Abstract
To detect the corrosion resistance of a friction stud welding (FSW) joint in simulated seawater (a 3.5 wt% NaCl solution), the pulse electrochemical deposition method was used for electroplating Ni coating with different duty ratios (50%, 80%, and 100%) on the surface of FSW joint. The microstructure and surface structure of the coating were observed by micro-spectroscopy and other characterization methods. The corrosion behavior of the coating was analyzed by means of macroscopic electrochemical testing. The local corrosion law of joint surface and coating surface defects were innovatively explored by using micro-zone electrochemical scanning system. The coating characterization results showed that, as the duty ratio continues to increase, the coating surface becomes denser and smoother, and the corrosion products such as Fe2O3, Fe3O4, and FeOOH are generated. The results of macroscopic electrochemical experiment indicated that the coating with 100% duty ratio has the lowest corrosion current density and the maximum polarization resistance. The scanning vibrating electrode technique results showed that the corrosion current density in the defect area is higher than that in the coating area, and the maximum corrosion current density decreases with the increase of duty ratio. The localized electrochemical impedance spectroscopy results indicated that the localized impedance at the welded zone was the largest, and with the increase of the pulse duty ratio, the impedance diffusion in the defect area was decreasing.
Highlights
In recent years, with the development of offshore oil industry, the importance of underwater welding technology of steel structure in the submarine pipeline is becoming more and more prominent (Shen et al, 2019)
The results showed that the hardness of base metal zone (BMZ) is higher than stud zone (SZ), and the micro-hardness of welded zone (WZ) is the highest and gradually decreases from the center to the edge
With the increase of the distance from SZ to BMZ, the corrosion current density decreases and increases, and the minimum value of WZ is about 60 μA/cm2. It shows that the WZ has better corrosion resistance after welding
Summary
With the development of offshore oil industry, the importance of underwater welding technology of steel structure in the submarine pipeline is becoming more and more prominent (Shen et al, 2019). It shows that the WZ has better corrosion resistance after welding In this part of the test, the scanning area range of the sample is consistent with that of SVET, and the Z-axis represents the impedance value. The micro area electrochemical test shows that the impedance value of the coating area is significantly higher than the scratch defect area, and the corrosion current density is lower than the scratch area
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