What is the relationship between the corrosion resistance of stainless steel pipes and their materia

The corrosion resistance of stainless steel pipes is closely related to their material, and it is mainly manifested in the following aspects: 

The influence of alloy elements

Chromium (Cr): It is one of the most important alloy elements in stainless steel pipes. Chromium can form a dense chromium oxide film on the surface of the pipe, which acts as a protective layer that prevents oxygen, water, and other corrosive substances from coming into contact with the metal substrate, thereby achieving the effect of corrosion prevention. Generally speaking, the higher the chromium content, the stronger the corrosion resistance of the stainless steel pipe. For example, the chromium content of 304 stainless steel is approximately 18%, while that of 316L stainless steel is between 16% - 18%, both of which have good corrosion resistance. 

Nickel (Ni): It can enhance the corrosion resistance of stainless steel, especially having a significant effect on acid resistance and alkali resistance. Nickel can also increase the toughness and ductility of stainless steel, making it less prone to cracking and corrosion fatigue in various environments. For instance, the nickel content in 304 stainless steel is approximately 8% - 10.5%, while that in 316L stainless steel is in the range of 10% - 14%. This enables them to exhibit excellent corrosion resistance in many industrial settings. 

Molybdenum (Mo): It can enhance the corrosion resistance of stainless steel tubes in reducing media, and improve their ability to resist pitting and crevice corrosion. Its effect is particularly significant in environments with chloride ions. For example, 316L stainless steel contains 2% - 3% molybdenum, making it more resistant to corrosion by seawater and other chloride-containing media than 304 stainless steel without molybdenum. 

The influence of organizational structure

Austenitic stainless steel: Such as 304 and 316L stainless steel, have a face-centered cubic crystal structure. This structure gives them excellent toughness, weldability and corrosion resistance. Austenitic stainless steel has a single-phase austenite structure at room temperature and is not prone to phase transformation, thus maintaining stable corrosion resistance. 

Ferritic stainless steel: Contains a high amount of chromium and has a body-centered cubic crystal structure. It has good corrosion resistance, especially a strong resistance to stress corrosion cracking, but its toughness and weldability are relatively poor. 

Duplex stainless steel: For example, 2205 duplex stainless steel is a type of stainless steel composed of austenite and ferrite phases. This duplex structure enables it to possess the advantages of both austenitic stainless steel and ferritic stainless steel, offering good strength and toughness, as well as excellent corrosion resistance. Particularly, it performs exceptionally well in resisting pitting corrosion, crevice corrosion, and stress corrosion cracking. 

The influence of carbon content: The carbon content has a certain impact on the corrosion resistance of stainless steel pipes. Generally speaking, the lower the carbon content, the better the corrosion resistance of stainless steel. This is because carbon reacts with chromium to form chromium carbide, which reduces the chromium content in the matrix, thereby weakening the formation and integrity of the oxide chromium protective film. For example, the "L" in 316L stainless steel indicates low carbon, with a carbon content of no more than 0.03%. Compared to ordinary 316 stainless steel, it has better intergranular corrosion resistance.