How does chloride corrode stainless steel
In the chloride medium, the stainless steel pipe is often subject to local corrosion is mainly point corrosion and corrosion corrosion two.
Corrosion mechanism of stainless steel
The reason for corrosion resistance of stainless steel pipe is because there is a layer of passivation film on the surface. When this passivation film is destroyed and lacks the conditions or capabilities of the passivation, the stainless steel pipe is corroded. If the corrosion area is concentrated at a specific point and a corrosive pits are developed into the depths, Tube other surface is still passive, this corrosion phenomenon is the point of corrosion.
Stainless steel forms point corrosion conditions
Only in a specific corrosive medium, the stainless steel pipe will form a point of corrosion. When the halogen ions and oxidants (such as dissolved oxygen) are present in the medium, point corrosion is liable to occur. Most of the corrosion of the stainless steel pipe equipment caused by chloride and chloride ions, especially hypochlorite (present in the bleach), the more corrosive. Other halogen ions, bromide will also cause point corrosion, and fluoride and iodide solution, the occurrence of point corrosion of stainless steel tube tend to be smaller. If the chloride solution contains copper, iron and mercury and other metal ions, the corrosion is particularly serious, the risk of corrosion at the point of occurrence of equipment will be greater.
Corrosion characteristics of stainless steel
Stainless steel pipe corrosion occurs when its shape features are the following:
1, most of the stainless steel tube surface almost no corrosion, and some even bright as new, only local corrosive holes.
0Cr18Ni9Ti stainless steel in 10% FeCl3.6H2O solution, room temperature soaking 2.5h after the appearance of the point of corrosion
(A) the original appearance (dents) after soaking (b) (a) After the dents are broken on the top of the wheel, the surface of the wheel of the air compressor made of 1Cr13 martensitic stainless steel The appearance
2, stainless steel pipe looks like no pitting and like to hit the dents, and the dents are metallic luster, but if the broken dents, the following is a serious pitting pits.
The pitting appearance of duplex stainless steel in 10% FeCl3.6H2O aqueous solution at room temperature for 47h
3, the point of corrosion is not only small size, but also by the corrosion products covered, similar to pollutants. After wiping the contaminants, the pits will be exposed.
1Cr18Ni9Ti stainless steel made of pyrithione autoclave liner in the use of pitting pits
4, sometimes stainless steel pipe and part of the environment after the combination of reaction, the point of corrosion will be pagoda-like morphology.
1Cr18Ni12Mo2Ti stainless steel in 10% FeCl3.6H2O solution, 50 ℃, soak for 48h after the appearance of the surface morphology of corrosion.
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