What's causing this?

[SPARKY]

I've been welding a long time......and this is the first time I've seen this.
All the welds on the one side have this tiny hole at the end of the weld, but the other side does not. I've tried setting the heat higher and lower, as well gas the gas pressure. The material is mild black steel and the gas I'm using is
Argon 75%
Carbon dioxide 25%.

 

[Jmartinez19]

Dirty material maybe. Grind/Flap wheel that oil residue off the tubing and see what you get? Try a back step at the end as well. I would turn down settings a little as well. Just trying to help. Good luck

 

[stjefrey]

Dirty material maybe. Grind/Flap wheel that oil residue off the tubing and see what you get? Try a back step at the end as well. I would turn down settings a little as well. Just trying to help. Good luck

Check your filler metal. I've had spools left out in the open and oxidation can occur.