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.