Five points to consider when choosing stainless steel
1. The standard of corrosion resistance is artificially determined. It is necessary to recognize it, use it, and not be bound by it. It is necessary to determine the specific standard of corrosion resistance according to the specific use requirements.
At present, the corrosion resistance of stainless steel mostly adopts the 10-level standard. Which level is selected as the corrosion resistance requirement should consider the characteristics of equipment and parts (thickness, size). The length of service life, product quality (such as impurities, color, Generally speaking, for the equipment, meters and components that require a smooth mirror surface or precise dimensions during use, the 1-3 standard can be selected; The components are selected from grades 2 to 5. For equipment that does not require high requirements for easy maintenance or long service life, the components can be selected from grades 4 to 7. Except for special exceptions, stainless steels whose annual corrosion rate exceeds 1mm are generally not selected. , It should be pointed out that the 10-level standard is not applicable when localized corrosion occurs.
2. Corrosion resistance is relative and conditional. It is often said that stainless steel is rust-resistant. Corrosion resistance refers to relative to rusting and non-corrosion resistance, it refers to certain conditions (medium, concentration, temperature, impurities, pressure, flow rate, etc. for a certain period of time). Up to now, there is no stainless steel with rust resistance and corrosion resistance in any corrosive environment, so the material selection personnel must choose according to the specific use conditions, stainless steel grades After the selection, the user department should also use it correctly according to the characteristics of the selected stainless steel, that is, reasonable selection of materials and correct use can achieve the purpose of being rust-resistant or corrosion-resistant.
3. The selection of stainless steel should consider not only its general corrosion resistance, but also its local corrosion resistance. In some aqueous media and chemical media, the latter needs to be paid more attention. This is because the selection personnel generally pay more attention to stainless steel The general corrosion resistance of stainless steel, and under the conditions of use, their sensitivity to local corrosion, such as stress corrosion pitting corrosion, is less considered; the local corrosion of stainless steel mostly occurs in a corrosive environment with good general corrosion resistance. , Local corrosion often leads to the sudden destruction of stainless steel equipment and components, which is far more harmful than general corrosion.
4. When applying the corrosion resistance data of stainless steel in various manuals, it should be noted that many of the data are only the test results in some experiments, and there are often large discrepancies with the actual medium environment. Corrosion data, in general, the corrosion test of the actual medium or the coupon test under field conditions should be carried out in the laboratory, and the test of the simulation device should be carried out if necessary.
Under some conditions of use, this situation will also be encountered. When the working medium or the industrial products produced, even if there is a trace amount of certain or certain metal ions in the stainless steel, it will affect the chemical process and industrial industry. The quality of the product (including gloss, color, purity, etc.). This situation is most common in industries such as nuclear fuel, pharmaceuticals and pigments. At this time, stainless steel that does not contain a certain element is often selected or the corrosion resistance grade of the selected stainless steel is appropriately improved, so that Reduce metal ions to allowable limits.
5. For stainless steel equipment, if the components fail due to corrosion, the cause of corrosion damage should be analyzed, and measures should be taken after identifying the cause, instead of throwing it away.
