Why stainless steel water tank is also rusty

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When the surface of the stainless steel pipe appears brown rust (point) when people were surprised: that "stainless steel is not rusty, rust is not stainless steel, and steel may be a problem." In fact, this is a lack of understanding of stainless steel a one-sided error view. Stainless steel under certain conditions will be rusty.
Stainless steel has the ability to resist atmospheric oxidation - that is, stainless steel, but also in acid, alkali, salt medium is the ability to corrosion - that is, corrosion resistance. But its corrosion resistance is the size of its steel with its chemical composition, coupled with the state, the use of conditions and environmental media type and change. Such as 304 steel pipe, in a clean and clean atmosphere, there is absolutely excellent resistance to corrosion, but it moved to the beach area, in a large amount of salt in the sea fog, will soon rust; and 316 steel performance good. Therefore, not any kind of stainless steel, in any environment can be resistant to corrosion, no rust.
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Surface film is damaged in many forms, more common in daily life are the following:
      Stainless steel is formed by its surface layer of thin and strong and stable and stable chromium oxide film (protective film), to prevent the continued infiltration of oxygen atoms, continue to oxidize, and get the ability to resist corrosion. Once for some reason, the film has been constantly destroyed, the air or liquid oxygen atoms will continue to infiltrate or metal iron atoms continue to precipitate out to form loose iron oxide, metal surface will continue to rust. This surface film is damaged in many forms, more common in daily life are the following:
1. The surface of stainless steel deposits with other metal elements of dust or heterogeneous metal particles attached to the wet air, the mixture of stainless steel and the condensed water, the two together into a micro-battery, triggering the electrochemical reaction , The protective film is damaged, called electrochemical corrosion.
2. Stainless steel surface adhesion of organic juice (such as melons, soup, sputum, etc.), in the case of water and oxygen, constitute organic acids, long time the organic acid corrosion of metal surface.
3. Stainless steel surface adhesion contains acid, alkali, salt substances (such as decorative walls of alkaline water, lime water splash), causing local corrosion.
4. In contaminated air (such as containing a large amount of sulfide, carbon oxides, nitrogen oxide atmosphere), in case of condensate, the formation of sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.
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To ensure that the metal surface is permanently bright and not corroded, we recommend:
     The above can cause damage to the surface of the stainless steel protective film caused by corrosion. So, to ensure that the metal surface is permanently bright and not corroded, we recommend:
1. Always clean the surface of the decorative stainless steel scrub, remove the attached material, to eliminate the external factors that lead to modification.
2. The beach area to use 316 stainless steel, 316 material can resist seawater corrosion.
3. Some of the chemical composition of the stainless steel pipe on the market can not meet the corresponding national standards, up to 304 material requirements. So it will cause rust, which requires users to seriously choose a reputable manufacturers of products.
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Why does stainless steel bring magnetic
People often think that the magnet adsorption of stainless steel, to verify its advantages and disadvantages and authenticity, do not smoke non-magnetic, that is good, genuine; suction magnetic, is considered counterfeit fake. In fact, this is a very one-sided, unrealistic way to identify the wrong.
A wide range of stainless steel, according to the organizational structure at room temperature can be divided into several categories:
1. Austenitic type: such as 201,202,301,304,316 and so on;
2. Martensite or ferrite type: such as 430,420,410;
       Austenitic type is non-magnetic or weak magnetic, martensite or ferrite is magnetic.
Most of the stainless steel, which is usually used as a decorative tube sheet, is mostly austenitic 304 material. Generally speaking, it is magnetic or weak, but magnetic properties may occur due to chemical composition fluctuation or processing status, but this can not be considered Fake or unqualified, what is the reason for this?
The above mentioned austenite is non-magnetic or weak magnetic, and martensite or ferrite is magnetic, due to smelting component segregation or improper heat treatment, will cause austenitic 304 stainless steel in a small amount of martensite or iron Body tissue. In this way, 304 stainless steel will be with a weak magnetic.
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In addition, 304 stainless steel after cold processing, the structure will be transformed into martensite, cold forming the greater the degree of deformation, the greater the transformation of martensite, steel, the greater the magnetic. Like a batch of steel, production Φ76 tube, no obvious magnetic induction, production Φ9.5 tube. Due to Ling bending deformation of the larger magnetic sense is obvious, the production of rectangular tube deformation due to large diameter, especially the corner part of the deformation is more intense magnetic more obvious.
In order to completely eliminate the above-mentioned causes of the 304 steel magnetic, can be recovered by high temperature solution to stabilize the austenite structure, thereby eliminating the magnetic.
In particular, it is due to the above reasons caused by the 304 stainless steel magnetic, with other materials of stainless steel, such as 430, carbon steel is not the same level of magnetic, that is, 304 steel magnetic always shows the weak magnetic.
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       This tells us that if the stainless steel with weak magnetic or completely without magnetic, should be judged as 304 or 316 material; if the magnetic properties of carbon steel, showing strong magnetic, because the judge is not 304 material.
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