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 surfac...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.展开更多
The corrosion under insulation dominates metal loss in the case of API （American Petroleum Institute） 5L Grade B geothermal pipeline, whereas, the other possible corrosion causes, such as stress corrosion and therma...The corrosion under insulation dominates metal loss in the case of API （American Petroleum Institute） 5L Grade B geothermal pipeline, whereas, the other possible corrosion causes, such as stress corrosion and thermal cracking, did not serve a role as critical factors regarding to pipeline degradation during 26-years working operation. Actually, the header pipe diameter 32 inches and 40 inches require priority for inspection due to higher corrosion rate compared to smaller pipe diameters. By simulation method on similar heavy duty service condition in which the working pressure of 15 bars and temperature of 183 ℃, it was proved that corrosion rate will severely occur at corrosion rate more than 10 mpy in the pipe diameters of 20 inches, 32 inches and 40 inches. Further,condensation factor may contribute more significant in the case of corrosion under insulation. Practically, the metal loss at a half initial thickness requires priority for inspection, intensive maintenance or possible partial replacement.展开更多
In-situ tests and numerical manipulations were conducted for comparison of superior/inferior quality of casing-tube-vacuumized insulation and polyurethane insulation of fi＇eezing apparatuses in relation to non-unifor...In-situ tests and numerical manipulations were conducted for comparison of superior/inferior quality of casing-tube-vacuumized insulation and polyurethane insulation of fi＇eezing apparatuses in relation to non-uniform cold distribution in the multi-coil fi＇eez- ing layout and the contradiction between large-coil diameter layout of the freezing holes and stability of the headfi＇ame base. Tests show that： （1） under current technology, vacuumized insulation is of short duration due to lack of appropriate applied vacuum; （2） after the freezing pipe is insulated with polyurethane, the temperature gradient is less than no insulation, and the temperature dif- ference between insulated and non-insulated apparatuses is stable as the freezing period increases. Finally, it is pointed out that polyurethane insulation is quite efficient in present technical freezing construction. Keywords： freezing pipe; insulation effect; polyurethane; energy conservation展开更多
基金Supported by innovation program for graduate students in Jiangsu Province of China(CXLX12_0434)
文摘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.
文摘The corrosion under insulation dominates metal loss in the case of API （American Petroleum Institute） 5L Grade B geothermal pipeline, whereas, the other possible corrosion causes, such as stress corrosion and thermal cracking, did not serve a role as critical factors regarding to pipeline degradation during 26-years working operation. Actually, the header pipe diameter 32 inches and 40 inches require priority for inspection due to higher corrosion rate compared to smaller pipe diameters. By simulation method on similar heavy duty service condition in which the working pressure of 15 bars and temperature of 183 ℃, it was proved that corrosion rate will severely occur at corrosion rate more than 10 mpy in the pipe diameters of 20 inches, 32 inches and 40 inches. Further,condensation factor may contribute more significant in the case of corrosion under insulation. Practically, the metal loss at a half initial thickness requires priority for inspection, intensive maintenance or possible partial replacement.
基金supported by National S&T Support Program (2006BAB16B01)
文摘In-situ tests and numerical manipulations were conducted for comparison of superior/inferior quality of casing-tube-vacuumized insulation and polyurethane insulation of fi＇eezing apparatuses in relation to non-uniform cold distribution in the multi-coil fi＇eez- ing layout and the contradiction between large-coil diameter layout of the freezing holes and stability of the headfi＇ame base. Tests show that： （1） under current technology, vacuumized insulation is of short duration due to lack of appropriate applied vacuum; （2） after the freezing pipe is insulated with polyurethane, the temperature gradient is less than no insulation, and the temperature dif- ference between insulated and non-insulated apparatuses is stable as the freezing period increases. Finally, it is pointed out that polyurethane insulation is quite efficient in present technical freezing construction. Keywords： freezing pipe; insulation effect; polyurethane; energy conservation
