Investigation of corrosion and fouling resistance of Ni–P-nanoparticles composite coating using online monitoring technology

When the temperature drops, industrial flue gases (fly ash and corrosive gases) are condensed on the surfaces of heat exchangers and easily cause operational problems such as fouling and corrosion of heat exchangers. In the present paper, an online monitoring system is established to experimentally investigate the heat transfer, fouling resistance, and corrosion resistance of different materials in coal-fired boilers under low-temperature ash deposition and dew point corrosion. The materials include ND, 316L, 2205, Ni–P, Ni–P-PTFE, Ni–P–SiO2 (50 g/L silica sol), Ni–P–SiO2 (60 g/L silica sol), and Ni–P–SiO2 (70 g/L silica sol). It was found that Ni–P coating is excellent in anti-fouling performance, and Ni–P–SiO2 coating excels in corrosion resistance. Also, the coated tubes can significantly decrease the fouling phenomenon. Comparing the electrode potential, corrosion rate, and surface morphology reveals that the tested materials can be sorted in terms of the corrosion resistance as 2205 > 316L > Ni–P–SiO2 (50 g/L silica sol) > Ni–P–SiO2 (60 g/L silica sol) > Ni–P–SiO2 (70 g/L silica sol) > Ni–P > Ni–P-PTFE > ND. Note that the performance of Ni–P–SiO2 (50 g/L silica sol) and 316L is very close. Therefore, the application of coated tubes in heat exchangers helps recover waste heat from coal-fired boilers, improve heat transfer efficiency, extend the service life of heat exchangers, and save costs.