This paper focused on the corrosion resistance of cold spray Al–Al_2O_3composite coatings used on carbon steel pipe surfaces under thermal insulation. Al–Al_2O_3coatings 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-Al_2O_3 was added in spraying powder, the coating could obtain higher hardness and a denser microstructure. From corrosionunder-insulation(CUI) tests, Al–Al_2O_3CS 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-Al_2O_3 might bring any negative effect on corrosion resistance. Al–Al_2O_3CS coatings were sensitive to the chloride ion concentration. When these coatings were exposed to higher concentrations of NaC l, the coating’s exhibited faster degradation. This paper focused on the corrosion resistance of cold spray Al-Al_2O_3composite coatings used on carbon steel pipe surfaces under thermal insulation. Al-Al_2O_3coatings were produced on the carbon steel pipe surface by cold spray (CS) technology. corrosion resistance of coatings beneath mineral wool insulation is isothermal, thermal cycling and wet / dry conditions. The results was that when α-Al 2 O 3 was added in spraying powder, the coating could obtain higher hardness and a denser microstructure. ) tests, Al-Al_2O_3CS 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-Al_2O_3 might bring any negative effect on corrosion resistance. Al-Al_2O_3CS coatings were sensitive to the chloride ion concentration. When these coatings were exposed to higher concentrations of NaCl, the c oating’s showing faster degradation.