Abstract: An evaporator adapted to convert a liquified gas, such as chlorine, into a gas, the evaporator including an enclosed vapor chamber functioning as a pressure vessel. The vapor chamber is suspended within a water chamber having a heater serving to raise the temperature of the water to a level at which heat transfer through the wall of the vapor chamber causes the liquified gas fed therein through an inlet pipe to evaporate and produce a superheated gas that is discharged through an outlet pipe. The vapor chamber is fabricated of a steel tank whose outer surface is coated with a film of tetrafluoroethylene having a thickness just sufficient to render the film impermeable to water, thereby inhibiting corrosion of the steel surface and the formation of scale thereon, the thickness of the film being insufficient to materially reduce the heat transfer characteristics of the vapor chamber.