What is rotpass in welding?

Answer 1

I think you mean root pass. An example would be when butt welding two pieces of plate together (end to end). You would grind a bevel (angle) along the edge of each plate so when you put them end to end there is a small gap between them except at one small point at the bottom. This gap will be filled with molten weld metal to fuse the two plates. Typically, this gap cannot be filled up by one pass with the weld electrode. The welder will go back and forth along the plate eventually filling the entire gap. The "root pass" is simply the first pass the welder makes.