6 Containers of metal for compressed gas or liquid air, containers of metal for storing acids, tanks of metal, penstock pipes of metal, flanges of metal [collars], balls of steel, tubes of metal, steel tubes, steel tubes, penstock pipes of metal, junctions of metal for pipes; in particular semi-finished products manufactured by centrifugal casting and components of metal, including rings, bushes, pipes, tapers, cones and balls that are unprocessed, pre-processed or processed in accordance with design