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AgCuZnSn filler metals were prepared from the BAg34CuZnSn filler metal by a combinative process of brush plating and thermal diffusion, and the prepared filler metals were applied to the induction brazing of the 316LN stainless steel. The corrosion behaviors of the brazed joints was evaluated based on local corrosion analyses, where the morphology of the joints was analyzed by scanning electron microscopy (SEM) after immersion in a 3.5 wt.% NaCl aqueous solution and electrolytic etching in a 10 vol.% oxalic acid solution. The microstructure of the brazed joints with the Sn-plated filler mainly consisted of the Ag phase, Cu phase, CuZn phase, Cu₅Zn₈ phase, Cu${}_{41}$Sn${}_{11}$ phase and Ag₃Sn phase. The local corrosion analysis results indicated that galvanic corrosion occurred near the interface between the stainless steel base metal and the brazing seam. With increasing local corrosion time, the corrosion rates of both the brazing seam and the base metal first exhibited an increasing trend, followed by a decreasing trend, and the corrosion rate of the brazing seam was slightly greater than that of the base metal. The corrosion behaviors analysis indicated that the corrosion resistance of the brazing seam was reduced, and concave defects emerged after electrolytic etching for 90 s.

In this paper, the electrochemical performance of a novel gradient-distributed wire beam electrode (WBE) is measured in different corrosion medium. This electrode contains three kinds of carbon steel with different carbon content. WBE was consisted of 100 carbon steel wires and regularly prepared into a $10\times 10$ matrix. The carbon steel wires for each row is the same, but the adjacent rows are different. The electrochemical corrosion behavior of regions with different carbon steel wires can be tested clearly. The results revealed that the heterogeneity of local corrosion of metal, which can be well studied by WBE, meanwhile, the phenomenon of polarity reversal can also be detected. Corrosion potential–current distribution map of the novel WBE showed obvious striped features when immersed in 3.5wt.% NaCl solution with different pH (pH$=$2, 6 and 12). Corrosion firstly occurred in the high carbon steel region in the acidic conditions, and then quickly spreads to other areas, eventually causing the entire surface of the WBE to be corroded. While in the neutral salt solution, only the regions of high carbon steel and some part of medium carbon steel area appeared obvious anode currents during a long time testing. When the pH of corrosive solution reached to 12, the corrosion rate is greatly reduced and then corrosion process is suppressed. This new method can evaluate the corrosion resistance of materials more accurately.

The influence of slug flow on local corrosion of pipeline was studied, and the protection measures for slug flow corrosion were well done to improve the safety of oil-gas-water-humidity mixed pipeline. An indoor loop test was designed to simulate the slug flow in real undulating pipelines. The surface microstructures of X70 hanging pieces were studied by scanning electron microscopy (SEM) under slug flow conditions at different test stages. At the beginning of the test, there was much pitting corrosion on the surface of the hanging pieces, but at the end of the test, only some pitting or pitting spots developed into serious local corrosion. The flow corrosion of slug in pipe had obvious characteristics of cavitation corrosion. Its occurrence was the result of synergistic action of various mechanisms. The strong impact force, high impact velocity and mechanical action of multi-frequency micro-jet produced by cavitation annihilation significantly affected the development process and characteristics of electrochemical corrosion, which resulted in that the cavitation corrosion was mostly pitting corrosion. The damage of corrosion product film caused by high-speed micro-jet impact caused by cavitation cracking was local, and the pitting tendency increased at the local damage of corrosion product film. However, with the formation of electrochemical corrosion products, the destroyed corrosion product film was repaired continuously, but did not develop into local corrosion. Local corrosion occurred only when the high-speed micro-jet with cavitation breakdown repeatedly impacted a point of pitting tendency, but this probability was smaller than that of pitting tendency.