For polymers, serving as a protective coating on metals is its old and irreplaceable application. With the expansion of marine-resources exploration, the organic coatings have to serve in deep sea water and to endure the high hydrostatic pressures become a new challenge for organic coating. In this research, we put focuses on the service performance and failure mechanism of the epoxy resin under high hydrostatic pressure (3.5MPa, corresponding to 350m-deep sea water). First of all, we found that degradation processes and failure mechanisms of epoxy resin painted on steels were changed by high pressure resulting in failure before their lifetime. High hydrostatic pressure accelerated the diffusion of water through coatings by altering the diffusion mechanism from ideal Fick diffusion at ordinary pressure to S type adsorption non-ideal Fick diffusion at high pressure. The Electrochemical impendence spectra analysis results showed the barrier and protective properties were deteriorated under the synergic effect of high pressure and water solution. The pull-off test showed that the degradation of bonding between epoxy and steel was much more severely under high hydrostatic pressure due to the acceleration of de-adhesion effect of water on epoxy/steel interface. The failure of coatings was dominated by losing of wet adhesion. The tensile test showed that the strength for epoxy decreased with the increase of immersion time, but to be slower under high pressure than ordinary pressure, and the reason for this phenomenon is probably the "closure effect" caused by high pressure to coating cracks, which decreased the crack propagation under external force. The elongation was increased under high pressure, because of the "plasticization effect" caused by fast water transportation at high hydrostatic pressure. Finally, mathematical models were obtained from three aspects discussed above by theoretical calculation of diffusion equation in water transportation stage, analysis of Grey System Theory on wet adhesion, and linear fitting of coating strength. Then, a comprehensive lifetime prediction model was proposed by introducing the Grey Correlation Analysis method after dimensionless normalization treatment of the previous three mathematical models. Through precision assessment of predicted data by experimental data, the accuracy was found to be excellent, indicating that the suggested model was accurate and had the ability to make precise forecast.
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