[ShinySSguy]

It's been a long time since I welded SS & I'm relearning, mostly by trial & error. Working on 0.065" wall 316L polished stainless tube, doing fused butt welds with 100% argon back purge. Running 43 amps with a foot pedal at full power. Sending about 15 CFH to the torch & purging at about 12 CFH. Keeping the torch stationary at 90º to the tube & slowly rotating the tube by hand. Penetration is good with complete fusion inside & out. However, the exterior weld has a dull, dark grey appearance & no amount of polishing will clean it all up. (I could pickle it out, but shouldn't have to.) There's also a little bit of undercut at the margins of the weld. On the interior, the weld color is gold, but the surface is dull like the outside... almost looks like very fine granules or crystalline.
Any help in troubleshooting these issues is greatly appreciated!

[RamboBaby]

This looks like a post for Rick_H. He helped me to get my first good looking stainless weld on super thin 16 gauge SS. He has a ton of tricks in his bag.

[LtBadd]

Hey SSguy, welcome to the forum
What diameter tube are you welding?
The dull gray is from a lack of shielding, you don't say if you're using a gas lens but you need to be, also I would suggest the large diameter gas lens such as the CK model with the #12 cup.

The pic below is for the #2 series water cooled torch, FYI

ck gas lens.jpg (30.36 KiB) Viewed 791 times

[ShinySSguy]

This is 2" OD tube. I'll definitely switch to a bigger cup right away. Gas lens is on my wish list as soon as I have a few spare bucks. In the meantime, I'll try a couple layers of fine SS mesh around the collet body for a quick & dirty upgrade.

[Exotic metals]

The dull gray could be to much heat,,,,another thing to watch for is pre flow. Make sure the area is purged of 02 before you strike the arc, As was stated large gas lens, don't piss around, weld and keep moving keeping that filler rod in the gas. I use a lot of copper as backing behind my stainless if possible, tubing,,,,purge the hell out of it! Have fun!

[Rick_H]

The amperage range can work but you need good gas coverage or they tend to turn out grey, however usually brush clean. I prefer to weld a little hotter and faster.

With my sanitary stuff 1-3" I run a CK jumbo cup (1-1/8") 1/16" tung, 60amps pulse 2.5pps, 50% peak 50% background, full penetration. If I don't pulse I'm around 48amps usually, put the welder in 2T so it tapers off (Maxstar 150sth). Once the puddle is established and I see the "devil's eye" I know I have full pen and I start moving, I rotate the pipe by hand at times as well but most of the time I'm welding out of position and don't have that luxury. I usually purge with 20cfh depends on the run, then turn it down as I get closer to the last joint, run about 25-30cfh on my cup....it will brush out or scotch brute belt polish mirror finish. Can you post a photo or two?

If you have undercut, I would check fitup and or turn the purge up a little....fit up is everything.

[exnailpounder]

Hey Rick...those 347 rods are on the way...they went out Saturday.

[Oscar]

Use braided copper wire (at least 1/2" wide) and wrap it tightly around the tube, on both sides of the seam about 3/16-1/4" away [from the seam]. Wrap it so that the braid ends up being at least 1/4-3/8" tall. This will help draw out the heat the same way copper chill blocks do for flat surfaces. If it works on titanium, it will surely work on SS. Plus it's cheap too. A 25' roll on ebay is likely less than $20.

[ShinySSguy]

Thanks to all for the great tips! I really appreciate the help!