[sschefer]

Hey guy's Dustelf is right, those weld craters will form cracks and if you look a bit closer, the welds are also contaminated and porous.

[anthonyfawley]

A good weld could be ugly.. but more importantly a good looking weld could also be dangerous

[BLAZO]

Hi bro. I would preheet 3 mm plate and then weld them together. It will lower the gap of melting point.
Sorry for my bad English.

[racingparts]

i'm starting to think that preheat is the only way to go
i'll give it a try, and lower the amps in order not to blow the pipe that melts instantly otherwise