Study On Selection Of Steel And Cathodic Protection Of Flow Passage Components For Tide Generating Set

As a renewable energy technology with huge development potential,tidal power generation is the most mature and largest-scale developed.Unlike traditional hydro-turbines,tidal turbines operate in seawater mediums with severe corrosion.Corrosion protection has become a key issue that restricts the development and utilization of tidal turbines.For tidal unit flow-through components,seawater flow will change the concentration of dissolved oxygen at the corrosion interface,and water scouring will affect the formation and stability of corrosion products.Traditional electrochemical studies are performed under the condition that the corrosive medium is stationary.The influence of seawater flow on the corrosion mechanism,corrosion rate,and electrochemical protection parameters is unclear.In addition,due to the large number of components in the tidal unit and the complex structure,it is necessary to develop a model device to evaluate the feasibility and effectiveness of the cathodic protection.In view of the above problems,this study prototyped a rotating and dielectric circulating electrochemical electrochemical testing device which achieved the corrosion resistance test of the flow-through component material under simulated conditions(medium flow).Corrosion Polarization Curves,Electrochemical Impedance Spectroscopy and the corrosion microscopic are performed.The results show that with the increase of seawater flow rate,the corrosion mechanism of the material does not change significantly,but the corrosion rate increases significantly.When the seawater flow rate increases from 0m/s to 3m/s,the corrosion current density of carbon steel such as B780 CF and stainless steel such as ZG04Cr13Ni5 Mo increases approximately 100% and 200%.The microscopic morphology of corrosion shows that carbon steel such as B780 CF suffered from uniform surface corrosion.The shedding of corrosion product caused by seawater flow was the main reason for the increase of corrosion rate.The stainless steel such as ZG04Cr13Ni5 Mo suffered pitting corrosion,and corrosion become more serious due to the increase of dissolved oxygen concentration caused by seawater flow make.The protection current density of the material under different seawater flow rates was tested with a stable protection potential.The protection current density increased by 40%~75% when the seawater flow rate increased from 0m/s to 4m/s.When designing the cathodic protection solutions,the increase in protection current caused by seawater flow should be considered.A cathodic protection anti-corrosion model device based on the tubular unit was designed and developed.The finite element analysis method was used to simulate and calculate the fluid flow conditions and the electrostatic field distribution inside the corrosion model device.The device can be used to evaluate and optimize the selection of materials of tidal units.It can also be used to confirm the effectiveness of anti-corrosion structure design and cathodic protection schemes.