Soldering a Steel Tank - solder type and input needed

Hey everyone! I have a fuel tank that I modified to mount a flip-top cap. The steel mounting flange is riv-nutted in place, but I need to run solder around the outside of the flange just to seal it up. Could TIG it, but the rest of the tank is soldered, so it seems appropriate.

I remember soldering some steel up when I was a kid because I didn't know how to weld yet, but I only remember using a propane torch and something other than rosin core solder.

What should I use to do the job? Seam isn't really structural, so sort of low risk. This is just for sealing, really. Then the tank will get sealed with POR15 tank sealer after. OH! And the tank is new, so open flames are not an issue.

There will be a flange seal between the tank flange and the cap and each screw gets sealer.

Any help would be appreciated!

 

Best I remember, it was acid core solder, and be LIBERAL with the flux, and have it as clean as possible, so it will "wick" under that flange well!

 

That sounds right! Acid core solder...

Gonna' practice a bit on some scraps just to make sure. I assume a MAP Gas torch would be too hot, right?

 

Probably so, as propane used moderately , would probably work better.....................I have an old Craftsman electric iron, ( 1 1/2 dia., and a 3/4 wide tip!!!), that was my Dad's, and he repaired many a radiator with it!!!!

 

Does an electric iron like that take awhile to heat that metal up, though??

 

I would tin the flanges BEFORE putting the thing together. You will get full coverage and will be able to clean everything properly rather than poking solder and gobs of acid at a closed seam. I have used acid core and resin core, and on anything I could thoroughly clean down to bare metal the resin actually worked better. If you get the metal clean, flowing on solder will be easy, if it is corroded or dirty you will get poor coverage no matter what evil stuff you use!
Do you really want to seal this with solder?? Ifd you put a gasket made of something gas-proof there, won't that do the job at least as well??
And forget getting solder to wick into a closed area like that UNLESS you have already tinned the flanges. The only way I would do that would be to thoroughly tin both flanged peices, THEN bolt together, heat, and wick in solder. But why not a gasket on a bolted joint??

 

Yes tin the tank and then the ring so that you know that you have a good joint after the two get melted together.

 

I have found there is a lot of difference betweens brands of solder. Oatey is shit. Beads up like water on wax and will NOT adhere or wick. Forney is better, but not much. Will adhere but not wick. Kester is good, as is Bow. I can solder steel with those two using resin flux and the solder will wick into the joint. Just be sure the parts are CLEAN. Time spent sanding or coarse steel wooling is time well spent.

With Oatey and Forney, does not matter what kind of flux or surface prep. Piss poor results.

Bill

 

The new style plumbing solder (solid) that has no lead in it works well with the flux that's needed for it. And with the right prep (tinning) will do the job.

If you are using old flux, it might not work right, even with old lead solder.

Rosin is for electrical. Acid is for plumbing.

Flux core is OK for electrical. Not so much for plumbing.

What do the body guys use for flux on a lead job?

 

Bruce and Tommy,

The flange isn't bolted to the tank and cannot be removed. It's riveted with Rivet-Nuts. The Rivet nuts essentially are a hollow rivet with a thread inside. They do double-duty by acting as the structure components that keep the flange to the tank AND act as nuts for the 10-32 screws that are used for the cap itself. There will only be a gasket between the cap and the flange because the cap will be removable. The flange will not be removable.

I cleaned up the flange on the bottom side REAL well. 120 grit, bare metal directly to the cleaned up face of the tank, also hit with 120. Bare metal to bare metal, but I did not tin it first. Didn't think of soldering it until after the fact. Was going to TIG it, but then decided it just wouldn't look right compared to the rest of the tank joints.

Once I seal the tank, it will get in all the nooks and crannies from the inside, but I want to finish that flange edge off by joining it to the tank, itself. PLUS! Than tank will be painted, so it HAS to get finished. I don't want the paint to lift in that area.

Here's how it looks with the cap mounted withOUT the gasket for the cap in place...

 

I do a fair amount of soldering as well as some lead work and I use both acid and Rosen core on some projects but I also use silver solder which is stronger but requires you add the flux or tining solution. I use the same flux used for doing lead work. "Tins-Tyter" by Balkamp is a good tining fluid (liquid flux). Of course you can also use body lead which is usualy 60/40.
As already mentioned...Make certain you tin both surfaces after thoroughly cleaning them. Once they are both coated you can assemble the pieces and then heat the area so that the lead melts from the heat of the metal rather than the heat of the torch. Be careful to use only enough heat to allow the lead ( or solder) flow into the metal..... Too much heat can be as bad as not enough especially if you are using self applied flux....

Be sure to thoroughly clean all the flux off after your finished soldering as it can set the stage for corrosion

Personally, I'd just use a gasket.... Lots simpler.

 

I would go with Bruce's suggestions on the pre tinning. Try to locate a product called a tinning flux, this has solder within the flux. A solder with a small percentage of silver is going to be stronger and less likely to shrink or crack. I think I would try to use a solid core solder and use either a wax based acid or a talo to inhibit the oxygen. Generally the core type solders are going to be prone to inclusions and voids in the solder joint. I think a MAPP torch will work fine as long as you work your heat properly.
I like the idea of this because the dang gaskets on mine just got alcohol rotted.
Good luck.
There's a solder manufacturer in Chi town here Ames Metal Products, google em up. They may have some of this, it's getting rare. Good luck.

 

Flange is already riveted in place. I can't use a gasket between the flange and the tank. Has to be either welded or soldered. I would prefer to solder because the rest of the tank is soldered. TIG welds are going to look totally out of place with the rest of the tank.

Gasket will ONLY be going between the cap and the flange because the cap is removable. Thank flange is NOT removable.

The soldered joint will only be there to create a seal. Nothing else. The rivet-nuts are what keep it in place as well as the cap. And had I thought about it, I would have tinned the faces first... But I didn't. So here I am.

 

Well then it will take a pretty big iron like the roofers use for the copper standing seam roofs. The gap between the two pieces will act as an insulator for any small electric iron. Having the right tool for the job is always the key.

 

Well. You can either drill the rivets out now and tin the stuff up to get a real good quality seal or play "Vegas" and roll the dice on a schitt job. You seem like the sort of guy who is going to drill out the rivets as the percentage of quality and victory is greater that way.
Even if the rivets are original old school parts, I would still pre tin this. Sorry.

 

Why not just use a epoxy adhesive applied from the inside of the opening and using a heat gun to make it wick in nicely between the two parts. Else drill out the rivets and do it right if you absolutely need to use solder.

 

I'm 99.44/100 sure you will be fine with letting the solder wick into the joint. As long as rust didn't start in there yet.

Try it, if it don't wick nice, you can then drill out the rivnuts and tin the pieces.

 

Didn't want to drill them out because every time I drill them out the holes gets bigger and the grip of the riv-nut decreases which increases the possibility of spinning a riv-nut when tightening the screws.

I could try to raise the edge and get some butter under there to help it flow and then tap it back down. Seems like the best option. Not trying to do a "schitt" job. I'm in a pickle with this thing and I'm trying to reason out the best option. If I F-up the tank I'll be waiting another 4 or 5 months to get one. I'm trying to be wise about what I do here.

If it doesn't work I'll just have to dig out the solder and epoxy it. TIG welding probably won't even be an option after trying to solder it and I can't keep sanding on this tank around the filler cap flange or I'm going to run out of metal. It appears to only be 20 gage.

Thanks for your input folks! It's appreciated!

 

Scooter, the job of the flux is to help pull the solder in there. You don't tin a cooper pipe solder job.

Even furnace brazing uses the flux to pull the brass in.

 

Tin or leak, your choice. I solder A LOT, due to my job. Silver solder would be fine, but REALLY spendy and you don't need that kind of bond. I always tin a joint like that.

 

No you don't tin a pipe solder job but the joint is designed to pull the solder in to it and you also flux the joint real thoroughly. There are a few types of liquid fluxes on the market, I don't like them in general because they are not as easy to apply. I suppose that if you saturate the joint with liquid flux that you will get a decent flow and seal there.Your temp range is right around 450 to 465 on these solders. I know you want this to look nice, I've followed your build, All I can recommend is a bunch of practicing and I think even follow through to some neutralizing of the fluxes so they don't cause a paint problem.
If all fails you would just warm the area and scotch brite off the solder that burned, warm it and wipe it off with a rag and reapply the flux and go again. And if you TIG it just warm it, wipe it to very clean and scotch brite it out,It really only surface bonds and does not dig in all that deep.
A silver based plumbers solder would not be that pricey. Then again just a regular roll is about 35 right now.
You know I had a thing I needed done and a silver smith guy had a lot of tricks on it, they may have some good sources for stuff.

 

Scoot - Drill the rivnuts out - you know you aren't going to be happy if you don't, you anal-engineering type, you. Drill just undersize and then punch them through, just like properly removing a rivet. No oversized hole then. If these are the good ol' BFG or other steel rivnuts, what I like to do is after I set them, I turn the heat on the tig WAY down and with a 1/16" tungsten make 2 small tacks (180* apart) which gives me peace of mind that they won't turn spinner on me if I stupidly over torque their bolts. For soldering advice, I'd listen to the plumber, who has probably done more of it than most folks. vic

 

I definitely know what the flux is for. Fully planning on fluxing like crazy. Wire a ton with rosin core for wiring jobs, but never done much for plumbing or structural.

I'll check around for the liquid flux and if I have to drill these riv-nuts out then I have to drill them out. Is the liquid stuff something I can just get from the hardware store, or is this a special order type of thing? Is it thick enough that I could put it in a bottle cap and brush it on with an acid brush or something?

I certainly don't disagree with you or anyone else that's offering advice. If I didn't want it, I wouldn't have asked for it, and if I already knew how to do it right I wouldn't have asked then, either. But, I'm far from being experienced in this type of thing so I figured I better start learning and asking questions.

Thanks for the input!

I hope I don't have to, but if I do, I do...

 

I'd use 50/50 solid wire solder (not acid core) and Nokorode paste flux. 50/50 is much easier to maintain at just the point of melting than any of the typical lead free plumbing solders on the market today.

Another good option would be Harris Sta-brite #8 which is a 8% silver bearing soft solder. Sta-brite is used with a special flux also made by Harris. Flux is mild and the solder itself makes a good strong joint and is easy to work with. Downside though it ain't cheap. Haven't priced any recently, but with the current price of silver its probably $60 or so for a 1# roll.

Nokorode is one of the mildest fluxes on the market. Available at most any plumbing supply house. The solder is not going to wick full depth under the flange, but the flux will. The problem with using some of the strong fluxes is that they sorta keep on eating on stuff forever. They will cause corrosion between the flange and the tank over time in any area the solder doesn't wick into. Nokorode won't cause that problem.

I'd keep the heat low and somewhat back on the flange rather than right on the joint. Looks in the pic like the flange is heavier gauge material than the tank itself, so you should be able to get adequate heat transfer thru the flange and into the tank. If you heat right along the joint itself, chances are you'll end up with a bead that's sorta like a cold joint made with a mig gun. Looks okay but doesn't hold up long. Most important thing is to keep the overall heat to a minimum and let the metal itself, and not the flame, melt the solder. Keeping the heat back on the flange will tend to draw the solder into the joint better.

I've made a lot of similar joints, mostly in repairing stuff, and its not a big deal as long as you start with parts that are meticulously clean via sanding the surfaces. Don't even think about any kind of solvent because they'll all leave a residue that'll keep the solder from bonding to the steel. And keep the heat as low as possible.

This joint is a perfect application for Everdur silicon bronze brazing rod and tig. Using the Everdur as a filler, and heating with the tig torch, you can run a row of dimes around that joint without melting any steel. There's a pretty good article on this technique at http://metalshapers.org/101/covell/covell-silbronze.shtml A sheetmetal man at my dad's shop taught me how to do this when I was 14 or 15, and with a half hour of practice my joints looked like I knew what I was doing. At that time I had zero tig experience, so for anyone with experience its an easy skill to pick up.

 

The 50/50 has a larger working range of about 40 degrees over the other solders, but my fear would be that the tin lead would fracture on him and not have a good tensile strength. I only like the silver here for strength and bonding ability to the steel surfaces.
If you practice a bit soldering a thicker steel part to a thin sheet you will have a lot of what is being said occur right there in front of you. The steel will always seem to hold just a touch of some contaminant usually oil, that causes the surface to oxidize and sour to the solder. The bond from steel to solder can be a bit tricky and even an old dawg at it like myself has to flux the steel a tad to sweeten it towards the solder with a bit of flux during the process.
A lot of these products can be found at plumbing and or heating supply houses or Grainger or McMaster.. You can use a small brush to wick or feed a bit of extra liquid flux into a gap, if you get brushes buy a few extra, they burn up fairly easy.
You have a lot of good info, mess with it a bit and do a few trials.
I'm just putting a bit of extra info in here for you because I know you are a perfectionist, I'm sure it will turn out great. Have fun. Let us know how it goes.

 

Wow! You guys are incredible! That's some crazy information! My head is spinning right now...

I woke up this morning and one of the first things I thought was, "drill out the riv-nuts". Dammit... Gonna' blame it on Vic if it gets screwed up.

So I'm going to drill out the rivet-nuts and flux the surfaces before re-rivnutting.

So thinking in-terms of assembling it with flux between the surfaces, should I figure coating it about 1/4" in from the edge of the flange should wick the solder in far enough? Should I use the "Nokorode" flux to help prevent corrosion between the flanges, since I won't be able to get in their and neutralize it later?

So should I avoid the Acid Core, even though it's not really a structural seam? $60 for a roll of solder I will probably only use once in the next 10 years sorta seems like a waste.

Was thinking back to the 50/50 mentioned... THAT'S what I used when I was a kid, soldering up little model car frames! I remember now! I was like 9! HAHA! I remember my Dad telling me that the rosin core wasn't the best for the job and to try "this stuff", and handed me a white plastic spool and I remember the red lettering and "50/50" being on the spool... Geesh. I'm full of useless information. I don't remember ever using flux, though. HAHA! D'OH!

I order from McMaster Carr quite a bit, so if I can get this straightened out, I'll just order what I need if I can't get it at my local ACE around the corner.

 

The main advantage to using Nokorode flux in an application like this is that it doesn't have to be neutralized. You can smear it on a piece of bare steel and wipe it off a year later and the surface will look about the same as if you'd smeared grease on it.

Nokorode is not a self cleaning flux. Any of the ones labeled as self cleaning are far more agressive and do require neutralization to stop them from corroding the metal over time. Because its not self cleaning, the cleanliness of the surfaces is more critical. Sand with about 120 grit paper and make sure you don't touch the surfaces with your fingers. The oil from human skin is about as effective in keeping the surface from tinning as pouring a quart of 30 wt on it would be.

The acid in acid core solder is just one more of those things that can cause corrosion over the long term, hence the recommendation of solid wire solder.

Be cautious of any flux coming from a hardware store. Most of those are made for amateurs who don't understand the term "clean", so they're self cleaning and aggressive to aid Joe Homeowner in getting a leak free joint on his water line that he "cleaned" by wiping with a dirty rag. Hardware stores may not keep anything but lead free solders these days since most of their sales would be directed toward people repairing or installing potable water lines. Any plumbing and piping supply house should have 50/50 though, since its still legal for use on lines used for heating and cooling purposes.

 

Okay! Great! Thank you!

Think I may shoot for a 50/50 and some Nokorode... The metal is new metal and cleans up easily, so should be good there.

 

Geesh... Can I even get 50/50 in California?? Just thought of that.

 

Lots of good info here on the soldering, but it seems you are going to have to drill out the nut-serts unfortunately. I know watching your build, you are way too much of a perfectionist, but I would probably just TIG it at this point.

Mainly, I just wanted to say how bad-ass your choice of fuel caps looks! Your car is looking awesome!