Research On The Destruction Caused By Stress Corrosion To The Galvanized Steel Coating Of Electric Power Tower

Galvanized steel has low cost and high corrosion resistance mainly used for electric power pylon. In the process of service, some parts of the electric power pylon may stay in a state of stress concentration affected by wire waving and wind vibration, which is combined with atmospheric environment to increase the corrosion of the galvanized layer. Damages caused by stress corrosion have good concealment and severe destruction, which usually lead to catastrophic accidents without any sign, endanger the safety of people and equipment, at the same time bring great losses to production and economy.In this paper, we carry out the laboratory accelerated test and atmospheric exposure test, combined with scanning electron microscopy,electrochemical detection, and X-ray diffraction experimental methods. Studied the affection of stress on the corrosion rate, analysis the corrosion process. Based on these work,we investigated the corrosion types and corrosion rule.The researcher conducts neutral salt spray test and immersion test to samples without stress and with tensile stress, and then uses scanning electron microscope to observe the sections of samples with different stress, at same time measured by impedance spectroscopy and polarization curves. The results indicate pitting corrosion occurs under both conditions. At initial stage, the coating is complete, the corrosion potentials and the current density of samples have no obvious difference, tensile stress is not obvious to corrosion. With corrosion prolong, the current density of samples with tensile stress is 2 to 3 magnitudes higher than that without stress and the impedance module is obviously smaller.A lot of cracks occur in the Zn-Fe coating of the tensile stress samples, which provide good corrosion channels for Cl-, and increase the galvanic corrosion. The existence of tensile stress apparently strengthens the dissolution rate of the zinc coating. Restricted to the oxygen reduction reaction in cathode, immersion corrosion is at a lighter level than salt spray corrosion.The analysis of the X-ray detection indicates the corrosion products are basically same under different stress conditions, mainly including ZnO-. Zn(OH)2、 Zns(OH)8Cl2-H2O、ZnCO3、Zn5(OH)6(CO3)2. According to the stability of corrosion products, we put forward their forming processFrom the kinetic curves and electrochemical laws we find out the corrosion degree of tensile stress specimens are more serious than none and pressure stress specimens.The degree of atmospheric exposure test varies in different areas.The main factors are sulfide, subsidence, air humidity and Cl-.Thesis based on pits growth model and microscopic damage mechanics establish a zinc coating stress corrosion life prediction model. The damage caused by pits equivalent to porosity in materials, through the changes of porosity to predict the lifetime of the coating.