Stainless Tubing Help

[Injected65]

I am working on my first project using 304 Stainless tubing. The tubing that I am working with varies in diameter from 1.75" to 3.5". All of the tubing is around .065" thick. Most of the joints are butt welds and I have been trying real hard to keep the fit up tight. The problem I am having is the welds end up with little to no color. They look grey and dull. During my many hours of practice, the only time I seem to be able to get a nice looking weld is when fusion welding the tubing. As soon as I add filler the weld turns grey.


200DX welder
#8 Gas Lens
Tried 30-70 amps with the sweet spot around 50 it seems
Also tried with pulse and without.
Gas flow around 7-10 L
Tried with back purge and without back purge with no noticeable change
Tried 1/16 tungsten and 3/32 tungsten. 3/32 seems to have a more stable arc
Tried 2% Ceriated, 2% Thoriated and bought but haven't tried Lanthaniated Tungsten.
Have been using .045" 316L filler rod


I'm just getting frustrated with the lack of improvement on the welds. I have had no problem with steel or aluminum, but this Stainless is kicking my butt. I really would like to be able to get a nice looking strong weld. I forgot to grab my camera from home. I will post up some examples of the welds tonight.

Thanks for the help,
Chris

[Paul Moir]

Grey is the result of too much temperature when the weld moves out of your gas shield. That's easier to achieve when fusing because you're moving faster and using less heat. (I also suspect that you get some from the rod itself by moving it out of the shield.) Doing tubing is particularly difficult because maintaining your torch angle & back shielding is harder. And I have noticed that 316l filler seems to be more difficult to keep pretty than 308.

But really I don't care. Grey doesn't make your welds weak since it's just the surface that's affected, and I pickle my welds so the colour is gone anyway (and the corrosion resistance lost is regained; the free iron is removed from the surface).

EDIT: it's hard to loose heat out of your stainless because it's such a good insulator compared to steel (about 3x!) or esp. aluminum.

EDIT 2: If pretty colours is part of the spec, think big cups, lots of gas, short welds with lots of cool down and/or some way of soaking the heat out of the stainless.

[sportbike]

Not sure what you are stating with, "The problem I am having is the welds end up with little to no color." The welds aren't supposed to have color. Color is the result of oxidation.

If you aren't seeing any difference with back purge or no back purge, something may not be correct. When welding thin wall stainless tube, a sugary "clumping" will apear if you don't back purge or otherwise protect the backside from oxidation.

This is an odd question, but are you sure it is in fact stainless and not plain steel?

[Injected65]

By color I mean this nice golden hue to the weld. Similar to these pictures I found on the net.





The back purging does make a difference on whether or not I get sugaring on the backside, but it does not seem to effect the color or look of the weld its self on the front side. I've made the move from a regular style cup to the gas lens and then moved up from a #5 to a #6 to a #8 to make sure I have adequate gas coverage. I've also had the gas as low as 5L and up to 15L before and it didn't seem to change anything. Torch angle has been anywhere from straight 90* to the work piece to 45*. I've made sure to not pull the filler out of the gas flow as well. To give you a reference, I've gone through most of a 250cf tank of gas as well as nearly 1# of filler rod testing out different variables trying to get not only a strong joint but a visually nice one as well.

Sportbike - Yes the tubing is definitely 304. It has the spec printed right on the tubing. The filler rod came out of a brand new box at the LWS.


Thanks for the help guys. I'm sure the problem is something I am not doing right. I'm just looking for ideas on other things to try to see what is happening here.

[jerky]

i also suggest using 308L filler. this is a better match for 304L.

[jakeru]

Paul Moir has nailed it. Grey welds are from the metal being too hot when they leave the inert environment.

You should be able to easily eliminate the dull grey at least at the end of your weld, just by increasing your post-flow and/or by not pulling away from torch from the weld area so fast. Keep the gas flowing as long as it takes for the metal to cool down.

As for getting the whole weld bead to not be dull grey, you might need to develop better torch and filler feeding coordination. Using the right torch angle is also important. Specifically, try to use less torch angle (closer to perpendicular with the surface your welding) to push the inert gas backwards over the hot metal. If you angle it too far, the inert gas won't get pushed backwards enough. Another fact is that Argon is heavier than atmosphere and sinks, so you may get better results in some positions than others. (e.g., flat welding easier than vertical welding.)

Check out the video in this thread if you haven't already, it shows .065" stainless exhaust tubing being welded with great technique and results:
http://www.everlastgenerators.com/fo...-Welding-Video

[Injected65]

Great video. A couple of things I noticed were that the tungsten in that video was ground with a bunch more taper than what I have been doing. I'm going to watch that video again tonight and try it again with reground tungsten, greater post flow time and I am also going to work on the purge setup to let it purge longer before starting my weld. Hopefully this is the key to getting a nicer looking weld.