Firetube Boiler Project - Leak Troubles

[Greg_Lewis]

Sandiapaul:
I find that the black flux works over a larger temperature range, stays active longer, and is easier to get off when cool than the white. If the white works for you, there is no reason to change, but I had lots of trouble with it.

[Blondihacks]

More of a question than advice, but with this instance of the small vertical boiler, wouldn't the low melt point 45 silver solder better suited ?

I’m using the lowest melt-point silver solder that I can get. See above for my new plan on that point. The Harris 56 is about 1145-1205°F

[gwrdriver]

Greg,
Do you mean the black flux for boilers specifically? I've been using the white flux for decades with no issues, but I've never done a boiler.

That's my experience also, but then amateur skill and equipment vary greatly. Have there been instances when I needed my flux to stay active longer? Of course, but that was before black flux became our savior and we dealt with what we had.
My understanding is that black flux was developed for use in industrial oven-brazing, where fluxed and soldered parts took a long conveyor ride through an oven and the flux needed to remain active for most of the trip.

Also, for anyone planning to throw their white flux in a dumpster, let's keep it out of the land-fills. Please box it up and send it to me. I'll dispose of it in an approved manner.

[Bill Shields]

keep the white for small parts

[Builder01]

I use both kinds. I discovered the black after using the white. I mostly use the black, it is a "tougher" flux. Seems to last longer under heat than the white. This seems for my work, advantageous for large assemblies. I did my entire copper loco boiler with black flux. 5" diameter by 19" long. Passed it's 1st hydro in 2017.

[RET]

Hi everyone,

Something new to think of. My mentor, Harry Hawkins suggested that one of the things to do is to keep a supply of 1/16th dia. brass wire to use when silver soldering if you wanted the joint to be a bit stronger (I have some, but I haven't tried it yet). You added a little bit of the wire to the melted solder at the joint to form an alloy that would raise the solder melting point and increase its strength because in a sense you would be "brazing" the joint.

Now I haven't tried this myself, and I'm sure that Harry was using the old cadmium style silver solder, but for those of you who are venturesome and who may also need more strength, it might be something to try. If you do, let us know if it works.

Richard Trounce.

[Blondihacks]

My mentor, Harry Hawkins suggested that one of the things to do is to keep a supply of 1/16th dia. brass wire to use when silver soldering if you wanted the joint to be a bit stronger (I have some, but I haven't tried it yet). You added a little bit of the wire to the melted solder at the joint to form an alloy that would raise the solder melting point and increase its strength because in a sense you would be "brazing" the joint.

Mr. Watanabe demonstrates something similar, using brass wire to do a very high temperature braze on the superheater on his William locomotive. Very interesting and not something I would have thought doable with such basic equipment. He said it was not easy and the joints have to be small and very simple for such a high temperature process to succeed with a basic torch, but he did it. He arranged the superheater plumbing such that he only needed one of these joints and the geometry is very simple. It looks much more achievable for the average hobbyist than getting a gas-tight stainless weld, which is the usual recommendation.

http://livesteam.sakura.ne.jp/eW-superheater.htm

[SteveR]

I'm having difficulty coming up with a mechanism where the flux (either type) creates cracking in the middle of the solder joint as the pictures have shown. I would think a flux problem would cause poor wetting and maybe a crack at the solder-copper interface - which I have not seen here. (BH - any apparent?)

I think of cracks as resulting from stress. Stress can be caused by heating and cooling and differential shrinkage.

I wouldn't change flux types just yet; you're already going to assemble it differently. Let's see how that comes out.

SteveR

[Blondihacks]

I don't think the implication of the above thread was that flux type was the cause of the original issues. It was just being suggested that the black flux is easier to use so I should try it next time. The issue of the joints cracking is still somewhat unknown, though overheating or excessive differential heating seem likely.

[RET]

Hi Blondihacks,

You talked about a stainless gas tight weld. Here is what we did for the Big Boy superheater and for the Boston and Albany (3 tubes in that, but they only extend 1.5" into the firebox - needs to be more). In both locomotives,the stainless tube is just over 1/4" OD. and just under 1/4" ID. You have to bend the tubing ends first, bevel the ends, then get the ends TIG welded with stainless rod. You have to have the angle for TIG as shown in the left hand pair, if you don't the arc doesn't go where you want it to and the inside of the joint won't be gas tight. As you may have guessed, I found all this out the hard way.

Steps in making Big Boy superheaters.

Once the weld has been done, you heat the joint up red hot, then bend the "V" ends so they are parallel and look like the finished superheater tubes on the right (more heat on the outside). There are four of these in Big Boy and they extend all the way in the firebox, from one end to the other. We were able to fit them through the water tubes in the combustion chamber.

We have found that to be effective, superheaters must extend into the firebox. The block type of end obstructs the gas flow too much and if silver soldered onto the superheater tube, the joint won't stand up to firebox temperatures.

By the way, don't make any fittings out of brass, the dezincification process happens quite quickly (about 6 months of intermittent running).

Richard Trounce..