What's going wrong?

[James1433]

Im setting up my new R Tech welder and had a practice with mild steel and stainless steel. I keep getting what looks like porosity in my welds and the stainless welds always look burned. This bit of stainless tube is about 1.5mm wall and i as on 60 amps, 1.6 tungsten, no5 cup and 7 lpm gas flow. I have a stainless exhaust to make soon so would like to get my welding up to scratch before i start. Also considering getting a spare bottle of argon so i can purge the inside of the tube.

 

[langy]

60 amps is too high for 1.5 s/s, You would be better to master mild steel before moving into stainless, you can also knock the gas down a bit too, I use 4.5 on s/s

 

[Richard.]

Along with what's said above a no 5 cup is very small. I would use a 7 or 8 with a gas lens for stainless. I don't think the flow rate is too bad really. Your too hot though I'd suggest 35-40 amps. You should definitely be purging inside.

 

[cianh91]

Try cleaning the mild steel first the scale on it could be causing your porosity

 

[Richard.]

Try cleaning the mild steel first the scale on it could be causing your porosity

Stainless, and it looks pretty clean to me. Although I forgot to ask what filler are you using.

 

[langy]

Along with what's said above a no 5 cup is very small. I would use a 7 or 8 with a gas lens for stainless. I don't think the flow rate is too bad really. Your too hot though I'd suggest 35-40 amps. You should definitely be purging inside.

I agree with Richard about the gas lens and 7 cup but you don't need to purge, I only purge my systems if the customer ask for it, Its not a necessity.

 

[AndyS2]

As everybody else has said, too much heat caused by too many amps. I use 35amps for welding 1.6mm stainless on exhausts, get the fit up nice and tight and you won't need an filler.

 

[hotrodder]

Read this thread http://www.mig-welding.co.uk/forum/threads/tig-welding-stainless-manifold-help.23592/ and check out http://www.mig-welding.co.uk/tig-tutorial.htm too.

Looks to me like a combination of too hot/too slow with too long of an arc length which is compounded without a purge- back of the joint is oxidising and the oxides end up in the weldpool. Improving the shielding at the torch won't achieve much if the backside is being cooked.
While it's possible to weld thin stainless without a purge (for many but not all apllications) and not make a mess you need to be a pretty good hand to not cook all of the chromium out and produce a manky grey mess that's no longer stainless... a bit too hot or slow and it goes wrong very quickly

ETA you don't need a second cylinder for when purging is necessary, just a http://www.weldequip.com/twin-outlet-valve.htm at the regulator outlet and (ideally) a second flow meter for the purge

 

[norlander]

You should normally back off the amps a bit for SS compared to mild steel, for back purging, you can buy a decent disposable bottle regulator from weldequip, and hook up a dispo bottle to back purge if you want.
I find I can get away without backpurging most of the time because I have a pedal now and you can back off the amps,and you have a feel for the depth of penetration. In other words, foot controlled pulse-many pedal users say they don't use pulse-but they do-might be widely spaced pulse-but they are pulsing.
I like to use a large cup and up the flow a tad for SS. My beads look a bit stringy and mean, but the zorsts hold up ok, I like to get the Ti rainbow colours if I can, I just feel I am not going too hot and not penetrating into the inside of the pipe that way, seems to be born out in practice so far.I bung the post flow up too.
Be aware that there is expensive kit for cleaning up SS welds http://rapidwelding.com/dynamic/DisplayItem.aspx?c=924-RS&zl=1 so colours are recognised as being somewhat inherent to the process.
If you don't have a pedal, try the pulse on your machine, bit odd at first, but puddle, push puddle and dab filler sort of thing, not same control as with a pedal, but see how you get on with it
One point, arc length, if its too long in TIG you can fire a lot of heat into the job, when you first start, there is all hell going on with TIG, you stub the filler in to the tungsten, or ball the filler up, etc.
With tube, do about 25mm, reset the job on the table and do the next section.
I clean my stainless up more prior to welding than it looks like you did in the image?
My exhausts get wrapped, so the actual appearance of the welds is not an issue.
Any colours in SS after welding can sometimes be eliminated by brushing with an SS wire brush immediatley after welding, but it won't normally work if you leave it too late

 

[Richard.]

I agree with Richard about the gas lens and 7 cup but you don't need to purge, I only purge my systems if the customer ask for it, Its not a necessity.

I know back purge is not always needed but I would say in this case It would help. Unless his current/travel speed are excellent the weld becomes too hot and Virtually unalloyed. having the gas on the inside will help this along with back side protection from oxides.

 

[James1433]

Thanks for all the feedback. I went and had another go at 30 Amps and it looked alot better. Purging using a disposable bottle or T off of my main bottle sounds like a good idea and a cheaper option. This bit of tube is only a small offcut but will practice with purging before i have a go at welding up my exhaust. Will have another go tomorrow and take some more pics.

 

[Richard.]

My last 2 manky bits of 1.5mm 304. 35 amps, 1.6 tungsten, 1mm 308 filler, no7 cup , 6llpm, didn't back purge this and it doesn't look great to be fair and post gas should of been adjusted to longer but it's a guideline on settings.

 

[Leetig]

Hi James. All advise above spot on as usual. Today I started practicing on dairy pipe in school. 2 inch 1.6mm stainless. Tricky stuff to get the hang of!! First few ended up with holes in and similar looking bead as yours. Thing I found worked for me was using slightly more amps and travel quicker i was using 40 amps. As for mild steel shinny metal and tight arc.

 

[Paul G]

This is yet another thread that I can't get my head round. What is this thing about not using argon?

On an average butt weld in thin wall stainless I'll run 12 or so lpm. That's 7 to 8 though a decent sized ceramic.
( The one on the left is a small one, about the size of my first finger.) The rest is used to purge.


What's the point of using expensive materials like stainless, and then try to save tuppence ha'penny on gas?

That's like having a £2.5k dual fuel Aga range cooker fitted in your kitchen, then living on Tesco "Value" baked beans.



Paul G

 

[norlander]

Yep, I do like to bung me gas up, and I have difficulty getting the larger cups from my shop cos they think I'm a mad Rosbif. The reason I mentioned the dispo bottle set up for purging btw, is because again, over here, they think I'm nuts when I ask for a reg set with a take off for purging, so I got the dispo reg from weldequip (any other types are useless) and just use dispo bottles to BP.

 

[Richard.]

This is yet another thread that I can't get my head round. What is this thing about not using argon?

On an average butt weld in thin wall stainless I'll run 12 or so lpm. That's 7 to 8 though a decent sized ceramic.
( The one on the left is a small one, about the size of my first finger.) The rest is used to purge.


What's the point of using expensive materials like stainless, and then try to save tuppence ha'penny on gas?

That's like having a £2.5k dual fuel Aga range cooker fitted in your kitchen, then living on Tesco "Value" baked beans.



Paul G

I agree Paul I pretty much back purge all thin walled/full pen stainless butt welds. The example I shown above I didn't bother as was just to give an idea of settings but if it was on a job there would be a feed of argon on the underside and the surface finish on both sides would be improved further.

 

[norlander]

This any help? BTW- my workshop and bench are just like that, I have oxides on my backside as well, but there is a good ointment for that.

 

[whm_fab]

This is yet another thread that I can't get my head round. What is this thing about not using argon?

On an average butt weld in thin wall stainless I'll run 12 or so lpm. That's 7 to 8 though a decent sized ceramic.
( The one on the left is a small one, about the size of my first finger.) The rest is used to purge.


What's the point of using expensive materials like stainless, and then try to save tuppence ha'penny on gas?

That's like having a £2.5k dual fuel Aga range cooker fitted in your kitchen, then living on Tesco "Value" baked beans.



Paul G

i agree, there is alot of bad/incorrect advice in this thread.

For folks that said because they back off the amps and use a pedal you dont need to backpurge is frankly BS. You CANNOT get a full penetration stainless tube weld with no sugaring without backpurge/solarflux - not possible. if you do, you havent got full penetration and an xray quality weld. Same goes for skimping on gas as Paul has said. 4lpm or S/S is just asking for trouble, either do the job correctly with the correct equipment or dont imo.

I agree with Richard about the gas lens and 7 cup but you don't need to purge, I only purge my systems if the customer ask for it, Its not a necessity.

Im sorry if this seems harsh, but that is terrible terrible advice.
If a customer asked me to make a manifold without purging id laugh and tell him to take his business elsewhere. You must purge stainless for full penetration welds. your exhausts will corrode from the inside and become more brittle than they already are.

 

[James1433]

Thanks again guy's. Like i say i will be purging when i come to do the job for real. Will have another play with settings tonight. Might play without filler rod to and pulse settings see what i get. Would like to polish the welds smooth after though so may need to build them up 1st.

 

[norlander]

Its bad advice relative to your level of work and your workshop equipment. Down in the shed, in less than perfect conditions, we do what we can with what we got, and, not all of us require EN/ ISO 3million part A- X ray, etc, because the job is for us-so we weld as we can, yank it about a bit in the vice, and if it dunner bust, jobs a gud un.
I don't want max penetration on every bit I knock up-it causes me problems with fit up.