That is, the "Wurzellage" is the root pass or penetration pass and the "Stützlage" is the second pass, the one that comes after the root pass for reinforcement.

As you can see for yourself in this telling example:

Can you explain single pass and double pass welding?

Sure. We use both. A single pass weld is usually done where the weld bead does not have to be large or super strong. We use that for small parts. On the bigger joints, you may need a root pass for proper penetration and strength. Then you use a finish bead, or dress bead, to complete the weld, which is a standard welding practice whenever you have a large part that requires a high-strength weld.

The first pass is for penetration, and the second pass is the remainder of the joint fill, because you can't fill it all at once. If you try, you are going to burn through--undercut--or not get enough penetration because you have to move too fast to avoid burning through--all sorts of problems. The root pass and the finish bead are the way to go, definitely.

http://www.merlinbike.com/english/tech/welding.html

V

Referenzen:

www.merlinbike.com/english/tech/welding.html
www.crms.uky.edu/welding/index2.html