some would be a little small and get small drips of solder down them underneath the tube sheet. We simply made sure they were picked off if they were loose. If you don't get this flow through, the solder joint is only on the surface of the sheet and the protruding ends of the tubes and will quickly fail. The whole process is quite an art, the solder reaches a point where it gets liquid and shiny and starts to flow, and you have to MOVE and apply more, feathering the torch away and then closer to keep the temperature in the sweet spot as you move.
Honestly, because live steam boilers have one end literally in the fire, I'm not a fan of silver soldering at least this hot end tube sheet.
rkcarguy
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Re: Firetube Boiler Project - Leak Troubles

Post by rkcarguy »

rkcarguy wrote: Tue Aug 10, 2021 1:10 pm
Blondihacks wrote: Tue Aug 10, 2021 12:52 pm This right here is the challenge with silver soldering boilers- even in a short thread like this one, you literally get opposite advice from different people who all clearly know what they are doing. To me, that says there's a wide range of ways to do it and different people have success with different approaches.
Indeed, as well as it can vary with solder/brazing rod product used and how much heat is applied. The tube also varied a little and some would be a little small and get small drips of solder down them underneath the tube sheet. We simply made sure they were picked off if they were loose. If you don't get this flow through, the solder joint is only on the surface of the sheet and the protruding ends of the tubes and will quickly fail. The whole process is quite an art, the solder reaches a point where it gets liquid and shiny and starts to flow, and you have to MOVE and apply more, feathering the torch away and then closer to keep the temperature in the sweet spot as you move.
Honestly, because live steam boilers have one end literally in the fire, I'm not a fan of silver soldering at least this hot end tube sheet.
Then, throw in the surface contamination in the form of waxes and oils that come on the material, and you've got a basket case of potential issues.
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gwrdriver
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Re: Firetube Boiler Project - Leak Troubles

Post by gwrdriver »

Blondihacks wrote: Tue Aug 10, 2021 1:09 pm"She", actually, but I appreciate the compliment on the initial joints.
My apologies for not picking up on that, and my responses have admittedly been mostly of suggestions for what to do "next time."
GWRdriver
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Blondihacks
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Re: Firetube Boiler Project - Leak Troubles

Post by Blondihacks »

gwrdriver wrote: Tue Aug 10, 2021 1:16 pm My apologies for not picking up on that, and my responses have admittedly been mostly of suggestions for what to do "next time."
No worries- I get that a lot. :P I appreciate all the "what to do next time" advice immensely, because I will definitely be doing this again, and quite a bit differently.

My primary worry is what I will do if I'm back here in another two months with a leaking tube after first heating and no idea what to do about it. I think my primary strategy will be to solder the tubes to the tube sheets first, as a core assembly, then solder that into the shell afterwards. The tubes will be done with a higher temp silver solder (Harris 56 for the tubes and EasyFlo-equivalent for the shell). This is contrary to the Alex Weiss method, but will allow me to heat the tube joints from underneath, and inspect the joints before assembly.

I suspect it will be difficult to get the heat to the inner tubes, though, because the heat won't make it through the forest of copper to get to the center. Anyone have advice around this? Is it possible or advisable to do the tubes in concentric rings, or should I do them all at once to avoid risk of damage to existing joints?
RET
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Re: Firetube Boiler Project - Leak Troubles

Post by RET »

Hi Blondihacks,

I looked at some of your videos and they are very good and professionally done. There also is a lot of good information from the replies in this thread. Don (CARRDO) and I haven't built a boiler, but we have spent a lot of time working on the Big Boy boiler and in the process, we have learned quite a bit. Our Big Boy thread is now back on page 12. If you want to take the time, it might be worth looking at, especially the part about our silver soldering attempts.

We learned two things about working on a large boiler. Ultimately, what works is using two torches, a large "weed eater" propane torch for the over all heating and a small oxy-acetylene torch with a slightly reducing flame (it is important that the flame is reducing so you don't oxidize the solder or copper) to supply the extra heat required to actually melt the solder where you want it. You can see that the copper sucks the heat away very fast and it takes a long time (about 10 minutes) to get the entire boiler hot enough for silver soldering before even trying to work on it, The wash from the weed eater torch keeps the copper from oxidizing, move that torch away and you can see the oxide form instantly, but moving the wash back over the working area reprotects it again. Make sure you only use the wash from the oxy-acetylene torch, the actual torch flame is way too hot to use. With this combination you have good control of what you are doing. By the way, the black flux is much better; it is almost impossible to burn it, but you can burn the white flux. Once you do that, it doesn't work any more. GWRDRIVER's suggestion about holding and handling a hot boiler is also worth considering seriously.

The second thing we learned is that it is very important to use white insulating firebrick (not regular firebrick) to build as much as you can of an insulating hearth or oven to keep the heat from radiating away from your work piece.

In the replies, I also gleaned some good suggestions. Use dimples on the outside of the tubeplate flange to control the gap so the solder will run where you want it, use steps and tapers to control the joint gap and for large boilers, don't "push," let the part come up to temperature at its own rate. Some of your joint problems may be because the joint may look OK, but the solder may not have fully penetrated through the joint but may be just on the surface. Fully penetrated joints shouldn't fail the way yours seem to. You could use a taper reamer to get a tapered hole for better solder penetration while the smaller end will still locate the tube properly.

In your videos, do the tubes first, then the tube plate periphery later. This way no (or very little) concentrated stress is applied to the individual tubes and collectively, they should be more than able to withstand any stress applied in soldering the tubeplate periphery.

Finally, don't be obsessed by small leaks or weeps, they will seal the first time or two the boiler is used. Again, while it may not be strictly according to Hoyle, a small pump now and then to maintain pressure while doing a pressure test is quite OK. Remember, even with minor leaks, the full test pressure is still being applied to the boiler for the required time. If the boiler is not sound, it will fail catastrophically, usually with a sharp "crack" whether it leaks or not.

Finally, initial testing for a new boiler is usually done at twice operating pressure, but subsequent retests are usually done at 1.5 times operating pressure.

I hope this helps a bit, Don and I are far from being "experts" but we have had some experience.

Richard Trounce.
B&OBob
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Re: Firetube Boiler Project - Leak Troubles

Post by B&OBob »

II have been following this thread from its introduction but was not able until now to make a comment. Without getting into what do do about your current predicament, perhaps a suggestion might help avoid it in the future. I was taken by an ititial statement regarding the rate at which the boiler was initially heated:
I am using the Sievert propane torch that many people recommend (especially Kozo), with both the 1” and 2” tips. It has no difficulty getting the entire boiler up to temperature in a minute or so, so sufficient heat is definitely not a problem.
The issue I have with that technique is the speed with which you heated the boiler. A "minute or so" is entirely too fast to heat a large assembly, as is a 2" Sievert torch too large for a 4" boiler. Using such high heat over a relatively short time might well have changed the composition of your solder alloy, evaporating or "boiling-out" some of the constituents necessary for good flow and a continuous, strong joint. Once that happens, you're finished!

A more desieable technique is to heat the assembly slowly, watch for the silver solder to "flash" around all the joints, and then remove the heat. If you heat the entire assembly slowly and evenly, the "flash" will occur almost simultaneously at all joints. Using an oversize torch for a short time is liable to result in correct flow at some joints but evaporating low temp solder constituents at others, and once that happens, it will be nearly impossible to reheat those foints and re-introduce fresh solder. An indication of that condition is the appearance of overheated solder: it will be porous and "spongy" looking. Additionally, overheated solder alloy will remain "mushy" and will refuse to flow like water like fresh alloy when re-heated.

As others here, I wish you good fortuine in corecting or, at worst, re-doing your boiler!

B&OBob
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NP317
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Re: Firetube Boiler Project - Leak Troubles

Post by NP317 »

I find the above information useful for my future projects.
Thanks for sharing.
RussN
Blondihacks
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Re: Firetube Boiler Project - Leak Troubles

Post by Blondihacks »

B&OBob wrote: Fri Aug 13, 2021 10:19 am The issue I have with that technique is the speed with which you heated the boiler. A "minute or so" is entirely too fast to heat a large assembly, as is a 2" Sievert torch too large for a 4" boiler. Using such high heat over a relatively short time might well have changed the composition of your solder alloy, evaporating or "boiling-out" some of the constituents necessary for good flow and a continuous, strong joint. Once that happens, you're finished!
That's a fair comment based on my characterization, but I oversold that a bit. I should have said "a minute to heat the area being worked on, when the entire boiler is enclosed in pre-heated firebrick". I should clarify as well that while I'm using the 2" tip, I'm only using about 1/4 of full gas pressure. The big tip is nice for very even heating, but it doesn't take nearly the full capacity of that monster to heat the joints. It's a very efficient setup, but doesn't show any signs of excessively fast heating, I don't think (until I went nuclear trying to repair it, anyway) . The solder flows very well, leaving shiny joints when I remove the heat.

I thought the folks in here might be interested in the autopsy. I did end up cutting the boiler apart, and what I found was interesting.

The joints on the underside of the tubes were very good at some point in their life. You can see I got excellent penetration and a nice fillet on the backs of all of them. Surprisingly good considering most of the heating was done from above, against recommended practice:

Image

However, looking closely, you can see what went wrong- in the middle of that perfect-looking joint is a crack. Almost all the tube joints show these cracks. I think that damage to the joints was done in my subsequent leak fixing attempts. It's hard to say the exact cause- overheating, differential heating, cooling too fast, too many heatings, or some combination of the above. However with those cracks on the undersides of the joints, these were not fixable. There was a distinct turning point in my repair efforts where things went from "improving slowly" to "worsening quickly" and I presume that's when these cracks happened.

The other end is the same story. Note that I got poor penetration on that one boiler bushing, and it was a constant leaker, so that was also probably doomed from the start. I should have chamfered the underside so silver solder had a way to get in (and next time I will heat from below, regardless).

Image

The shell joints looked very good (hard to see past the copper carnage in the photo), but that's not surprising since those joints are comparatively easy.

Image

None of this copper will go to waste. While it's all too distorted from repair attempts and the "prejudicial deconstruction", it's all usable for something else. I'll split the shell, anneal it, and unroll it to make a nice big piece of copper plate. It's way too out-of-round to try and turn or mill out the debris and reuse it for a shell. The tubes will never be tubes again, but will go on to live productive lives as shim stock, soft jaws, or other things.

My plan for the redo is:

1) 15 1/2" tubes in place of 26 3/8" tubes. This is only a 30% loss of surface area (still fine for my engine) and will be a dramatically simpler geometry to build
2) I'll do the "core" first, soldering the tubes to the tube sheets, applying heat from the "inside" of the joints. I can then inspect and repair before moving on. I may even try to rig up a tube to pressure test the core by itself before moving on (with big O-rings, perhaps). I will use higher temp silver solder for the tubes.
3) The core will then be soldered into the shell with lower temp solder. The outer shell joints are trivial to repair if something goes wrong, so I'm not worried about this part at all.

Thanks for your input and support, everyone. It's greatly appreciated and I feel good about my chances on the next attempt. The autopsy photos show, if nothing else, how close I actually got to a good boiler! In the end though, I feel good about the decision to cut it apart and start over.
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SteveR
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Re: Firetube Boiler Project - Leak Troubles

Post by SteveR »

Interesting results - thanks for sharing. BTW - in your first post you mentioned that:
This is my second boiler. The first was a 4” pot boiler with a handful of fittings in the shell, and it was challenging, but I got it done.
Were the problems you encountered the first time the same or similar to those on the the second?
And what brand of solder and flux are you using?

Thanks,
SteveR
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