The pipes for residual gas are arranged on either side of activated carbon filters and are used to transport gas or liquid. In the current project, landfill leachate is filtered and both fed and drained into the public sewer system. The inside of the pipes must be precisely continuous welded, as back-welding is not permitted due to the small diameters. Also, as the media is sometimes unknown, full-immersion pickling is essential for corrosion protection.