Corrosion performance of Al–Al₂O₃ cold sprayed coatings on mild carbon steel pipe under thermal insulation

This paper focused on the corrosion resistance of cold spray Al–Al₂O₃ composite coatings used on carbon steel pipe surfaces under thermal insulation. Al–Al₂O₃ coatings were produced on the carbon steel pipe surface by cold spray (CS) technology. Experimental apparatus was built to test the corrosion resistance of coatings beneath mineral wool insulation under isothermal, thermal cycling and wet/dry conditions. The results showed that when α-Al₂O₃ was added in spraying powder, the coating could obtain higher hardness and a denser microstructure. From corrosion-under-insulation (CUI) tests, Al–Al₂O₃ CS coatings were proven to be efficient in protecting carbon steel pipe from CUI mainly owning to lamellar microstructures of coatings. There was no evidence to show that α-Al₂O₃ might bring any negative effect on corrosion resistance. Al–Al₂O₃ CS coatings were sensitive to the chloride ion concentration. When these coatings were exposed to higher concentrations of NaCl, the coating's exhibited faster degradation.