Welding Stainless Exhaust with Flux

[Richard86]

Hello, I’m about to embark on welding up a stainless steel exhaust system (304) for the first time and have a few concerns I would like your thoughts on.

I’ve opted to do down the Solar Flux route. I've bought this stuff. I’ve done this because I weld very slowly. I know this isn't ideal for SS, but will compensate with shorter stitches.
And it's not just the actual welding, but as I’m still quite new to this I spend a lot of time thinking rather than doing. It’s a hobby after all.

This means I would use a hell of a lot of gas back purging.

So my concerns are:

Butt Joints

Where I have a but joint, because I will have to apply the flux before tacking the pipe, will I not still have a gap where the weld is? Will it still work as intended? Or does the flux flow when heated to fill any gaps?

Lap Joints

When welding pipe to the silencer it’s effectively a lap joint with a perforated pipe sandwiched between the silencer skin and the pipe. I have no way of protecting this perforate pipe from oxidising. Is this just deemed acceptable?

Finally adding hangers.

This guy and video are excellent. They used solar flux and didn’t worry about any of the above so I’m probably over thinking it.

Towards the end of the video he adds the hangers to the silencers. There is no way of using solar flux inside the silencer. How is this ok?

Greatful for any thoughts.
Thanks

 

[Brad93]

Just purge your pipe if you’re that concerned or weld with no flux

 

[Munkul]

I've never even heard of stainless steel flux used like that... interested to see what it's like

It sounds a bit fiddly if you have to make it up with methanol each time though, almost as fiddly as just purging it.

 

[Shox Dr]

Even if you manage to get it to stop sugaring on the back, if you put too much heat in, the stainless will loose its properties.

sounds like you need a bit more practice.

 

[Aff]

I never even knew such a thing existed.

Hopefully you give it a go and show us (so I can save 30 quid giving it a go myself!)

 

[Richard86]

Just purge your pipe if you’re that concerned or weld with no flux

Why weld with no flux. I don't see the benefit of not using flux over using it?

It sounds a bit fiddly if you have to make it up with methanol each time though, almost as fiddly as just purging it.

This is true. I don't mind fiddly, what I mind is gas disappearing into the ether whilst I take my sweet time.

Even if you manage to get it to stop sugaring on the back, if you put too much heat in, the stainless will loose its properties.

sounds like you need a bit more practice.

My plan is to just keep the weld lengths short. Give it time to cool. Another reason to avoid purging with gas.
I generally find my ability improves much faster when welding something I care about.

​

I never even knew such a thing existed.

Hopefully you give it a go and show us (so I can save 30 quid giving it a go myself!)

This is the plan.
You should check this video out. It worked really well for him, but he was able to paint it directly to the other side leaving no gaps.

 

[Shox Dr]

Once you have a better understanding of the process, different materials and More torch hours, you’ll see alot of ‘helping hands’ ie flux is not necessary.

Its never a fast process either learning or finessing your talents after hours behind a torch.

I suggest you get hold of a load of suitable SS and practice, practice, practice

 

[gt6s]

Braizing flux with a drop of washing up liquid (wetting agent) then solvent, thinners white spirit etc.(Gritty paste) Does the same trick.

 

[a111r]

OP, I can supply you with methanol if you need any.

The SIF advert says it's non-flammable, yet it's used mixed with methanol.

 

[gt6s]

You let it dry. coats like a welding rod.

 

[Jedamere]

I've used a sif flux before on stainless as an alternative to purging and it was such a faff I just shoved tin foil in the end and a purge line to finish the job. The flux will work but any poor fit up will drag it into your weld, as will excessive penetration. Best of luck with it though, you might get better results than me

 

[whm_fab]

ive got Solar Flux type-B which is well proven over the years used for military purposes i believe. i very rarely use it, only in cases where i really need it and cant purge, cant remember the last time i did use it.

cant comment on the SIF product, didnt know anything other than Solarflux existed.

Its better than nothing, but it does suck in the flux into the weld and creates rock hard black glazing spots in the weld.doesnt make for a nice looking weld either on the front or backside.

Is it better than nothing and having sugaring on the back , yeah. would i ever substitute it for purging, especially on SS tube? Hell no

 

[Richard86]

I had a little play with the SIF Flux today.

I have to apologies for the welds, they don’t make for the best test. My excuses are:

1. I’m not very good at welding (yet)

2. This was a practice piece, so was playing with the amps a bit

3. I tried this cheapo no12 cup for part of it and no matter how much I cranked up the gas it gave me fireworks. It was sealed as far as I could tell, just seemed to cause turbulence or something. Sending it back. Back to the No.8 pink thing at 4lps and gas lens and everything was fine. Very strange.

4. You're going to have to take my word for this, the welds look a lot worse in the images than they do in real life. I blame the lighting. There, excuses over.

Just out of interest, I mixed up the flux yesterday (instructions say to mix with washing up liquid), but didn’t get round to using it as the kids needed my attention. Using it 24 hours after mixing didn’t seem to affect the results which is good to know.

Anyway, here is the pipe after welding. Don’t look too closely. You'll go blind.

And here are the comparisons. I did something slightly different on each quarter to see how it behaved. To be honest, I think as long as you get some flux on there it seems to work fine.

I like how the non-fluxed quarter bit still has a great big crack going through it. I’m sure that heat cycles and vibration from an exhaust will pull this apart in no time.

At no point did the flux pull through the weld.

I’m pretty pleased with this stuff so will continue to use it. For me it will work out a lot cheaper than back purging. In fact, this tub will probably last me 20 years (shelf life depending).

 

[Richard86]

OP, I can supply you with methanol if you need any.

The SIF advert says it's non-flammable, yet it's used mixed with methanol.

Thanks for the offer, but it's actually mixed with washing up liquid. I believe Solar Flux Type B is mixed with methanol. To be fair, you probably can mix it with Methanol, but washing up liquid seems to work well also.

 

[Turbo]

Have you ever tried purging? If you try it out, it's very unlikely you'll ever use that flux again, that's a complete faff!

If you set up your purge correctly you will use very little gas. For example to join 2 pipes.

Seal the open ends of the pipes with metal foil tape & punch a small hole for your purge pipe, push it in & try to seal around it. You only need a small pipe, we used 4mm nylon air pipe.

On the output of your argon fit a y piece & a second peashooter to feed the purge pipe.

Open up the purge peashooter high for a few seconds to purge the air from the pipes then reduce it down so that you can feel/hear gas coming through the pipe joint.

Tack up your joint.

It would probably be better to tack up the whole exhaust before welding it fully. If there are gaps in your joints tape up the tacked joint once its cooled to keep the gas in until you get all the tacking done.

Once the pipe is filled you are using very little gas to purge it. As well as giving a better internal finish it also helps cool the inside of the pipe so helping to avoid blow through.

But TBH you are maybe being to ambitious trying to TIG weld an exhaust. It takes a lot of practice & experience to become accomplished enough to produce good solid welds on thin wall tube.

Apart from high end stuff most s/s exhausts are mig welded. It's a lot easier, just as strong, not quite as pretty but it's an exhaust, under a car that will very quickly get covered in muck.

If you have a MIG welder you can get small 1kg rolls of s/s wire & you already have the gas.

 

[Munkul]

Looks good to me. Is it perfect? No. Will it hold together indefinitely? Probably

Thanks for taking time to show comparison pics. It's really interesting to see another method. It certainly looks effective in sealing the weld against sugaring

 

[Richard86]

Have you ever tried purging?

I haven't. I had a choice between buying the flux or the equipment to purge. Price was similar, except the purge also required additional gas. The flux has the advantage that I can take my time, let the piece cool, walk away, come back without using additional gas. For me, this makes the flux worth it.
The other benefit is for welding sheet SS where you can't easily back purge so the Flux is more versatile in the long run.
Weighing up all the above, if I had to pick one, for me, the flux is a no brainer.

But TBH you are maybe being to ambitious trying to TIG weld an exhaust.

This doesn't really align with my way of thinking. If it's tricky, more reason to do it.
I broke the pieces after taking the photos, bending them back and forth in a vice. The no flux bit held up really well. Took about 20 back and forth bends to split along the crack. My fluxed welds just broke in random places after maybe 25 bends (broke anywhere but the weld as the material is thicker here) so I have no concerns this will hold up with the flux (hell, even without the flux to my surprise, ignoring issues of corrosion).
It may still look ugly, but it will be better than the test piece, it will be strong, and at the end of it I will be a bit better at tig welding.

Thanks for taking time to show comparison pics. It's really interesting to see another method. It certainly looks effective in sealing the weld against sugaring

Thanks, I hope it helps someone. I agree, Flux seems to do a really good job. And it only takes a minute to mix up and you can then use the pot over a few days.

 

[Munkul]

Richard, there are exhausts holding together all over the world with snotty mig welds and rust. Your TIG welded exhaust will last longer than the lifespan of the car, even if you used no purge or flux at all As long as it's hung properly and has a flexible at the front.

 

[Richard86]

Definitely have flex pipes.
I'm quite looking forward to seeing how this turns out.

 

[yetta]

I am also a beginner to TIG and intend making a stainless exhaust. I did look into using the paste and found it expensive so bought a larger bottle of Argon instead, I hope to practice to make a reasonable job. How important is the flexy pipe? my engine is inline not transverse.