Orbital Welding is one type of welding where the welding arc is mechanically rotated around a static work piece continuously. Orbital welding can be used on welding pieces that would be very difficult to weld manually, such as pipes. This is an ideal welding technique for use on items where a strong weld is hard to achieve due to welding positions and size. Orbital welding machines use the Gas Tungsten Arc Welding application and rotates a welding arc from a tungsten electrode around a tube-weld joint.
Also, If you're interested in orbital welding, see this instructable to learn more:
This is a basic guide on how to weld using Orbital welder 180SW.