Firetube Boiler Project - Leak Troubles

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Blondihacks
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Re: Firetube Boiler Project - Leak Troubles

Post by Blondihacks »

baggo wrote: Sun Aug 08, 2021 11:46 am When I was watching your video on fitting the boiler tubes and end plates I was thinking 'that's an awful lot of clearance for the solder'. Personally, I would never use the recommended clearances as I think they are far too big. So long as the tubes etc. are a sliding fit into the respective hole then the solder will penetrate the joint with no problems. The thicker the solder in the joint then the more prone it will be to crack due to differential cooling. Also some solders are not very good at gap filling. I've no experience of the Harris solders though as in the UK we tend to use Johnson Matthey or Cup Alloys solders.
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.
baggo wrote: Sun Aug 08, 2021 11:46 am Have you tried wrapping the outside of the boiler with a thermal blanket to stop it cooling down so quickly after the soldering? (Wrap it around the boiler before soldering). That may help to prevent cracking of the joints due to too rapid cooling.
I did indeed. I kept it in the hearth and wrapped up to cool it as slowly as possible, just in case.
baggo wrote: Sun Aug 08, 2021 11:46 am If you do have to start again (and I hope that you don't) consider soldering in the bushes first with a higher melting point solder. Those joints then shouldn't be affected by the subsequent heating to do the rest with your 56% solder.
The bushings were actually okay- they seemed to be far enough away, down on the middle of shell, that I had no trouble with them leaking or needing multiple repairs.
baggo wrote: Sun Aug 08, 2021 11:46 am There is another way to seal the leaks but ONLY if the boiler is structurally sound. That is to caulk the leaks with a high melting point soft solder such as Comsol. That melts at about 305°C so won't involve reheating the boiler to such a high temperature. It does tend to be frowned upon over here nowadays by some people (usually those that have never built a boiler) but it's a perfectly safe and valid way to fix a leak (in my opinion anyway). You do then have to be more careful about the water level in the boiler and not let it get too low.
Yah, I did actually do that for one stubborn leak on my previous boiler, but I really wanted to do this one the "right" way. Here's what I get for that! My last hail mary will likely be to swage the tubes real firmly then reflow solder one more time to caulk. I know swaging-and-caulking is also frowned upon these days, but at least it would be silver-solder caulking.
baggo wrote: Sun Aug 08, 2021 11:46 am Don't give up and good luck with it.
Thank you! The encouraging words I've gotten from people really do help. You advice is greatly appreciated also.
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JBodenmann
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Re: Firetube Boiler Project - Leak Troubles

Post by JBodenmann »

Hello My Friends
Hi Quinn, I have enjoyed your videos. Your boiler and tubes are most likely structurally sound at this point, so I would give stay bright solder a try. It isn't necessary to re melt the silver solder to do this so you aren't likely to cause more leaks. Stay bright melts at a lower temp than full on silver solder, although it is marketed as silver solder. As this is the cool end of the boiler that won't be a problem. I have used this to fix leaks on copper boilers in the past and it works just fine. Probably not a good idea inside a fire box. In the bad old days they built boilers with soft solder and rivets. The rivets for strength, the soft solder for sealing things up.
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Bill Shields
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Re: Firetube Boiler Project - Leak Troubles

Post by Bill Shields »

Are the tubes a tight fit in the sheets? You need a little gap to get the solder to flow.

I would take a dremel and grind away the solder in the leaking areas. Reflux and resolder.

Heat with multiple sievert torches and or put in charcoal to get uniformly hot almost to soldering temp.

Kick in areas being resoldered with a feathery oxygen torch. Heat id of tubes with torch to get solder to melt.

Allow to cool slowly.
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GregE
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Re: Firetube Boiler Project - Leak Troubles

Post by GregE »

Hi Quinn,
Sorry to hear of your struggles- I've also been following your boiler build videos- nice work!
I completed my Kozo designed boiler for the K-27 locomotive last spring, and I built the A3 locomotive boiler a number of years ago.
One trick he discusses that I DIDN'T do on the small boiler, but did on the large one was pack the flues with ceramic cloth/yarn part way down to reduce the heat transfer expansion, and consequent contraction on cooling. I had an awful time on the little boiler chasing leaks from one end to the other. The idea being that being less massive, they expand more than the boiler shell and the joint can't withstand the force on cooling and cracks.
I was able to get the large boiler soldered tight with the exception of a couple weeps the sealed up after a tappy-tap-tap with a punch.
Best of luck- I can feel the pain looking at your photos!
Greg
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SteveR
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Re: Firetube Boiler Project - Leak Troubles

Post by SteveR »

As you already mentioned, you need to figure out what the root cause of the failures are before you try to fix this one again or make a new one.

I would call your solder and flux vendors and ask to speak to an applications engineer. This is what they do.

From the Harris website:https://www.harrisproductsgroup.com/en/ ... oints.aspx

If the filler metal cracks after it solidifies:
When brazing dissimilar metals, the different coefficient of expansion may put the filler metal in tension just below the liquidus temperature during cooling. This sometimes occurs in a copper-into-steel joint. The copper expands and contracts at a greater rate than the steel. Brazing alloys are stronger in compression, so a steel-into-copper assembly would help alleviate the problem.
Brazing steel (or other ferrous metals) with an alloy containing phosphorus can lead to formation of a brittle phosphide prone to cracking. Braze ferrous metals with non-phosphorus content alloys.
Excessive joint clearance can lead to filler metals cracking under stress or vibration. Make sure clearances are held to .002” - .006” at brazing temperature (depending on alloy).
Too rapid quenching can sometime cause cracking. Let joint cool more before washing off flux residue.

If joint leaks in service:
90% of “leakers” are due to incorrect brazing technique. The most common causes are:

Improper (uneven) heating of joint. The effect of this is inadequate or incomplete penetration by the filler metal. Review proper brazing technique.
Over heating, causing volitalization of elements (phosphorus, zinc, etc.)
Incorrect torch flame adjustment leading to deposition of carbon or causing excessive oxidation.


My 2 cents: Propane torch is too hot, which makes metals expand too much. Rinse better after pickling.

To practice, take a flat sheet with a bunch of holes and solder tube ends in it. Use this instead of experimenting with your boiler.

Good luck and let us know how it comes out.

SteveR
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Bill Shields
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Re: Firetube Boiler Project - Leak Troubles

Post by Bill Shields »

also, when building this type of boiler, I solder the tube sheets to the tubes -> then solder the lot to the outer shell...
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rkcarguy
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Re: Firetube Boiler Project - Leak Troubles

Post by rkcarguy »

I used to work in an exchanger place for marine cooling units, they were all copper just like your unit shown here.
We brazed the tubes into the tube sheets, then the core was brazed into the shell but using a high silver content rod with a lower melting temperature so the brazed tubes weren't affected. Then, any repairs to fix leaks (which were rare) were made with silver solder. We would grind a little pocket at the leak area with a Dremel and give it quick shot with the torch and silver solder. The general idea is that you use a lower temperature product at each subsequent operation, so that it doesn't affect those prior.
We used white flux for most everything, but some brazing rod seemed to perform better with the black.
Do not quench, let everything air cool or you chance getting cracks.
Last edited by rkcarguy on Tue Aug 10, 2021 12:27 pm, edited 1 time in total.
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NP317
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Re: Firetube Boiler Project - Leak Troubles

Post by NP317 »

Pictures do not show up for me.
Just little boxes with a "?" inside.
Sigh.
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Gra2472
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Re: Firetube Boiler Project - Leak Troubles

Post by Gra2472 »

I had a project similar to this a few years ago. I ended up putting the whole thing in the oven and heating it slowly until the solder melted. Then I turned off the oven, apologized to my wife at the time (different life) and went to the bar while the whole thing cooled down. It wasn’t nearly as large as your boiler, but it worked. Before scrapping the whole thing, I would say clean it as best you can and try putting it in the oven. Just heat it slowly so that everything reaches the right temperature at the same time.
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Bill Shields
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Re: Firetube Boiler Project - Leak Troubles

Post by Bill Shields »

Oven hot enough to melt elver solder?
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Gra2472
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Re: Firetube Boiler Project - Leak Troubles

Post by Gra2472 »

That's a good point, I didn't take into account the silver solder. My project was an experimental heat exchanger for my home brewery. I used copper pipe fittings, and plumbing solder which does melt in the oven. But preheating might help in this application. Just a thought.
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rkcarguy
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Re: Firetube Boiler Project - Leak Troubles

Post by rkcarguy »

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.
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