Electroless Multilayer Coatings Used in the Protection of Thermosyphon Economizer from Corrosion

Abstract

Economizers are widely employed in the boiler system to increase efficiency and save energy. However one prominent problem is the severe corrosion of economizer due to the decrease of the exhaust temperature of boiler. Ni–P/Cu/Ni-P multilayer coatings, which could effectively improve the corrosion resistance of the facilities in economizer, are introduced in the present work. The three-layer coatings, whose composition is Ni–P/Cu/Ni-P from substrate to surface, were prepared using dual baths (acidic hypophosphite-reduced electroless nickel bath and acidic replacement electroless copper bath). The corrosion resistance of the coatings was evaluated by porosity and electrochemical tests. The results of porosity evaluation show that all the multilayer coatings performed better than the single-layer coatings of similar thickness. Similarly, The electrochemical tests showed lower corrosion current density for the multilayer coatings in 3.5 wt.% NaCl aqueous solutions.