What factors need to be considered when choosing stainless steel

Because corrosion is the damage caused by chemical or electrochemical reactions between metal and the medium, and corrosion resistance refers to the ability of stainless steel to resist the corrosion damage of the medium, when considering material selection, attention should be paid to the following points when it comes to corrosion resistance:

1. Firstly, the standards for corrosion resistance are determined by humans, and they should be acknowledged and used. However, they should not be blindly adhered to. Specific standards for corrosion resistance should be determined based on specific usage requirements.

Nowadays, the corrosion resistance of stainless steel is usually measured by the 10-level standard. When choosing which level to use as the corrosion resistance requirement, the specific conditions of the equipment should be considered. The service life of the stainless steel inside, product quality requirements, etc. Generally speaking, for equipment and components that require smooth surfaces or precise dimensions during the process, it is best to choose the 1-3 level standard. For equipment and components that require close cooperation, long-term no leakage or a limited service life, the 2-5 level standard is suitable. For equipment with low requirements for maintenance convenience or short service life, it is best to choose the 4-7 level standard. Except for special exceptions, stainless steel is rarely selected when the corrosion rate under the usage conditions exceeds 1 millimeter. It should be pointed out that the 10-level standard is not applicable when there is local corrosion.

2. Secondly, corrosion resistance is relative and conditional. The so-called corrosion resistance of stainless steel refers to the corrosion resistance performance relative to rusting and non-corrosion resistance. It refers to under certain conditions. Up to now, there is no stainless steel that does not rust in any corrosive environment. Therefore, when selecting materials, specific conditions of the equipment should be considered. After selecting the stainless steel grade, the using department should also correctly use the selected stainless steel based on its characteristics. That is, to achieve the purpose of having corrosion resistance or corrosion resistance, reasonable material selection and correct use are necessary.

3. In addition, when choosing stainless steel, not only the performance that can resist common corrosion should be considered, but also the ability to resist local corrosion. In some water media and chemical media. The latter requires particular attention. This is because the material selection personnel usually pay more attention to the general corrosion resistance performance of stainless steel, but in general usage conditions, their sensitivity to local corrosion, such as stress corrosion pitting corrosion, etc., is considered less. Local corrosion of stainless steel often occurs in corrosion environments with good general corrosion resistance performance, and local corrosion often leads to the sudden failure of stainless steel equipment and components. This hazard is much higher than general corrosion.

In some usage conditions, there may be a certain situation where, even if there are trace amounts of certain metal ions in the working medium or the produced products, it still affects the quality of the chemical process and industrial products (including luster, color, purity, etc.). This is most common in nuclear fuel, pharmaceuticals and pigments. Here, stainless steel without certain elements is usually selected, or when the corrosion resistance grade of the selected stainless steel is improved, the metal ions can be reduced to an allowable limit.