Thread: Must be doing something wrong

(But I don't know what)
I was running a TIG weld down 2 pieces of MS today and was getting porosity. It happens every so often and I don't know what the cause is. I did a web search and a few possibilities were suggested but I think I've covered them. Any ideas from the floor?

P1010942 (Medium).JPGP1010943 (Medium).JPG

The weld was to cover a joint in some thick plate, so more cosmetic this time but I was hoping for a nice neat weld. I also get this on thinner material as well. As you can see from the photos above, there is the occasional void that breaks the surface but most are beneath. Grinding back shows the voids in the weld bead and if ground back flush there is a row of pores (below)
P1010949 (Medium).JPG

The weld was on some black steel that I'd milled the mill scale off yesterday. Prior to welding I wiped it down with acetone, so I don't think clean is the problem. Argon flow was between the recommended limits (8 to 10lpm) and I purge the gas line before I weld. Current was set at around 90A max (varied with thumb control). I tried altering the cup angle, speed and a few other things but didn't get any different results.

Any other thoughts on what could be a cause?

Michael

nasty.
What's happening while you're actually welding? is it fizzing? sparking? etc.
If the metal is ground clean back and front and the metal is in fact mild steel and the filler is compatible then I'd be suspecting the old leak in the argon hose culprit.
Maybe give a list of what you're already ruled out?
Cheers
- Mick

I can't say what I've ruled out as not having a clue I'm not sure what to rule out.
Metal was certainly clean. Clean gloves too, so no oily prints back on the metal while positioning it.
Not sparking or fizzing. If it wasn't for the occasional void breaking the bead surface I would have thought them acceptable welds.
Welding rods are Comweld LW-1 copper coated filler rods (ER70-S I think - box is in the shed). I keep them in a tube so they are not dirty or damp.
I did have a cracked hose some years ago on a sharp bend but since fixing that, they look to be fine (by the way, the whole rig is around 8 years old). The only hose that regularly gets tugged and moved around is the little one between the machine and the torch lead and I am careful not to strain it (doesn't mean that it may not be cracked I guess). I have also made up a little cap to fit over the torch cup when it is not being used to try and keep any moist air out. I'm wondering whether the gas flow is too slow. I was using a 6 cup and a 2.4mm electrode. My cheat sheet suggests that a 5 might be more appropriate, but at the same time I wouldn't have thought it critical. Electrode stick out around 6 to 8mm.

Part of the mystery is that I only seem to have this problem with steel. Al, S/S not a problem - well not this particular problem anyway .

Michael

Well if it was a gas issue, it would certainly show up welding the ally and s/s, so it sounds like you're clear there - but still worth checking everything.
The filler wire sounds fine, but to make sure scrub down a length with scotchbrite and acetone it as well.
Does it happen only with a join? what happens when just doing a flat bead without a joint? you could be getting 'suck back' of unshielded weld pool from the back of the weld.
Does this happen only with this particular batch of steel? Have you tried other scrap? It's almost like something is outgassing - like some volatile compound on or in the steel.
What does your tungsten look like after you do one of those welds? Is stuff balling up on it?

Last time I had this issue (comes and goes) I tried running a bead down a piece of steel (no join) and still had a problem. From memory, still had a problem doing that with no filler too.
The tungsten (red band) does not seem to be balling up. Some of the web pages I read talked about too much heat. I didn't have the weld pool any bigger than I needed to - roughly 6mm or so, so I don't think excess heat was the problem. I ground off the TIG welds and ran a stick bead instead - no porosity there (although stick is far more forgiving), so out gassing from the material sounds unlikely. I have a gas lens somewhere. I may have to try that next weekend as I've read that helps. You could be right in that the shielding gas is drawing in something (perhaps moist air?).
It's looking like I need to experiment a bit with cups and technique to see if I can improve the way the gas covers the weld pool.

Michael

Originally Posted by Michael G

You could be right in that the shielding gas is drawing in something (perhaps moist air?)

If the gas line is drawing in air upstream of the torch, then your tungsten will be discolouring/eroding/etc. So have a good look at it.
If it is a case that the gas shield is just not adequate after it leaves the torch, I'd have a good look at breezes, fans, etc. that may be blowing away your shield - check this: http://www.woodworkforums.com/f160/i...0/#post1612826 . A #6 cup with something like 6 lpm of argon should be heaps, particularly if you're a practiced tig welder.

Originally Posted by WelderMick

A #6 cup with something like 6 lpm of argon should be heaps, particularly if you're a practiced tig welder.

Not this little black duck. Check back in 20 years and I might admit to being "practiced" - I've worked around too many good welders to regard my skills as anything beyond beginner level.
I thought you might have it there when I started to read about moving things around as I did that prior to using the machine. In my case it went back in the same place (just swept up around and under where the power supply normally lives), so no joy there.

The electrode is not discoloured or anything, so I don't think I have anything creeping into the gas lines. I was thinking of gas flow not being correct and dragging air in or even gas being blown into the weld if the flow was too much.

The tacks I did before putting down the beads were fine and I seem to recall the first bead was not as bad. Seems to get back to something on/in the material outgassing as the metal heats up. Is there a minimum depth that needs to be taken off black steel before any effects due to skin are removed? As I said before, I cleaned with acetone. My understanding is that it doesn't leave a residue so it should not be causing a problem.

Michael

A couple of suggestions:

1) Check the condition of the insulator between the gas cup and the torch body in case it's leaking, ensure gas cup is done up properly.

2) Try reducing the gas flow in case you are inducing turbulence, are you sure your flow rate metering is accurate? Are you using a pea-shooter type of gauge?

Finally, if you want to try a different welder to eliminate hardware as a cause you are welcome to bring some of the material up here and use my TIG to see if that makes any difference.

By 'practiced' what I was getting at was that you knew the basics of torch position/angle etc. which I think you must if you can do ally and stainless OK.
I fully agree with Gavin's suggestions - worth looking into, although #1 would seem to be less likely if your tungsten is staying clean.
Another thing is that I notice you are getting excellent (full) weld penetration, which leads to another suspect - what is on your welding bench/surface that is directly under the material that you are welding? Is there a possibility that you are drawing in oil or whatever from underneath?
The very first picture you posted - the weld bead is sort of odd for a tig weld - almost looks like you'd expect from a MIG. Do you notice anything untoward when you're actually welding?
Cheers
- Mick

I'll have a look at Gavin's suggestions on the weekend (I don't like trying to weld at night as the contrast causes me problems). The gauge is one of those ball in tube types. It was sold with the welder by a reputable company (WESS), so I can only assume it was decent and reasonably accurate. 8 to 10 lpm is what I was recommended to use. Out of interest, what are others using as a gas flow?

What I was trying to do when I had the problem was lightly fill a joint between some thick pieces of steel that I could then grind flush (or leave a very neat weld bead on). The basic geometry is this -
Scan5.jpg
The welding was on the top, so the table surface (which is Al and while not spotlessly clean is not oily or anything) would not be affecting the weld. Now the interesting part is this - the double lines on the steel are the surfaces that were originally black. All I did was a clean up - say 0.5mm depth of cut to remove the oxide layer, but this is why I'm wondering whether while I've removed the visible oxide there is something in the surface of the steel that is outgassing. One thing I want to try is a piece of steel cut in steps and see whether porosity appears/ disappears at a particular step depth.

The bead in the first picture may have been gone over twice (I didn't think of preserving evidence at the time), so that may be why it looks odd. The top weld in the second picture is more the sort of thing it should be although when that was ground back it had a little porosity in it, although not much. I think that one was the first done. I last used MIG (and only very briefly) around 8 years ago then decided that stick + TIG would do all I needed to do, so can't recall much about it. However, the process did not seem odd at all - no smoke, flames, fumes, sparks, spits, arc pulling to one side, etc. No magnetic clamps either. Occasionally for stick away from the weld but not for TIG work.

Regarding gas flow, I generally use 5-6 lpm for 1F and 1G welds and raise it a bit for out of position welds or corner welds where the gas tends to flow away from the weld area. If I'm running a gas lens I lower the flow rate a little bit.

Originally Posted by Michael G

(But I don't know what)
Any other thoughts on what could be a cause?

Michael

This is what I found in Australian Welding Institute document:


Cavities
According to DS/ISO 6520 cavities are defined as cavities in the weld due to entrapped gases.
Cavities are often found in TIG welds due to the many possibilities for this error to occur.
Error type no. 200
The reason for the formation of porosities can be:
• Lacking or impure shielding gas
• Inadequate cleaning of the groove edges and filler material
• Incorrect adjustment of the flow of shielding gas
• Wrong inclination of the torch
• Wrong size of gas nozzle
• Too quickly an interruption of the shielding gas by the end of a weld
• Draught caused by a wrongly placed exhaust unit
• Leaking hose connections
• Inadequate airing of the TIG torch before welding

Just wondering if humidity causes problems??? Cold metal after acetone evaporation causing moisture condensation on the metal?

PS found this in the DIN/ISO 6520 standard:
2012: uniformly distributed porosity number of gas pores distributed in a substantially uniform manner throughout the weld metal; not to be confused with linear porosity (2014) and clustered porosity (2013)

(can't find a specific cause list for a 2012 yet)

for a good overview: Defects/imperfections in welds - porosity - Job knowledge 42

perhaps a torch tip gas flow meter is a good thing? eg Shield Gas Flow Tester, For TIG, MIG, Plasma Torches [PX-50020] - $15.61 : Arc-Zone.com, The Welding Accessory Experts

MichaelG,
If you're still getting these issues, then you should switch back to another metal (say aluminium) and weld that... obviously if that is working OK then you can eliminate a whole heap of variables in one go - things like gas contamination, gas flow, torch angle, preflow, post flow, contaminated tungsten, gas leaks, fans and breezes, etc. etc. Which would then lead you to investigate the base metal, filler material, joint geometry, etc.
Failing that, you have to take a scientific approach to it and eliminate one variable at a time starting with the likeliest suspects.
Apart from all the suggestions above - your joint geometry is such that hot gasses could become trapped within the space between two pieces of RHS (particularly if it is sealed at the ends) and try to outgas - just one more thing to think about. Any of those abutting faces could have material on them (any paint at all?) that would outgas when hot. I'm sort of clutching at straws now.
Can you do the following a post pics:

- short weld in flat postion - no filler, no joints, just light up the torch and move over the surface of the metal
- same as above, but this time adding filler

Cheers
- Mick

I was planning to do something like that this weekend Mick. (Of course, Murphy's law says it will behave when I try it now...)

Michael

Could it be too much acetone down the crack is not evaporating until heated???