ArtMetal

TIG welds are beautiful when everything works right! Here are some things to check to solve the problem!

The alcohol cleans off any grease but not the oxides on the surface. You need to remove the oxides with emery cloth or some other abrasive. And if the end of the tube has a burr when it was cut, scrape off the burr with a carbide scraper. Oxides and cutting fluid can be left there. Also when you wipe on/off the alcohol, the cloth leaves bits of material on the burr. This can make pitting too. Clean inside and outside the tube to at least a 1/2" on either side of weld.

IF you are welding the steel with no filler rod, it is especially important to remove the oxides before welding. Filler rod material has deoxidizer in it (ER70S-6 used for oxyfuel is also used for TIG and has high silicon to deoxidize and make the weld pool more fluid).

With this thin wall, you are probably not using filler.

Other things to check:
If there are loose connections or pin holes in shield gas lines, air will aspirate into the line.
Make sure the torch angle is not too flat (should be 18-20 degrees off the vertical) and it is not too far from the metal.

The tungsten stick out (from the cup) should not be more than the internal diameter of the cup (unless you have a gas lens, which is like a screen or faucet washer in cup). If angle or stick out are excessive, the weld pool is not protected from the atmosphere.

Rarely, but it is possible: the argon in the cylinder can be contaminated. Don't pounce on this as your first possible cause. But if your shield gas supplier does not adequately purge the lines between mixing shield gas (such as the 75-25 argon Co2 mix for MIG), there won't be 100% argon.

Of course, the tungsten needs to be ground of any contamination from previous welding foibles, and the machine set for DCEN and a high frequency start so you do not have to scratch start the arc.

Let me know which one of these fixes the problem or if it is something outside of this list!