[Brett Henderson]

Hello, i need some pointers for tigin 6g pipe. I do good on root and hot pass but on cover pass i cant keep the under cut out when walking the cup.. im welding with my tig machine set on 100-115. I thi k im getting it to hot after root i let it cool befor thehot pass n then weld on out after that... getting way to much under cut but only on top side

[Coldman]

Undercut on tig caps is usually underfill not undercut. Push more wire into the puddle should fix it.
Also you don't say what size or schedule pipe you are welding so I can't comment on amps.

[Poland308]

Try letting the pipe cool down till you can touch it with a gloved hand. Then turn down to about 80-85 amps with a 3/32 wire for the cap. I'm assuming it's carbon pipe and that your running stringers for the cap. If you are you should space out for a minimum of three stringers on sch 80 and more like 4 or 5 on the super coupon.

[Rick_H]

I typically increase each pass to ensure proper tie in/wet out. I do however agree with if the cap in undercut it usually is due to not enough filler being pushed in or your torch angle when walking, you just want to nip the edges to ensure they get broken down.

I increase around 10 amps per pass, all stringers on cap run same amperage....amps will depend on speed. My root is usually 85, hot pass 95-100, cap 105-110, sch 80 carbon pipe, 3/32" tungsten, #8 cup (usually a GL), 3/32"-1/8" filler, 37.5" degree, 3/32-1/8" gap...dependent on WPS.