But i’m getting RT‑clean roots with no suck‑back using a 70/30 Ar/He mix, 3/32 ER70S‑2, 1/16" gap with a 1/32" land on 10" Sch 80 carbon, walking the cup uphill and backstepping tie‑ins, then switching to a pulsed GMAW fill/cap. Posting because joint integrity has stayed flawless under RT and PAUT across five spools this week, and I’m curious if anyone’s seeing better penetration control staying on pure argon with the same prep.
Tried ‘60/40 Ar/He’ roots — slightly deeper fusion; arc gets twitchy near tie-ins.
Same setup here, and the one thing that killed suck‑back for me was setting a 0.2–0.3 s “downslope” on the machine so tie‑ins don’t yank the root; on smaller bore I’ll drop it closer to 0.1 s.
@OP On 10" Sch 80 with 70/30, I’ve had the best luck running a #10 gas lens around 34 cfh and a 1/8" 2% La tungsten with a about 0.7 mm flat — tames the helium arc and wets the sidewalls. I also keep the arc just a hair ahead of the wire and give the first foot a light 150–175°F preheat on cold spools; without it the bottom can get lazy on fusion. “Short arc, blunt point, big lens” has been the sweet spot for me.
@harrisonx98 I add a brief +10 A hot‑start (about 0.3 s) — steadies the 70/30 keyhole, but watch thin lands…
And i keep arc about 1 mm and 5–7° push on 10" Sch 80; @OP S‑2’s perfect, S‑6 only if scale’s nasty.
I’ve had similar results; a quick 150–200°F preheat and feeding the S‑2 about 35° into the keyhole keeps the root from nosing in when fit-up drifts, and I lightly feather tie-ins so they re-start clean. When I don’t want the extra punch of a hot start, a “0.2 s upslope” does the same job without nipping the toes — tiny preheat is like decaf for helium.