Study On Degradation Of Organic Coatings With Local Mechanical Damage Under Cathodic Protection Through Wire Beam Electrode Technology

This thesis is aim to research the degradation behavior under mechanical damage.This research was completed by using wire beam electrode technique(WBE) and electrochemical impedance spectroscopy technology(EIS).This paper mainly studies the coated carbon steel wire beam electrode samples with epoxy iron red shop primer.First the local degradation and base metal corrosion behavior is studied under the local damage of coating surface. Then a comparative study has performed for the research of the localized degradation behavior of the damaged coating under different cathodic protection potential. Through the analysis of the experimental results, the conclusions are as follows:1. In the case of local damaged coating on the surface, the degradation of the coating will start from the damaged area quickly. Because of the existence of local damage, the failure of the coating will be extended from the point of damage to adjacent area, which is realized by transportation of the electrolyte solution through the metal/coating interface. With the extended of corrosion,the polarity conversion of carbon steel wires can be observed, and in the local corrosion area, there will be a main anode area and a main cathodic region.2. Under the condition of the partial damage of the coating, the effect of different cathodic protection potential on the coating degradation was studied. It can be found in the case of-1.0V cathodic protection potential was applied, during the experimental time period the no damaged region coating performance maintain a good performance, and there is no corrosion current; however in the case of-1.3V of cathodic protection potential is applied, the coating was damaged after soaking in a short time, and the coating appeared obvious peeling phenomenon. Similarly, in the development of corrosion, the main anode area and a main cathodic region in the corrosion area are constantly converted.3.WBE as an means to study the local corrosion, can be used for local degradation mechanism research of coating, and can also be used to study compatibility between different electrode and the organic coating system and the cathodic protection potential.