Study On Monitoring Method Of Life-cycle Corrosion Protection For Ship Ballast Tank

Cathodic protection is usually applied to ship ballast tanks on the basis of anticorrosive coatings to improve the effect of corrosion protection.For safety reasons,the cathodic protection system with sacrificial anode is more suitable for ballast tanks.Because ballast tanks are often in harsh environmental conditions,the working characteristics of alternating wetting and drying and the shielding effect of complex structures put forward higher requirements for their cathodic protection system.The sacrificial anode consumption in ballast tank is too fast in the later period of service,and the phenomenon of insufficient local protection often occurs,which leads to potential safety hazards.Therefore,it is particularly important to monitor the corrosion protection status of ballast tank during its life cycle.In this paper,a sacrificial anode cathodic protection system for ballast tank is designed to study the change of corrosion protection status of ballast tank during its life cycle.A method for evaluating the consumption status and service life of sacrificial anode by on-line monitoring is proposed;the protection effect of the whole life is predicted by numerical simulation software;the real sea test of ballast tank scaled model is carried out to verify the accuracy of numerical simulation prediction results,the accuracy of the evaluation method of sacrificial anode consumption status,and the anode current and protection in different life stages are studied.Firstly,the current situation and common methods of corrosion monitoring are introduced.In this paper,a method of evaluating sacrificial anode consumption based on current monitoring data is introduced.The quality of sacrificial anode consumption is calculated by Faraday's law,and the residual life of sacrificial anode is evaluated by average consumption rate.The method of protective potential monitoring based on Evaluation of coating breakage rate is introduced,and the current immersion breakage rate of coating is calculated by measuring low frequency impedance value of coating.The protective potential of the structure is evaluated with the damage rate.Secondly,taking ballast tank as the research object,combined with DnV code and numerical simulation results,the installation location and quantity of sacrificial anode were determined,and the optimized sacrificial anode layout results were obtained.According to the layout scheme,a large-scale model of real sea test was designed,and the preparation of each part of the real sea test was carried out in detail,including: scaled model design and processing construction,surface coating system design and inspection,sacrificial anode insulation installation design,potential measurement device structure design,coating test hanging piece and auxiliary equipment.Finally,the real sea test of ballast tank scaled model is carried out.Artificial damage and immersion accelerated the aging of the coating,and simulated its corrosion protection status in the whole life cycle.The cathodic protection potential and sacrificial anode current of the structure are monitored,and the variation law of the cathodic protection potential and sacrificial anode current in the whole life cycle is explored.