Improvement of corrosion resistance of internal surfaces in power-generating equipment

Abstract

We investigate the possibility of using induction currents for improving the reliability of thermal power plants by increasing the corrosion resistance of internal surfaces of power-generating equipment, such as heating surfaces of boiler units. Corrosion resistance can be enhanced by improving the strength of an oxide film formed during passivation (oxidation). In this work, the oxide film strength was increased by electrochemical passivation of metal surfaces with induction currents. Using the method of multidimensional mathematical modeling of multi-parametric and multi-functional processes, we established that, for a continuous-loop economizer of a steam boiler comprising steel pipes with an inner diameter of 32 mm (24 coils operated simultaneously), an aqueous oxidant (oxygen) solution should be passed through the entire system of pipes for 4 h at an alternating current of 25 A. Under this treatment, oxygen should be added into the aqueous solution at a temperature of 130–450°C, an oxygen concentration of 1 g/kg, and a water flow rate of 0.5–5.0 m/s. Treatment intervals should be determined depending on the operating conditions of the equipment: reset, shutdown, or preservation. The efficiency of the method depends on the electric current passed over metal surface, treatment duration, oxidant concentration, as well as the type and size of the treated metal surface. The proposed passivation method can be used in both drum boilers and single-pass boilers. For example, it is recommended that passivation of water walls be carried out during boiler warm-up operation at 30–40% of boiler load, as well as passivation of superheat surfaces of boiler units and economizers. Therefore, the use of electrochemical passivation can increase the corrosion resistance of metal surfaces of power-generating equipment at thermal power plants.