Clients demand clean welds! There may not be any oxygen around the welding zone inside the pipe as this will cause damage to the surface of the material, which will erode faster and provide a breeding ground for bacteria.
The pipes must be able to drain, which is why the weld may not be convex/concave as this leaves product residue at the weld.
The OxyGone welding system makes it easy to meet the requirements! When argon/forming gas is guided in through the pads, the oxygen is pushed away quickly without generating any over-pressure in the welding zone, which makes the weld all smooth and glossy.