Feedback on weld please

[weldy]

The weld is on 304 SS 1.5mm thickness, 1.6mm tungsten with 1mm filler. Backpurged with argon. I haven't welded much before, a couple of times and this is the first one in a while. Colour of the weld to me is a bit grey however if I don't use any filler and weld autogeneous then the colour is a nice purple/gold colour.

Roughly 25amps on the welder,about 2 sec upslope and about 4 sec downslope with a postflow of about 5 secs.

Any comments and tips will be appreciated. Thanks Andy

 

[backpurge]

That's looking good for early attempts, you could maybe travel a bit faster and use a little less wire but you are well on the way.

A good cheat to make it look prettier is to give the weld a good wire brush to get all the oxide off then weave over the top with around the same power of it without any wire, this should blend it all in quite nicely

Any chance of cutting it open so we can see inside

 

[Delgado]

Not looking too bad in places, try turning the amps up and going faster. You want about 33amps without filler and 37/39amps with filler for that thickness material.

 

[weldy]

Ok I will up the amps a bit more and try and travel a bit faster on the next part. Is there any reason for the grey looking welds? I have backpurged with about 10lpm for the first minute then turned it down to about 3lpm during welding. All cleaned with acetone before welding too.

I have attached a picture of the inside as best as I could- they are two 45 degree bends so it is difficult getting a good view in there. I haven't penetrated much on the inside, only in a few places, I guess because the amps are too low. I will turn it up on the next pass and see what the penetration is like then.

Thanks Andy

 

[backpurge]

The grey surface of the weld is surface oxides, not easy to avoid but getting the heat input down as much as possible will help, it's nothing to get overly concerned about unless you are doing high quality work
Hard to see what is going on with the penetration bead but it looks like a lot of oxidation and not much penetration but can't be sure from the photos, on short runs of pipe you should be able to achieve this sort of finish

And with a change in backing gas you can get to this standard

 

[weldy]

Thanks backpurge- when you say a change in backing gas what exactly do you mean? I am currently using the same argon used to weld with. As for the penetration I don't think it has penetrated fully so would you suggest upping the amps? I think I was trying to keep the amps down to avoid discolouration so maybe it is too low.

Regarding the purging and oxidation on the inside, what purge rate would you normally purge at and for how long prior to welding? Maybe I need to purge it a bit longer. Thanks

 

[backpurge]

Both welds were done with a residual oxygen level of around 40ppm, the first one was done using argon and the second one was done using 10% hydrogen in nitrogen.

To get the penetration through you need to up your amps, to start off with I wouldn't bother adding any filler until you are getting full penetration all the way round, on a square edged joint in 1.5mm wall thickness tube you shouldn't need filler anyway, just fuse the edges together

Can't really be specific about pre weld purge times as it changes from job to job, the flow rates don't sound to be a million miles out but how are you blanking the tube off and how big is the purge gas exhaust hole

 

[weldy]

Ok I won't add any filler on the other joints and just go for full penetration instead. I am blanking one end off with foil masked up and with a hole at the top the size of the filler rod to allow the oxygen out. Other end has the argon feed and again foil capped and taped.

Just did the two welds below now onto a flange. Didn't use any filler this time and upped the amps a bit to about 35ish and went a bit quicker. Seems to always be a much nicer colour when not using filler. Do you normally clean the filler rods or do anything special to them before using them? I clean the rod with some acetone but that's it. I can only presume it is the filler that is causing the different colour.

 

[Delgado]

I think I was trying to keep the amps down to avoid discolouration so maybe it is too low.

Regarding the purging and oxidation on the inside, what purge rate would you normally purge at and for how long prior to welding? Maybe I need to purge it a bit longer. Thanks

Welding Stainless with low amps and slow travel speed is a mistake, you would think that less heat would be transfered but actually it's the opposite. The 'colours' on the weld are caused by the hot weld deposit reacting with the oxygen in the air as it leaves the sheilding of the argon gas (gas lenses can help with this). The slower you travel the more heat you put into the material and the longer it stays hot (due to thermal conductivity), causing it to change colour. The different colours depend on its temperature when it reacts with the air, from silver to straw,brown, blue, purple, grey, then black. The colour of the root depends on how much O2 is present in the purge, again ranging from silver to black.

The purge rate/time depends on the size of the area you want to purge (there is a formular to work it out, but I can't remember it off the top of my head), and if it were critical then an o2 meter would be used. For what you're doing, crank it up to about 12lpm for a few minutes, then turn it down to about 4lpm, and hold a lighter to the vent hole (a 6mm hole), if it wont hold a flame then you're good to go. Also, check that when you operate the torch it isn't detracting from the purge line flow, as this can also be a problem with the setup you're using (easily remidied by using 2 flow meters and a 'Y' fitting).

Here's a link I've lifted from UKW that tells you pretty much everything you need to know about welding Stainless.

 

[backpurge]

While ever stainless steel is above about 200 deg c it will start to oxidise when it comes into contact with the oxygen in the atmosphere, this is why highly reactive materials such as titanium etc are sometimes welded in a bubble filled with argon
When you are TIG welding using a filler you are generally producing a bigger hotter weld pool which takes longer to cool down, especially when you are learning, as you will have a tendency to feed too much filler into the weld pool the secret is tiny dabs of wire at regular intervals and this will lead to a more oxidised weld. The surface oxide is easily removed by wire brushing
The welds above may look cleaner but they also look very concave with virtually no throat thickness to them, you need filler in these to improve the weld strength
For your purging set up, if you are using tape you need loads of holes like you described in the exhaust end (like a pepperpot) to allow the gas out, if you can, stand the pipe on end so you are filling with argon from the bottom and venting the exhaust from the top and use a low flow rate so you don't cause any turbulence in the pipe and just experiment with the amount of time it takes to gt the result you want

 

[backpurge]

Delgado is spot on, was still typing my reply while he posted his otherwise I wouldn't have basically repeated what he said

 

[Delgado]

Cheers, although I think that you also added some good points with your reply.

 

[weldy]

Thanks for the information guys. I agree the last pictures I attached looked nicer but the welds are concave like you said. I would normally use filler when welding a flange onto the pipe but tried it without. I will do another pass with some filler to strengthen it up.

I will try the method you stated about filling with argon at the bottom and venting at the top although with the longer length of pipes this is a bit more difficult with the space. I will also put some more holes in the end to improve the exit of the oxygen. I have a y fitting on the tank and a flow meter on each pipe to make sure the purge line isn't drawing all the argon when the torch is on.

I guess I will cut some sections of pipe off into about 2 inch lengths and experiment until I get the result I want and full penetration on the inside.

Thanks for the information and feedback. Andy

 

[hotrodder]

Pretty much all been said but there's some more tips on purging in this thread... http://www.mig-welding.co.uk/forum/showthread.php?t=12621&highlight=purge. As said a lighter/match works OK as a basic test of the purge exit but be aware that a flame will be extinguished long before the O2 is in the ppm range and of course can simply be blown out if the flow rate hasn't been turned down enough...
Another rule of thumb for those of us without an O2 meter is to have a min of 6 volume changes before striking an arc.

Regarding the welds with filler... again as said typically have more heat input compared to autogenous but if the end of wire is withdrawn too far (i.e. removed from the gas shield) the end will oxidise only for those oxides to end up in the weldpool next dip of the wire...

Probably already aware of this but if you cut up a bunch of 2" long sections to practice don't go mad and weld 'em one after the other as the heat soak will quickly make it impossible to get clean results

 

[weldy]

Thanks hotrodder. I might look into getting a larger ceramic, currently using a size 6 but i would like to get the large collect and gas lens to get more coverage of the weld and filler.

As for the practice welds on the 2 inch sections, I was only going to weld two sections together and then move onto another two, not continually welding another section on.

What I do find though is that when I take my finger off of the trigger on the torch and finish the weld that I always seem to end up with a tiny crater. I have upped the downslope and post flow to try and change this but i still seem to get it. Is there any reason for this? Also, when I stop the weld and it is on the downslope, is it better to keep the arc fixed on the same point or continue to move it along?

 

[hotrodder]

If the end/crater amperage is too high then more downslope time won't help much i.e. you want the weld to freeze during slopedown. Keeping the arc moving will help regardless, as the pool freezes can continue moving forward or stop and make small circles as the arc winds down.

 

[Delgado]

What I do find though is that when I take my finger off of the trigger on the torch and finish the weld that I always seem to end up with a tiny crater. I have upped the downslope and post flow to try and change this but i still seem to get it. Is there any reason for this? Also, when I stop the weld and it is on the downslope, is it better to keep the arc fixed on the same point or continue to move it along?

When welding anything round, run the end of your last bead over the start of your first one (looking at your fisrt Photos you're not doing it), then finish your weld as Hotrodder suggested. This will give you a nice clean join in the root profile and will virtually eliminate any chance of pin holes, being as you're not just melting through the tube, but the thicker profile of the weld bead as well (which as you tail off wont penetrate all the way through).

If you're not using filler and the heats right craters shouldn't be a problem, if they are then dab a little bit if filler (which you should always have in your non welding hand, even if you're not using it) in at the end as you start the slope down, again, finishing up in the ways suggested.

 

[backpurge]

Another tip re crater filling is to practice getting a dap of filler in just as you start your downslope, it's all about trying different downslope times etc
Does your downslope fade away to nothing or can you pre set the finishing current?

 

[weldy]

Ok I will give that technique a try then to eliminate them. The downslope on my tig I believe fades away to nothing. It is a r-tech TIG200PDC:

http://www.r-techwelding.co.uk/welding_equipment/Tig_Welder/TIG_Welder_R-Tech_Tig200PDC

Thanks for the tips, I will continue today practicing.

 

[Delgado]

Ok I will give that technique a try then to eliminate them. The downslope on my tig I believe fades away to nothing. It is a r-tech TIG200PDC:

http://www.r-techwelding.co.uk/welding_equipment/Tig_Welder/TIG_Welder_R-Tech_Tig200PDC

Thanks for the tips, I will continue today practicing.

Your machine should be fine. For what you're doing I'd set the upslope to about one (if at all), the down slope to about 3 or maybe 4 and the post flow to 4 or maybe 5, but others may use different settings that work for them.

Just noticed that you're just down the road from me, obviously it's alot easier to show you all this stuff than try to explain it over t'internet, so if you ever want any pointers PM me.