Factors affecting corrosion of seamless steel pipe

1. For seamless steel pipes, 0, 10 and F are the main alloying elements which make the have good resistance to pitting corrosion. Other elements may also have some effect, while K and other elements will reduce the pitting corrosion resistance of Q235 Black ERW Welded Seamless Steel Pipe. It is certain that the effect of elements on the corrosion resistance of materials is summarized briefly. The impact of 13 and 0 is changing. 3 is beneficial in solid solution, but harmful when precipitated as intermediate metal phase, 0 is harmless in solid solution and harmful when precipitated with carbide, but slightly harmful.

　　2. The microstructure of seamless steel pipe plays an important role in the resistance to pitting corrosion of alloys. Various phases, such as sulfide inclusions and 3 ferrite. Phases, sensitized grain boundaries and welds may have a decisive impact on the pit corrosion resistance of steel. They are the most sensitive sites for pit corrosion. For the cast seamless steel pipe with complex microstructures and martensitic seamless steel pipe with sensitive microstructures to heat treatment process, the relationship between pitting corrosion and constituent phases is more close. It should be noted that the composite manganese sulfide inclusions are more sensitive to spot corrosion. Therefore, aluminum deoxidizer should be avoided when smelting seamless steel pipe.

　　3. The research on cold-working of austenitic seamless steel pipe shows that the number of pits on the surface of samples increases and the size of pits decreases after cold-working. This is due to the increase of dislocation density in cold processing, dislocation in the surface outcrop is prone to cause pitting corrosion, cold processing has the trend of increasing pitting corrosion.

　　4. For a given alloy environment system, the factor determining the pitting corrosion potential of the alloy is the smoothness of the material surface. In fact, it is meaningless to compare the pitting corrosion tendency of carbon with different surface finish. The effect of surface finish on the spot corrosion properties of seamless steel pipe is shown in the figure. It shows that in the same material environment system, if the surface finish is different, the difference of pitting corrosion potential can be more than 14.

　　The oxide formed by heating in seamless steel pipe in air may have a significant impact on the pitting corrosion resistance. The oxide film produced by welding may be detrimental to the pitting corrosion resistance of the in strong chloride solution.

　　The main function of passivation treatment is to dissolve the inclusions and contaminants on the surface of seamless steel pipe and make them clean. It can also remove the manganese sulfide inclusions on the surface. Such inclusions may become the source of pitting corrosion and thus improve the pitting corrosion resistance of seamless steel pipe. It should be noted that the seamless steel pipe is cleaned by sodium hydroxide solution after passivation.