Studies On Inhibiting Washes For Intermittent Immersion Parts Of Ships

So far, inhibitors have been developed more than 100 years and enormous achievements have been obtained including production and research on mechanism of inhibition. At present, the majorities of inhibitors are applied to the system of continued immersion and closed system of vapor phase. However, research reports of inhibitors, used under rinsing technology condition, are even rare. Under harsh marine environment, when the intermittent immersion parts of ships float upward, these parts are only protected by coating. However, it is found that coating appears cracking and spalling behavior because of construction technology and coat aging. As a result, the intermittent immersion parts have become one of the severest corrosion areas. In order to remedy the problems associated with corrosion, using inhibiting washes is a effective and feasible method. Using inhibiting washes not only prolong lifetimes of ships and reduce cost of maintenance, but also enlarge applied field on inhibitors.In this thesis, weight-loss methods were employed for sift of inhibitors, according to feature of rinsing technology. Inhibitors selected had high inhibition efficiency for 907A, 921A, 980 steel which were main materials of ship shells. On the other hand, the corrosion inhibition efficiency was tested for aluminum alloy sacrificial anode, copper, HDR duplex stainless steel, titanium60, which were inner materials of ship superstructure. And rinsing technology was studied. The corrosion inhibition ability and mechanism of commercial inhibitors on 907A steel were discussed with the methods of potentiostatic polarization, electrochemical impedance spectroscopy (EIS), constant potential step, investigation of the microscopic topographies, using environment scanning electron microscopy. The main conclusions were as follows:By using that weight-loss method, ADD4, ADD5 and ADD10 can inhibit corrosion of 907A, 921A and 980 steel, and inhibition efficiency reached at more than 90%. The optimum ratio of complex inhibitors was obtained by orthogonal experiment. The complex inhibitors consisted of four portions of ADD4, four portions of ADD5 and one portion of ADD10. The concentration of complex inhibitors was 2.5ml/L. And the inhibition efficiency of complex inhibitors for 907A, 921A, 980 steel respectively reached at 97.28%, 94.15%, 97.21%. Complex inhibitors had no significant influence on electrochemical properties of aluminum alloy sacrificial anode by electrochemical tests. At the same time, the corrosion rates of copper, HDR duplex stainless steel and titanium 60 were not accelerated after the use of complex inhibitor. And complex inhibitors had a certain protection on copper.According to actual condition, the best rinsing technology was acquired from some feasible technologies. It was that firstly, tap water was employed to remove salinity of surface and secondly, inhibitors was employed to rinse surface of ship.When samples were immersed in the sea water for longer time, complex inhibitors had more effect compared with blank samples. The longer the immersion time was, the higher the inhibition efficiency was. The period of rinse was once every three weeks. Corrosion inhibition mechanism of ADD4, ADD5 and ADD10 had been studied.The inhibiting mechanism on the condition of immersion was investigated Electrochemical Impedance Spectroscopy. Results of polarization curve showed that the inhibitors ADD4, ADD5 and ADD10 were all mix-type inhibitors, which mainly inhibited anode process. In the initial period of rinsing, the liquid film was thick, equivalent to immersion. The constant potential step technique was employed to explain the inhibiting mechanism of initial rinsing period by polarization resistance (Rp) and double-layer capacitance (Cd). The scanning electron microscopy (SEM) and X-ray energy dispersion spectroscopy (EDS) were employed to investigate inhibition behaviors of inhibitor ADD5 on 907A steel.