So I had an idea that maybe my ugly welds were due to poor electrical contact or some chemical reaction to surface impurities. So I redid the exercise from before where I cut a pipe and then try to weld it back together and make it waterproof.
The difference is that this time I took the angle grinder and really polished all surfaces to a glimmering shiny new-steel surface. That gave a clear improvement! But I also realized that if my current setting was too low, that also caused sputtering and ugly welds. So I turned the current up a step as well, and then I really got things going.
The lower welds came out really nice. The upper ones started off ugly, but then I ground the ugly welds down, and turned up the current. Still not so pretty, but here we clearly have two water-tight welds!
