Erosion Corrosion Performance Of 304 Stainless Steel Welded Joints In Liquid-Solid Two-Phase Flow

Pipe network construction and the energy industry are developing vigorously and orderly.304 austenitic stainless steel is widely used in the petroleum and petrochemical industry due to its good corrosion resistance,weldability and high formability,and is often welded to connect pipelines or equipment.The fluid and the particles it carries during high-speed flow will exert erosion corrosion on the welded joint,which will cause the welded joint to suffer mechanical damage and electrochemical corrosion and synergistic effects,resulting in failure and loss.At present,there are some blanks in the research on the erosion corrosion and critical flow velocity of 304 welded joints in liquidsolid two-phase flow.Therefore,it is necessary to study the erosion corrosion characteristics and critical flow velocity of 304 welded joints,which has reference significance for reducing accident rate,energy waste and corrosion cost.In this paper,X-ray Diffractometer(XRD),electrochemical workstation,metallographic microscope and other instruments are used to characterize the basic characteristics of welded joints,and the flow corrosion characteristics of welded joints in single-phase fluid are studied.The erosion corrosion characteristics and critical flow velocity phenomena of welded joints and substrates in liquid-solid two-phase flow were analyzed by means of erosion corrosion rate,roughness,electrochemical measurement and subregional characterization.The study found microstructure of the welded joints and the base metal samples differ greatly in morphology and grain size.The content of Cr and Ni in the welded joints decreased,and the C content increased significantly,the corrosion resistance of the welded joints was obviously weaker than that of the base samples.The results of single-phase flow corrosion experiments show that the corrosion characteristics of welded joint samples and base metal samples in 0.5% sodium chloride solution show opposite trends with the increase of flow velocity.After the flow velocity increased,the corrosion resistance of the 304 base metal was slightly improved due to the lack of particle action;however,the corrosion of the welded joints continued to deteriorate due to welding reasons and the existence of galvanic corrosion,and the corrosion resistance of the heat-affected zone was better than that of the weld zone.The research results of liquidsolid two-phase flow erosion corrosion show that: the increase of flow velocity leads to the continuous increase of erosion corrosion rate,corrosion current density and roughness value,and there are critical values.The critical flow velocity of the welded joint is lower than the critical flow velocity of the base metal under the same conditions.The change of concentration of sodium chloride solution will not affect the critical flow velocity of the base metal,however,the increase of sodium chloride concentration will reduce the critical flow velocity of erosion corrosion of welded joints.The main reason why the welded joint is different from the base metal is the uneven distribution of elements,microstructure difference,galvanic corrosion and welding defects caused by welding.Welding defects and their development in the process of erosion corrosion are one of the important reasons for the failure of welded joints.Welding defects will increase the roughness of welded joints and affect the electrochemical corrosion activity to promote corrosion;the destruction of the hydrodynamic boundary layer and the diffusion boundary layer leads to the disturbance of wall shear stress and mass transfer,which makes the local area unable to reach a stable state and deteriorates erosion corrosion.