tweake wrote: ↑Thu Aug 05, 2021 11:46 pm i'm not up on walking the cup, but i doubt it would cause that. easy way to test, use clean cups.

just looking back at the other pics, it looks like the black specs are on stop/starts or when going over tacks.

what cup size is being used?

8# ：12*M10

Coldman wrote: ↑Fri Aug 06, 2021 7:24 am What's the wall thickness of the tubing?

mostly 1.5mm or 2mm

what concerns me on the last pic is the heat tint, especially as it seams to be on one side of the weld. that suggests an issue with purging. i usually get spotless back side and i'm crude and rough using a hose and tin foil. may be flow rate or simply not waiting for all the air to clear out befor...

what concerns me on the last pic is the heat tint, especially as it seams to be on one side of the weld. that suggests an issue with purging. i usually get spotless back side and i'm crude and rough using a hose and tin foil. may be flow rate or simply not waiting for all the air to clear out befor...

Poland308 wrote: ↑Tue Aug 03, 2021 6:16 pm It’s possible it’s just silica from filler wire composition.

It is autogenous welding without filler metal

if its carbide, its caused by carbon and oxygen getting into the weld. ie from shielding/purging gas problem, contaminated gas (hence previous mig gas remark), oil on the part, grease/oil on tig torch threads, type of coolant used by band saws. i'm not up on the play with it all, i was hoping some ...

tweake wrote: ↑Mon Aug 02, 2021 4:21 am ok, so its not slag but rather black specks.
that rules out mig gas.
one thing you can try is to see how hard that black speck is. if its super hard it could be carbide.

usually what could lead to black speck？ and is black speck a type of weld imperfection？

You brushed the weld before taking the picture. Hard to tell what's going on when people do that. We are fellow welders giving advice, not the customer....so no need to hide the flaws when you are seeking advice on how to get rid of them. The black spots are oxide deposits that, in your case, are f...

You brushed the weld before taking the picture. Hard to tell what's going on when people do that. We are fellow welders giving advice, not the customer....so no need to hide the flaws when you are seeking advice on how to get rid of them. The black spots are oxide deposits that, in your case, are f...

Hi everyone，just joined and happy to find this forum. please see the attached photos，it is manual TIG autogenous welding on 304 stainless steel， the welds are always with "black slag” which could be grinded off，we do clean the base metal before welding. have you ever met similar problem and wh...

Poland308 wrote: ↑Mon Jul 26, 2021 7:14 pm Are you using an internal purge?

yes

Hi everyone，just joined and happy to find this forum. please see the attached photos，it is manual TIG autogenous welding on 304 stainless steel， the welds are always with "black slag” which could be grinded off，we do clean the base metal before welding. have you ever met similar problem and wha...