[Shannon]

I've been tasked to weld 3" .065 wall Stainless 304 but have a hard time not overheating the metal. I can't lose the corrosion attributes of SS since this piping will be outside and used for a food grade lubricant. I'm using Lincoln Precision TIG 225 and purging the pipe with Argon. What advice can you offer?

[Otto Nobedder]

I've been tasked to weld 3" .065 wall Stainless 304 but have a hard time not overheating the metal. I can't lose the corrosion attributes of SS since this piping will be outside and used for a food grade lubricant. I'm using Lincoln Precision TIG 225 and purging the pipe with Argon. What advice can you offer?

After your initial heat to begin the weld, you'll likely be around 35A or less for a section that thin. There are several people here who do food-grade work, and will give more specific advice.

I'm going to move your post to the TIG forum, where it belongs, and will see many more responses.

Steve S

[Oscar]

The basic technique is still the same---the weld bead needs to be flooded with argon until the base material has cooled sufficiently to not oxidize in the atmosphere. How long the argon coverage needs to linger depends on your active effort to wick heat away. Use no heat-sinking and you will find yourself needing to run multiple smaller bead lengths to avoid heat build-up while simultaneously needing to use a larger than normal cup diameter. So that begs the question: how are you planning on actively wicking the heat away by artificial means?

[Shannon]

Thanks for your help. I am using a number 8 cup, 1/16" 2% thoriated tungsten and have played with the use of .030 308L MIG wire. I don't have a lot of options for cooling but have tried wet rags wrapped around the pipe near the weld. As long as I get good penetration is a narrow weld bead okay? Also, since the material is so thin, is there a recommended gap between the two pieces?

[Markus]

Hi

- I would try welding with pulse. It will decrease your heat input and when set right you will get at least same penetration. In some cases even deeper.
- Walking the cup also helps on color as your puddle will be longer in argon shield.
- Check that you don't have any leaks in your gas lines etc. Oxygen in shielding gas creates nasty welds!
- Make sure your metal is clean from oils etc.

I do orbital welding on food grade pipes and also on pharma. I wouldn't worry too much about the color on surface, if your machine doesn't leak gas and pipes are clean.

Surface color is just thickened oxide layer that have reacted with oxygen in high temperatures. Nothing else. There are people who say that your weld should be pink after welding, otherwise you have cooked all chrome away. That's is not actually true. Only the surface have reacted with oxygen and lost some of it corrosion resistance, due it's nature of porosity etc.

So how to get rid of that heat tint. There is only two right ways to fully recover the surface. Pickling and electrolyte cleaning. You can always wire brush or grind that surface down and it will help, but on corrosive atmospheres only chemical pickling (or electrolyte cleaning=same principle) will work.

[Markus]

Forgot...

Don't use any gap! You will let oxygen inside the pipe and root will get discolored.

Narrow bead is OK, if there is enough penetration.

In some grades or even between patches you are able to get more penetration with narrower bead. It all depends of the alloying elements and how those change the weld pool flow direction.




Also about those alloying elements.... Some will act more easily with oxygen and therefore those will create darker welds. Molybdenum for example can affect to this.

[Shannon]

Markus,
Thanks for you help, I think that gives me good direction. I know each machine runs a bit different but previously Otto mentioned an amp range near 35, with pulse would I need to bump the amps up a bit and is 20 hz a decent pulse? My machine only pulses up to 20 hz. I like the idea of using the .030 308L mig wire because it allows me to keep the puddle smaller (less heat), is that a proper solution or should I buy some filler wire?

[Markus]

Yup you need to raise amps a bit and I would set lower amps to about half what high amps are. 50/25 Amps for example.
There is many ways to adjust your amps and pulse time. Hertz sucks, because those are so damn hard to get right and adjust the way you want. It will take some to to get use to it.

y5di20Mtlpk

308 mag-wire is suitable I guess, but not sure. If the job is really critical I would buy Tig wire instead.

[Shannon]

Makus,
Thanks for the tips, my parts come in this afternoon so I'll play with the settings and see what works for me.

[Shannon]

Great! Your advice was successful and much appreciated. Good penetration and controlled heat with the pulse. I'm only using a #8 cup so I'm running shorter beads but plan to pick up a larger cup tomorrow. Thanks guys!

[Markus]

Great! Your advice was successful and much appreciated. Good penetration and controlled heat with the pulse. I'm only using a #8 cup so I'm running shorter beads but plan to pick up a larger cup tomorrow. Thanks guys!

Great to hear it worked Add some pics, if possible

[Shannon]

Obviously I need more practice, then again I just started TIG 2 weeks ago. I have decent penetration but need it to be more consistent.

[Rick_H]

Ah..the all mighty tri clover fitting. I weld those daily 316L stainless for Food Grade apps. Typically with a food grade job you would do a autogenous weld (no filler), full penetration with an argon back purge. Using filler is not ideal as you'll have too much reinforcement in the I'd of the piping and that could hold microbes or bacteria.

On .065" wall I'm around 38-43amps (travel speed will alter that), #8 cup, gas lens 1/16" tungs, and no pulse. You should end up fairly smooth inside and out, silver in color on the ID and the outside can be pickled clean.

[Shannon]

That looks great!
Okay, I originally wanted to not use filler rod and wondered if an autogenous weld (i'v heard it called fusion weld?) would be legitimate but was worried it would leave a weak area where the two came together. Using the filler metal adds another factor that could cause problems in the process (for an amateur like me). So if I'm getting a good flush weld inside with the autogenous weld method then it is the preferred way to do it with this material? Outstanding!

[Shannon]

Ah..the all mighty tri clover fitting. I weld those daily 316L stainless for Food Grade apps. Typically with a food grade job you would do a autogenous weld (no filler), full penetration with an argon back purge. Using filler is not ideal as you'll have too much reinforcement in the I'd of the piping and that could hold microbes or bacteria.

On .065" wall I'm around 38-43amps (travel speed will alter that), #8 cup, gas lens 1/16" tungs, and no pulse. You should end up fairly smooth inside and out, silver in color on the ID and the outside can be pickled clean.

What pickling solution have you found works the best?

[Markus]

Good pics

Indeed mostly these welds are made without filler, but sometimes it's needed. Just make sure that your filler won't get oxidized during welding.

On your first picture you have a darker area on 6 o'clock. Is it from tacking without purge? Try to avoid blue color on HAZ. Very light yellow color is still acceptable in most cases and of course perfectly silver is the goal.

Little tip. Always purge as small area as possible and when purging with argon it's good to keep in mind that argon is heavier than air. So tilting pipe a little is very ideal.

[Shannon]

Good pics

Indeed mostly these welds are made without filler, but sometimes it's needed. Just make sure that your filler won't get oxidized during welding.

On your first picture you have a darker area on 6 o'clock. Is it from tacking without purge? Try to avoid blue color on HAZ. Very light yellow color is still acceptable in most cases and of course perfectly silver is the goal.

Little tip. Always purge as small area as possible and when purging with argon it's good to keep in mind that argon is heavier than air. So tilting pipe a little is very ideal.

That may have been the case, should have waited a couple more minutes before tacking. Thanks for the tip on argon. Blue color on HAZ? referring to the inside weld?
I'm not using filler metal for the rest of this project, thanks for the insight guys. I've attached a picture of my first piece without it.

[Rick_H]

With a good purge an inside weld should be shiny silver, no color at all.

I made little purge dams to isolate my area at times, I can post pics tomorrow. The key is your cuts and edges have to be very square, near perfect. I also have a file and such that I only use for my 316l pipe and fittings.

Here's a link I saved from another forum, if you look down you'll see how to make your own purge plugs and damns. Its the 17th one down...
http://www.aws.org/cgi-bin/mwf/board_show.pl?bid=21

[Shannon]

I guess for me the most challenging part is knowing if I'm getting good penetration while running the weld. I'm trying to keep my travel speed as fast as possible while watching the puddle to make sure I don't leave it behind and trying to keep a tight arc with little torch angle. I'm using a #8 cup with 3/16" tungsten at 38 amps, no pulse.

[Rick_H]

Are you making small circles or just a nice steady pull?

[Shannon]

Are you making small circles or just a nice steady pull?

I'm using a steady pull, I worry small weaves or circles slow me down and increasing the heat in the metal.

[Shannon]

Is there a benefit to weaving on this thin wall stainless?

[Rick_H]

Is there a benefit to weaving on this thin wall stainless?

Not weaving but you can do small circles, steady pull or right now I've been playing with some pulse ,2.5pps, 55amps (my maxstar 15O doesn't all peak and background adjustment it is set at 50% each way) I normally weld around ,45amps on .065" wall 316l.

If your not careful with small circles you can overheat but it usually helps beginners assure full pen. Its all is controlling your speed, torch angle and arc length.

[Shannon]

Is there a benefit to weaving on this thin wall stainless?

Not weaving but you can do small circles, steady pull or right now I've been playing with some pulse ,2.5pps, 55amps (my maxstar 15O doesn't all peak and background adjustment it is set at 50% each way) I normally weld around ,45amps on .065" wall 316l.

If your not careful with small circles you can overheat but it usually helps beginners assure full pen. Its all is controlling your speed, torch angle and arc length.

Thanks for the advice, I plan to play around with the settings and techniques.
You guys have been great and very helpful.

[Markus]

Great to hear that you have improved your skills and interested to test new things

Personally I don't like doing little circles on thing walled pipe.
- It's slower
- It easily create too much heat and you end up with concavity
- It usually create rougher bead inside

Do you have TIG-finger? It's very useful on stainless pipes like these. With TIG-finger you can slide you hand more steady than normally and create constant penetration.