In seawater pipeline, the welding joint is a non-uniform structure composed of welding seam, base metal and heat affected zone. It has inhomogeneity in chemical composition, organizational structure, residual stress, etc. As local defects and high turbulence accelerate corrosion, the welding joint is often the weakest link in pipeline corrosion. Herein, the electrochemical corrosion behavior of B10 alloy welded joint in flowing seawater is studied from macroscopic and submicroscopic viewpoints using AC impedance, linear polarization, array electrode and morphological characterization. The results reveal that the corrosion rate of weld metal (WM), base metal (BM) and heat-affected zone (HAZ) decreased with the increase of time. Combined with SEM and EDS analysis, it can be seen that the increase in time led to the decomposition and accumulation of corrosion products, which gradually enhanced the corrosion resistance of welded joints. At the submicroscopic scale, WM acts as a cathode to mitigate corrosion during the later stages of high flow rate.

Titanium alloy has been widely used in Marine pipeline system because of its excellent corrosion resistance. However, there are differences in microstructure and electrochemical properties because of the heterogeneous structure of the welded joint, the corrosion behavior is often different. In this paper, the corrosion behavior of TA2 titanium alloy welded joint in seawater at different temperatures was studied by traditional macro electrochemical test analysis combined with microelectrode array test and surface morphology analysis. Conventional macroscopic electrochemical analysis results show that the corrosion resistance of heat-affected zone is always the best, followed by the base metal and the weld. And the higher the temperature, the easier the formation of passivation film. The results of microelectrode array test show that the heat-affected zone is always the cathode region of the whole welded joint, and part of the cathode near the base metal region has the largest current density, which acts as the main cathode to slow down corrosion. At slightly higher temperatures, the polarity deflection will occur in the base metal zone and weld zone due to the different formation speeds of passivation film in early corrosion stage. With the prolongation of corrosion time, the base metal eventually becomes the cathode zone and the weld zone eventually becomes the anode zone.

Due to its excellent performance, 90-10 cupronickel has been widely used as a pipeline for marine engineering. However, due to the harsh service conditions of flowing seawater, the problem of corrosion leakage is extremely serious. One of the most common locations is the welding joint. In this paper, electrochemical impedance spectroscopy, surface morphology analysis techniques (scanning electron spectroscopy, energy disperse spectroscopy, three-dimensional microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy) are used to study the corrosion resistance of 90-10 cupronickel (MZ), heat affected zone (HAZ) and welding zone (WZ). The experimental results show that MZ, HAZ and WZ can form protective corrosion product film in flowing seawater, and that the corrosion resistance increases with the experiment time increasing and achieves the maximum value after 20 days. However, the corrosion resistance of HAZ is smallest due to the low adhesion density of corrosion production formed on HAZ. HAZ is preferentially corroded for minimum corrosion resistance and galvanic corrosion between WZ and HAZ.