Apparatus for coating a metal gas-pressure bottle or tank

An apparatus for the internal coating of a pressure tank adapted to contain a high-purity gas at an elevated pressure and wherein said tank is composed of metal, is closed at a lower end and has a narrow mouth at an upper end formed with a screwthread, said apparatus comprising:

• a plug sealingly and removably threadedly engageable with said mouth to close a chamber formed within said tank so as to enable said chamber to be evacuated to a vacuum of a pressure of at most 10.sup.-5 torr;
• means on said plug communicating with said chamber and coupled with a vacuum pump for evacuating said chamber;
• an electrode mounted on said plug and reciprocatingly displaceable into and out of contact with a wall of said tank in said chamber repetitively to strike electric arcs between said electrode and said wall;
• and
• an electrical source connectable between said tank and said electrode to supply electrical energy for said arcs, whereby said arcs after being struck travel along said electrode and evaporate material therefrom to coat the interior of said tank at least in part with said material.