As all knows, stainless steel can resist atmospheric oxidation, and also can resist corrosion in the medium containing acid, alkali and salt.
In this way, why stainless steel still rust? 
When the dense protective oxide layer is destroyed it will be easy rust.
Here are the reasons below：
1、When the surface of stainless steel accumulates dust of other metal elements or attachments of dissimilar metal particles, electrochemical corrosion is easy to occur, then resulting in rust.
2、When the surface of stainless steel have organic juice (such as vegetables, phlegm, etc.) attached, organic acid will be formed under the action of water and oxygen, and corrosion will occur after a time.
3、When acid, alkali and salt (such as alkaline water, lime, etc.) are attached to the surface of stainless steel, it is very easy to cause local corrosion.
4、When the air contains sulfide, carbon oxide, etc. (that is, polluted air), it will form sulfuric acid, nitric acid, etc. when it encounters condensed water, which will also cause chemical corrosion.
Suggestions：
1)The surface of decorative stainless steel must be cleaned and scrubbed frequently to remove attachments and eliminate external factors that cause rust.
2) In the seaside area, 316 stainless steel should be used, and the 316 material can resist seawater corrosion.
3) The chemical composition of some stainless steel pipes on the market cannot meet the corresponding national standards and cannot meet the requirements of 304 material, so it will also cause rust.
What kind of stainless steel is not easy to rust？
There are three main factors that affect stainless steel corrosion:
1、The content of alloying elements
Generally speaking, the content of chromium is 10.5%, and the steel is not easy to rust. The higher the content of chromium and nickel, the better the corrosion resistance. For example, the content of nickel in 304 material is 8-10%, and the content of chromium is 18-20%. Such stainless steel will not rust under normal circumstances.
2、The smelting process of the manufacturer will also affect the corrosion resistance of stainless steel.
3、 The external environment, the climate is dry and ventilated, and the environment is not easy to rust.
The air humidity is high, continuous rainy weather, or environmental areas with high pH in the air are prone to rust. 304 stainless steel, if the surrounding environment is too bad, it will rust.
How to deal with rust spots on stainless steel？
1、Chemical ways
Use pickling paste or spray to assist the re-passivation of the rusted part to form a chromium oxide film to restore the corrosion resistance. After pickling, in order to remove all contaminants and acid residues, it is very important to rinse properly with clean water.
After all treatment, re-polish with polishing equipment, and seal with polishing wax. For local slight rust spots, you can also use a 1:1 mixture of gasoline and engine oil to wipe off the rust spots with a clean rag.
2、Mechanical Ways
Sandblast cleaning, blast cleaning with glass or ceramic particles, annihilation, brushing and polishing. It is possible to mechanically wipe away contamination from previously removed material, polishing material, or submerged material. All kinds of contamination, especially foreign iron particles, can be a source of corrosion, especially in humid environments.
Therefore, mechanically cleaned surfaces should preferably be properly cleaned in dry conditions. The use of mechanical methods can only clean the surface, and cannot change the corrosion resistance of the material itself. Therefore, it is recommended to re-polish with polishing equipment after mechanical cleaning and seal with polishing wax.