[ONDGAS]

So I rarely weld and I know these arnt the nicest welds but I was tiging some 316 stainless pipe using 309 filler and I have noticed that the welds are a little dark and "dusty" its even leaving a black soot when I rub my finger over the weld.

I did purge it by running 20l/pm for about 15sec and then let it sit at about 7l/pm while I'm welding.

Also I use a gas lens if that helps.

[cj737]

Others more metallurgically competent than I will chime in, but for the life of me, I can not understand why you chose 309? 308, or even better would be 316 filler. 309 is used with carbon->stainless weldments, not stainless->stainless.

Rule of thumb is the grade of stainless, or higher when welding. So you should be at 316 or higher.

[ONDGAS]

I have to admit that was my train of thought too but I was told ages ago that 309 is good at thermal flex and because this is a exhaust pipe it will resist cracking.... But I'm starting to regret it

[cj737]

An automotive exhaust from 316? You love yourself! I would definitely use 316 or better, with a purge (as you posted).

The other thing to realize, stainless material gets VERY GRAY and lumpy when overheated. You need extreme patience when welding thin wall stainless, even with a purge. Stainless does a poor job at thermal dissipation, so you can really drop your amps (from standard rule of 1:0.001) as you go. I might even suggest tinkering with pulse when welding stainless exhaust tubes. I find 50%, 25% and 1.2-1.4pps very workable for me.

If your fitup is really good, you can even fuse the weld as long as you have a solid purge.

[Oscar]

Without knowing all the details that only you know, we can only play the guessing game here: you used a tiny #4 cup, lingered too long taking your sweet time running the bead, which was way too long without stopping to let the part cool, and since you haven't welded stainless before, you didn't know this was even a thing to consider? Close?

[tweake]

a big thing with stainless is travel speed. you might drop the amps a little bit, but pick the pace up big time.

[ONDGAS]

Yeah I think everybody has done a good suspect profile on me on this one!

Im pretty sure it's a #6 cup

I pumped a fair bit of heat because when I initially started I noticed the welds were very narrow beads if I moved faster so I figured I would take my time and put some more heat into it and the bead widened so I thought I was doing the right thing. More is always better right? Works with ice cream....

Cj737. Plz elaborate on my choice of 316... Are you saying that's a bad choice? The reason is it's my own car and buying 3.5 inch bends bear me is stupid expensive, so I use a stainless supplier that does food grade stuff and other fab stuff that's not auto related. Also my muffler is stainless so I didn't want to use mild steel. Also I own a tig not a mig so stainless was a better option. Oh and also its my own car that will be lucky to see a 1000 miles a year

What really sucks is I have 316 filler on hand...

[tweake]

what angle did you grind the tungsten to?
to go wider weld make it a very sharp point.

i wouldn't use food grade stainless on an exhaust as the price is horrific.
there is high temp grades for making headers, but otherwise just use the cheapest you can find.

[ONDGAS]

Oh it isn't food grade pipe what I meant was its a general stainless supplier that doesn't cater to auto stuff so it's thicker than I would like it at 1.6 mm and the fact it's 316 was because that's just what they had.

So I'm confused, was using 316 a bad idea on my part? I thought the higher the number the higher the resistance to corrosion amongst other things

This is the tungsten in the pic

[LtBadd]

CJ can jump in, but I "think" a lot of exhaust are a 400 series stainless. 316 isn't a bad idea, you shouldn't have any corrosion problems, it's just expensive.

You'll probably have the cadillac of exhaust systems with 316

[cj737]

400 series is more common, but 304 is as high a grade as you need to go. Yeah, 316 is generally wicked expensive, but since you found a local supplier that had it, why not use it! I’ve done a few auto/moto exhausts from 321 and it’s very, very nice,

I use a gas lens, #12 cup, red tungsten (mostly a 3/32, sometimes a 1/16) and run 25cfh for the cup, 3-5cfh for the purge. I use 316 or better wire, even with 304 stainless (mostly because I have extra lying about).

You gotta slow down between welds! Let that tubing cool off! And lower your amps to say, 75% of wall thickness.

[ONDGAS]

Dammit so I did everything possible wrong.

I recently fixed up some aluminium issues because I wasn't hitting it with enough amps and taking too long to get the weld done so I just applied that thinking to this. It makes sense because this is the tail pipe section, I made the rest of the exhaust up about a year ago and my skills were worse then(if that's possible) and because I was doing welds in one inch incriments it turned out much better.

I will give it a go again and see how it turns out. Minus the 12 cup as I can't get one over the weekend

[Poland308]

Thin wall SS tube just requires practice. Yes it’s easy to run too hot and cook it. But you can also cook it by running too cool and heat soaking the part. From your pics I’d say your a bit on the hot side, your weld zone is cooked but the surrounding metal isn’t. You can try turning it down 3 to 5 amps at a time till you find the happy place. I’d recommend using the 316 or 308 as a second choice as others have stated.

[ONDGAS]

Ok so I had to weld the tip on, I got the fitment as good as I could and just used pulse and this is the result. You can see the factory welds on the muffler are a different colour. What determines this? Also, am I correct in that if I use a sharper tungsten I would get a wider bead?

Please give me some feedback on this weld.

[cj737]

Heat makes color in stainless. The hotter, the darker. A lite shiny “straw” color is about perfect. Yuor fusion weld looks much better!

You haven’t done anything “wrong”, you just made some choices that made things more difficult for you. It’s perfectly fine, really, so don’t regret what you’ve done.

When you did the portion, 1” at a time, that’s the way to work with thin stainless tubes. And a little tick for you, while the weld is hot and before it cools, brush it with your stainless tooth brush. It removes the color and leaves you with a nice silvery weld Your exhaust temps will color your tubing soon enough. Oh, and wipe the entire thing down with Acetone after you install it to remove any grease or oils or fingerprints. That will prevent them from staining permanently yuor beautiful new custom exhaust when you fire up and ride your bike.

You asked about tungsten angle: a sharper angle produces a slightly wider arc as the arc moves up the tip and away from the material before it “cones” off. You get less penetration as a result (not an issue here, but something to know) and a wider puddle. But, if you went to pulse mode, you can blast the material then trigger a low background amperage and you’ll get nice width, good fusion, and no cooking. It can also help you produce some nearly perfect welds.

A sample of some carbon square tube using pulse, no filler: (I attached this image to show the results can be better than you are ((or than I am is my point ))

[ONDGAS]

Thanks for the advice and great tip about the fingerprint tip that has caught me out before.

So your point about tuning up the pulse with a low background. Does that mean keep it moving really fast as to not get it too hot because won't that make it grey up again.

[cj737]

Not exactly. With pulse, you get a hot blast (peak time), then a cool blast of heat (background amperage), all metered by the number of pulses per second (pps). Personally I prefer a low PPS for tubing. It allows me to reposition on the BKGND pulse time to insure my tungsten and cup are correctly pointed to my work, and it gives me the time to travel a desired, perfect amount (well, as perfect as I am not).

I use 50% for peak because I can use a bit more amps to get a nice wet puddle, then I drop way down to 10% BKGND (this is 10% of your peak amperage) to get the puddle chilled, and not cooking) and I travel during the BKGND. The peak amp blast gives me a nice puddle, exact amount of width (add filler if using), BKGND, travel, PEAK, repeat...

What I find helpful with pulse on this type of job is the arc is bright durin peak, then dim (my notification to move) then bright, then dim. This is because of the low PPS setting I use (1.2-1.4). It’s like a metronome light. Makes getting your movements and positioning really easy. It will also aide you in finding the correct high amperage setting. I use full pedal when I pulse, because I’ve set the pulse configuration to my desired total, background and travel speed.

For instance:
Normally on 1/8” carbon I’d weld 120-130 amps, mostly full pedal with some tapering and mashing.
Now with pulse, I move to probably 150-165 amps because the duration of the total amps is much shorter.
For stainless 1/8”, I’d be at about 90 amps, maybe as high as 100. Heavy pedal work getting the heat down and up as I go.
Stainless pulse 1/8” I run 105, and no more than 50% peak, but all the way down to 10% BKGND (which is only 10 amps!) so I don’t overheat the pieces.

Does that make any better sense? Even with pulse on small stainless tubing, you still need to stop and re-position because unless you’re using an orbital positioner, you can’t reach. So do the same segments at the same time, then clock the tube and continue. It’s more efficient and you’ll get really nice results.

(This is the insiders trick to “fake it until you make it” so you’re exhaust looks like KaneKid or Mike Furick welded the darn thing for you!)

[ONDGAS]

Makes perfect sense thanks for that.

What do you guys think of using pulse to do a fusion weld, no fuller but no purge? I mean, it's a exhaust so it's not the most critical and if the weld isn't heated too much and there isn't the strongest penetration it shouldn't sugar inside considering its just a exhaust right?

I'm finding I really need to improve fit up and having no gaps its a painstaking job but it makes the welding heaps easier. Almost makes me want to redo the whole system again

[Poland308]

With out a purg a fusion weld will sugar. That will affect strength (it will make it brittle) and corrosion resistance. Defeating the whole purpose of using SS.

[ljdm1956]

Sad to say though, at the end of the day, my beautiful S/S headers and sidepipes get all colored up from engine heat anyway. Some color can be polished off, but worrying about weld colors when engine heat gives straw colors, etc...............constant struggle to try and keep them branny new looking.

[cj737]

With out a purg a fusion weld will sugar. That will affect strength (it will make it brittle) and corrosion resistance. Defeating the whole purpose of using SS.

Darn tooting! A really bad idea to fuse without a purge. You also are very prone to introduce undercut in the weld.

There’s a dichotomy of using stainless for exhausts: mild steel is far better at the thermal expansion/contraction and is more ductile, but more prone to corrosion. Stainless sucks at the thermals, but is very corrosion resistant. Most stainless systems fail because they are welded without a purge (even when a filler is used). Anytime I see a stainless exhaust and see that no purge was used, I won’t buy it. Yeah, maybe they will last 10-15 years, but they would last 50-100 years with a proper purge.

To LJDM’s point, yep, they do discolor from the heat anyway, but if you have oily smudges and fingerprints on the tubes when you first light up, those get baked in and are a real MFer to remove. Part of stainless’ beauty in my book is its colorizing with use (for exhausts). Just like Titantium. But coloring it for the sake of apppearances is not something I favor nor is it in the material’s best interest.

[ONDGAS]

Tell me what you guys think of this then, this guy is from a really reputable motorsports team and after seeing one of his fab guys welding up a section of exhaust with no purge his answer was
"on our application a standard weld hold sup fine, back purge would take more time without a pay-off, also in our experience if the part is fit well(no gaps) and the welder doesn't over penetrate, the back purged weld wouldn't be stronger. This statement is debatable though.
We never fusion weld, I don't believe that tig fusion welds are strong enough. We always use filler. "

Now admittedly their parts wouldn't be intended to last forever in the sense that a race car is only around for a couple seasons but he is saying a tight fit up + filler+controlled penetration=strong as, if not stronger than purged.

Thoughts?

[cj737]

He’s right, but also wrong. Any time you butt weld stainless (filler or no filler) there is atmosphere exposure which causes oxidation (sugaring) in the weld. Yes, heaps of Motorsport guys run exhausts without purging. They also discard these systems frequently. So they are not very focused on long term durability and they have a finance budget to pay for the waste, but no time to spend on making things “last”.

In their application, a filler welded joint without a purge will work just fine. It simply won’t last as long. As for taking more time though? Hogwash. It’s a very easy setup and in my experience, you can actually weld faster with a purge. Not that you can weld fast, but you can go faster than without a purge. If he’s talking about a slip fit joint, then there is less oxidation, but if you cut that section and examine it, there is most definitely oxidation behind the weld bead. Atmosphere is there whether they see it or not, and heat from welding causes disruptions in what you think is happening (at a micro level).

Are we splitting hairs? Yes. Butt/lap welds, always, always purge. Slip joints, it’s up to you. Purge is always better, no way around it.

[ONDGAS]

Got it, great info thanks guys

[Oscar]

If you're working with heat-sensitive tube-to-tube joints, this can be your best friend:



That is what I use, if needed. 1/2" wide, tinned copper braid. I use it to wrap both sides of the weld joint, at least 1/2" high, about 3/4" away from each other (~3/8" from each side of the weld joint).

Testing it out on titanium:




It serves two important and beneficial purposes:

• It creates an argon dam to help the argon linger around longer to protect the hot weld bead from oxidizing
• It quickly wicks out heat due to copper being the 2nd best thermal conductor, which in turn helps out the above bullet point about argon needing to protect the weld bead while it's still to hot to be allowed to encounter oxygen

If it works on titanium, which is notoriously worse for oxidizing than SS, it can work for pretty much anything.


Perfectly silver welds? Perhaps not, but it sure creates a huge buffer to counter unfavorable welding conditions. Thicker tubes/larger diameter tubes would probably benefit from wider braid and or higher number of wraps. The best thing is, as long as there is enough space to do so, you can't over do it---the more heat sinking ability you have, and the better the argon coverage, the better the welds can end up.