The Point Corrosion of Seamless Square Tubes

Alloy Composition: Elements like 0, 10, and F enhance the corrosion resistance of seamless square tubes, while elements like K may decrease it. The effect of alloy elements depends on their presence in solid solution or as intermediate metal phases.

Cold Working: Cold working of austenitic seamless square tubes increases dislocation density, leading to more pits on the surface, albeit smaller in size, thus increasing the tendency for point corrosion.

Surface Condition: The surface finish of the material determines its corrosion potential. Different surface finishes can result in significant differences in corrosion potential within the same material environment.

Oxides: Oxides formed during heating in air can significantly impact the corrosion resistance of the material.

Microstructure: Various phases such as sulfide inclusions, delta ferrite, sensitized grain boundaries, and welds can profoundly affect the corrosion resistance of the steel pipe.

Welding: Oxide films formed during welding may adversely affect the corrosion resistance of the alloy in aggressive chloride solutions.

Passivation Treatment: Passivation treatment can improve the corrosion resistance of seamless square tubes by removing surface inclusions and contaminants. However, it's important to rinse the tubes with a sodium hydroxide solution after passivation treatment.