Metallurgical question: What is actually happening to the metal as it is fusing? I know that at least with iron, when it cools quickly from a liquid state its grains naturally form in a brittle state and that filler metal additives offset this, but besides that, I know nothing.

Its not for a job, I'm learning to weld in high school. I have been through open root stick, tig, and mig on plate but pipe is a whole different deal.

Yep, it is structural code.

Is a 3/32 for the hot pass what D 1.1 code wants?

The land is supposed to be 1/8 and the root opening is supposed to be 3/32. Land goes back and forth and root opening is usually a little wider.

This is my first post on the forum, so bear with me... I have started welding 5G 6 inch ID 40 wall pipe, with a 6010+++++ for the root and 7018 the rest of the way. The root pass is fine for me, but I have trouble with tons of slag in the toes of the hot pass. Any advise on this? Thanks for your tim...