Submerged arc welding
An automated fusion process where the arc burns completely beneath a blanket of granular flux. This produces extremely clean, deeply penetrated welds without arc glare.
In submerged arc welding, the arc burns under a layer of powder that protects the melt from the air. This gives you a clean, deep weld without spatter and without glare. The powder partially melts and forms a slag that you have to knock off after welding.
It's important that the powder height and the travel speed are right. If there's too little powder, the arc draws in air and you get porosity. If the layer is too thick, the weld becomes unclean and the slag is harder to remove. The wire must run cleanly centered in the powder bell, otherwise you'll get a one-sided weld.
Make sure the powder is dry. Damp powder gives you porosity in the weld. And if you don't remove all the slag before welding the next pass, you'll get inclusions.