| Offshore oil and gas pipelines are prone to corrosion problems due to high humidity,high salt and high temperature environments,causing serious economic losses and safety hazards.As an inorganic anti-corrosion coating,low-temperature enamel(LTE)coating has good durability and high temperature resistance,while being able to withstand the intrusion of a variety of chemical media,and is expected to be applied to oil and gas pipeline anti-corrosion projects.However,the melting behavior of LTE coatings during sintering is still unclear.In addition,the anticorrosive coatings applied to the surface of oil and gas pipelines in the marine environment are subjected to a variety of external stresses during use,challenging the mechanical properties of LTE coatings.Based on the above problems,this study aims to explore the melting behavior of LTE coating sintering process,improve the adhesion between LTE coating and steel substrate,develop alumina/enamel composite coating(A-LTE)to improve the abrasion resistance of LTE coating in oil and gas pipeline application environment,and provide a feasible method to extend the service life of LTE coating in oil and gas pipeline.The details of the study are as follows:(1)The sintering behavior of LTE coatings at high temperatures was investigated by simultaneous thermal analyzer,thermomechanical analyzer and selfmade hot stage microscopy.The results show that no chemical reaction occurs during the sintering of LTE coatings,but only a physical melting process,and the viscosity of the coating powder decreases with the increase of temperature.In addition,at the same sintering temperature,the viscosity tends to decrease as the heating rate increases.Through the above tests,the sintering process of LTE coating was finally determined to be the best with a heating rate of 20 ℃/min and a sintering temperature of 530-550 ℃.(2)The surface of steel substrates with different roughness is obtained by varying the abrasive particle size during the blasting process.Subsequently,impact resistance,adhesion tests and Taber abrasion resistance tests were used to characterize the differences in mechanical properties of LTE coatings on steel substrate surfaces with different roughness.The results show that the increase of abrasive particle size during sandblasting can significantly improve the surface roughness of the substrate,enhance the interfacial adhesion and the impact resistance of the coating.For LTE coatings,the basic adhesion force due to chemical adhesion can reach about 2.5 MPa,and substrate surface roughening greatly improves the mechanical adhesion between LTE coatings and steel substrates by increasing the contact area between coatings/substrates and creating typical anchoring structure,but the anchoring effect dominates compared to increasing the contact area.(3)The enamel/alumina composite(A-LTE)coating was prepared by introducing nano-alumina to improve the mechanical properties of the enamel coating.The introduction of nano-alumina significantly improves the surface roughness of the enamel coating,while reducing the formation of cracks on the coating surface due to cooling shrinkage.With the increase of nano-alumina doping,the A-LTE coating has higher microhardness and the brittle nature of the enamel material itself is improved to a certain extent,thus improving the impact resistance of the coating.The lower porosity and higher hardness retarded the expansion of A-LTE coating cracks in the abrasion resistance test,thus reducing mass loss and thickness loss in the abrasion resistance test.The electrochemical test results showed that all A-LTE coatings exhibited good corrosion resistance after 8000 cycles.Among them,the abrasion resistance of A-LTE coatings increased with increasing alumina doping at the same number of abrasion cycle revolutions due to low porosity and reduction of surface cracks. |
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