Genuine honest feedback on stainless TIG welding

[Bowie69]

So.... after the fun I have had with aluminium TIG, a friend asked me to have a look at their stainless exhaust system which was cracked in one place and had been bodged in another.

I've mostly been practicing and just tacking things together, and progress is being made. It is made doubly fun as being pipe it needs (depending on who you ask!) purging, but have got that set up now with a Y-splitter and a separate flow meter.

The problem, if indeed it is, is that I am still getting some oxidisation on the welds -they are appearing rather grey.

The material is 1.2mm wall 304 stainless pipe, welding with a 1.6mm 308L filler rod (when not autogenous), pure argon, running ~10l/m, tungsten sharpened to a nice point and kept clean, base material sanded clean and wiped with acetone inside and out, filler rod wiped with acetone.

I have tried a lot of different things:

• Swapped to a gas lens and a no 10 cup (some improvement, especially in the HAZ)
• Different tungsten (one more to try tomorrow)
• Different current, from 30 (waaaay too cold) up to 70A, which was a good way to make a mess, it 'feels' like 40-45 is more where I need to be.
• Increased/decreased gas flow from ~5 to 20 l/min
• Speeding up (when there is more current) and slowing down

The biggest improvement on the top side of the weld was the slightly larger cup and gas lens, I have a 12 coming tomorrow to see if that helps more, but I am not that convinced.

I guess there are a couple of questions I could really do with an answer to:

• Yes I know the internet is filled with lovely colourful welds, but is a slightly grey weld actually OK as long as the oxide is not included in the weld puddle?
• What else could I try (if first question indicates a problem)?

So at the risk of complete humiliation  here's a couple of pics of efforts so far... Note I've just been experimenting rather than trying to perfect the technique  

This one is quite useful, when I was experimenting with current, that's most, medium, least from left to right:

 

A (very) quick rub with scotchbrite makes them look more like this:

 

Thanks for any help

 

 

 

 

[landroversforever]

To me, grey means it’s a bit hot, so either not enough travel speed or too many amps. Depending on the application it can be ok.

Not relevant to these tests, but always worth remembering weld order on a back purged tube. I’d always start with the joint closest to the purge point so you’re not drawing in air from the joints. 

[landroversforever]

Are you inside/outside? 

or in one case for me…. Inside but with a fan going  

[Bowie69]

Inside, no fan, closed garage door, made no difference.

Like I say the weld on the right is ~30A, weld on left ~50A or so, but am travelling pretty fast when running up there, 30A hardly forms a pool.

This was purged at the time, as wanted to see the effect on the inside, which actually was quite acceptable looking so I am assuming the grey os not contamination from the back side of the weld. 

There were no other gaps in the tube, and as you can see these are just run straight on the pipe, no joint to make, early on I did realise I needed to move the purge pipe to the other end

 

[landroversforever]

One thought - its not something silly like a coating on the tube? Have you tried putting down a weld on a section you've ground back and then cleaned? 

[landroversforever]

Also for the 3 power levels, having done a weld nearby fairly shortly before can have a big effect on the amps required on the next one. Probably less of an issue here as all three show a bit of grainy-ness. 

[elbekko]

As far as I understand, back-purging is mainly for stopping sugaring on the back side of the weld, not so much structurally affecting the weld.

A few thoughts:

* you've not accidentally grabbed the wrong bottle of gas?

* is the back-purging too high flow so it's blowing into your weld puddle?

No TIG experience (yet), but at first glance I'd say those welds are definitely contaminated. To be sure, cut one in half lengthwise and see how the full weld looks.

[Bowie69]

2 minutes ago, landroversforever said:

One thought - its not something silly like a coating on the tube? Have you tried putting down a weld on a section you've ground back and then cleaned? 

Hmm, perhaps, I did red scotchbrite it, but maybe I need to be a bit more aggressive -there are other welds that look similar on fully satin looking stainless that had more of a going over.

Will give it a try tomorrow:)

[Bowie69]

Just now, elbekko said:

As far as I understand, back-purging is mainly for stopping sugaring on the back side of the weld, not so much structurally affecting the weld.

Mostly, yes, but there was really significant sugaring on the inside which would affect longevity, especially with all the corrosive stuff coming out the exhaust continually bathing it.

 

1 minute ago, elbekko said:

you've not accidentally grabbed the wrong bottle of gas?

Same bottle I have been using for aluminium, and no contamination over there.

 

2 minutes ago, elbekko said:

is the back-purging too high flow so it's blowing into your weld puddle?

Suspect not, to initially purge I was at 10l/min, dropped to 5l/min once I started welding, which was effective (see comment to Ross)

 

2 minutes ago, elbekko said:

cut one in half lengthwise and see how the full weld looks.

Good idea, will do so tomorrow.

Thank you!  

[Stellaghost]

A guy I work with  is a welder by trade and very good at tig

I was asking him about stainless tig as I also get grey welds, his reply was the gas is the issue. He also had the same issues, trying different cups, gas lenses, etc until he found out the lovely coloured welds on YouTube are done with a gas called Heliox

HTH regards Stephen 

[Bowie69]

Thanks Stephen, yes, heliox or something is argon helium mix as I understand, but somehow this evening I managed this:

 

Which is looking much more satisfactory. 45A, 10l/min.

As you can see, ground back the base metal, now with 12 cup, I did also swap out the tungsten.... 

Now going to pull out one at a time to see which fixed it(!) 

[Bowie69]

Un-ground base material (ignore the spot):

[Bowie69]

Swapped tungsten back out, no difference, swapped to 10 cup and it all went grey again! Number 12 went back on... That looks like:

I did play with heat, went up to 50A and started to get so grey coming back, so clearly I can't move fast enough yet 😛 55A was even worse. 

Settled around 42A for this material, gives me enough time to make sure the puddle can be managed. 

I did feel a breeze or two of wind in the garage, which I could see immediately blue the weld, amazing how sensitive it is.... Will need to shut the door next time. 

 

 

 

 

[hurbie]

i have never seen the steel gauze in a tig cup ..... to me it seems the gas is not capable to shield the weld before it cools enough , so causing it to oxidize (i have never tig weld with such a big gas-cup , so maybee the smaller cups are from "yesterday" (i'm getting old ....))

[Bowie69]

Yep, certainly appears that way to me, the 8 or 10 just wasn't quite enough to keep things shielded properly as it cooled down - this is all new to me, to date I've only tigged ali, which is not a reactive metal, so gas coverage is really not important, I used a 6 cup normally and it works perfectly. 

The gauze, as well as the gas lens is designed to give more even coverage on the weld, it seems to work. When the gas switches off after ~8 seconds the covered bit of weld goes from shiny stainless to blue within a second. 

I've seen some comments about torch angle being a possible cause of grey welds too, so will be keeping an eye on that if it happens again. 

[landroversforever]

5 hours ago, Stellaghost said:

A guy I work with  is a welder by trade and very good at tig

I was asking him about stainless tig as I also get grey welds, his reply was the gas is the issue. He also had the same issues, trying different cups, gas lenses, etc until he found out the lovely coloured welds on YouTube are done with a gas called Heliox

HTH regards Stephen 

Plenty of stuff done at work (nuclear engineering stuff) with colourful welds done with just argon. I just needs the right settings and process. I’d say the gas coverage being the most important as I noticed a huge jump in the ease of getting colours when I swapped to a gas lense. 

[landroversforever]

Collet vs gas lense type looks something like this in the was the gas coverage:

[Hybrid_From_Hell]

OK

My 2ps worth

 

Anything that's grey is either / or / both too hot (too many amps) / Contamination

 

Now, guessing this is a "Not New" exhaust ?

if so you need to flap pad the area as it will have contamination on the surface, acetone etc won't be anywhere near enough. 

clean a good 1" either side nice gentle flap pad too ....

Don't use a grinding disk, other than being too rough it will leave bits in the stainless

When I do stainless I use Pure Argon and a BIG cup 12 / 14 gas lends and gas flow up to 20-25 and use a bigger rod if need be, make sure tip ground right direction esp stainless !!

 

1.2mm is bloody thin, so I would say a few amps either way will make more difference than you might think, also so does TIG tip shape

Obviously it should be a nice sharp point, but a "Long" point will make the weld much wider, and vs a "Short" point bring the weld line in tighter

A Long point will behave like MORE amps big wide weld, and a short feels like you have less amps, if the gaps you are welding are tight go with a medium or better short point and try different thicknesses of rods.

 

I would start at say 35 amps, short point 20-25 plus large cup, and have high say 7 seconds pre flow and same post flow and hold the rod and the weld under the cup until flow starts and absolutely when stops.

then go say 32 and then 37 and see what is better then do the same again +1 -1 on whichever best and so on until the amps are seemingly best.....on 1.2mm a few amps makes huge changes

Lastly - might not be pretty but use say a 2.4mm vs a  1.6mm rod and that gives you more metal flowing than a smaller rod, ...try it

 

I use purple Blue / Gold  Tunsgtens and on something like 1.2mm I'd be on a 1mm tungsten or 1.6mm Max.....

and forget purging - nice but its an exhaust not an aircraft

 

Hope the above helps, and yes I TIG regularly...... not a google / armchair expert....try the above and let us know !

I have all sort of rods thicknesses etc etc, if you want some samples I can post you some, just ask 

 

Nige

 

[steve200TDi]

Good info Nige!

I've been welding recently with a long point and it's true what you say I've found I need more amps and it produces a wider weld.

I will definitely been trying it again with a shorter point.

Steve