HEAT-TRANSFER PIPE FOR FEEDWATER HEATER, FEEDWATER USING SUCH HEAT-TRANSFER PIPE AND METHOD FOR MANUFACTURING SUCH HEAR-TRANSFER PIPE

摘要

PROBLEM TO BE SOLVED: To effectively restrain the elution of chromium by composing a heat-transfer pipe of stainless steel containing chrome and forming a nickel ferrite oxide film with a specific on the surface of the heat-transfer pipe. SOLUTION: A gas 5 as a treatment medium is fed from a supply pipe 3 by placing a hollow pipe that is formed through such processes as dissolving, ingot-making, rolling and pickling with stainless steel containing chromium and a heat-transfer pipe 2 in an electric furnace 1. In other words, the temperature in the electric furnace 1 is set at 220 deg.C or higher inject the gas 5 (for example, air) whose oxide concentration is 20 to 100% from a gas inlet 3a and effuse the gas 5 from a gas outlet 3b. The effused gas 5 is continuously or intermittently supplied to the inner and outer peripheral surfaces of the heat-transfer pipe 2 whose surface is treated in the pickling process. As a result, an nickel-ferrite oxide film is generated on the surface of the heat-transfer pipe 2. The thickness of the film is set at 0.01 to 5 m. If the thinner than 0.01 m, in this case, the effect of the restraint on the elution of chromium is insufficient. If the thickness is 5 m or thicker, it takes excess time for treatment because the thickness includes an unnecessary part. An especially effective thickness is 0.1 to 3 m.