| 2205 Duplex stainless steel(DSS)is widely used in valves,pipelines and other overflow components because of its excellent resistance to pitting corrosion,SCC resistance,good overall mechanical properties and weldability.In the process of coal chemical production,it is vulnerable to corrosion by the high chlorine environment,and the flow of high chlorine wastewater will cause more serious corrosion damage to duplex stainless steel.In addition,there is a large performance difference between duplex stainless steel with different two-phase ratio,so reasonable control of the two-phase ratio of duplex stainless steel is very important.In this paper,2205DSS is used as the research object to investigate the effects of different flow rates as well as impact angles on the corrosion behavior of the material in high chlorine solution to provide a theoretical basis for coal chemical corrosion protection measures.On the basis of the experimental laws derived,the corrosion resistance of 2205DSS with different two-phase ratios in static as well as flowing environments is studied to find out the best two-phase ratio for corrosion resistance in different environments and to provide guidance for the heat treatment and welding process of duplex stainless steel.The main research contents and results are as follows:(1)A set of jet-type flow corrosion experimental platform with adjustable angle and controllable flow rate was built.And numerical simulation models were established based on the built experimental platform,which provided guidance and complemented the subsequent experiments.(2)The effects of flow rate and impact angle on the corrosion behavior of 2205DSS were investigated by a combination of experiments and simulations.The results show that the corrosion rate of 2205DSS in a 3.5 wt%NaCl solution in the flow state accelerates as the flow rate increases from 0 m/s to 6 m/s,and when the flow rate exceeds 4 m/s,a larger increase in the corrosion rate occurs.The increase of the flow rate will promote the cathodic reaction,so that the self-corrosion potential shifts positively,resulting in an increase in diffusion current density,reducing the ability of the passivation film to protect the metal so that the anode metal dissolves faster and the corrosion rate rises;The corrosion rate of 2205DSS in 3.5wt%NaCl solution in the flowing state increased with the increase of the impact angle.However,compared with the flow rate,the corrosion rate of 2205DSS was less affected by the impact angle.The comparison between simulation and experiment shows that the corrosion behavior of 2205DSS in 3.5 wt%NaCl solution with different impact angles is mainly controlled by the impact pressure applied to the surface.In the single-phase flow,the shear force on the material surface is small and the cutting effect on the metal surface is weak,which is not enough to destroy the passivation film on the material surface.(3)In the static high chlorine environment,the specimen with the ratio of two phases close to 1:1 has the best corrosion resistance.Due to the relatively close content of the two phases,the potential difference is very small,and the galvanic corrosion effect is not obvious,which determines that both tissue states have good pitting resistance,at the same time,the redistribution of Cr,Mo and other elements also has a positive impact on the corrosion resistance of the material;in the flowing high chlorine environment,when the volume fraction of α-phase is 53.82%,2205DSS achieves the lowest corrosion rate,the reason for this phenomenon may be that different Heat treatment of the specimens after the corrosion resistance gap is small,while the hardness increases with the increase in the temperature of solid solution,under the combined influence of hardness and corrosion resistance led to the above phenomenon.In addition,fluid flow has a positive effect on pitting inhibition,but in the flow environment,once pitting is formed,fluid flow will promote the growth and expansion of pitting,thus leading to increased corrosion. |
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