A relatively small enclosure approximately 12' wide and 10' long and about 8' high where external welding machines are mounted and carried from one joint to the next by a back end rig.

The shack typically is a lightweight metal frame covered with thin sheet metal. A shack will have a special floor designed to pivot up to allow the shack to be lowered onto the pipe and then pivot back down to allow easy access to the pipe. Shacks provide the welder lighting and protection from the elements.