How to use Stainless Steel in a Corrosive Environment
Stainless steel is not easy to rust due to the addition of more than 12% of chromium in the production process, but it is not easy to rust. The environment has a greater impact on the service life of stainless steel, and the corrosive environment can easily cause stainless steel to grow. rust.
So, in addition to a detailed understanding of the specific conditions of the use of stainless steel, what factors should be considered when using stainless steel in a corrosive environment?
Corrosion resistance includes rust resistance and resistance to acid, alkali, salt, and other corrosive media, as well as resistance to oxidation, vulcanization, chlorination, and fluorination at high temperatures.
Since the selection of different stainless steels is mainly to solve various corrosion problems encountered in actual engineering, the corrosion resistance of stainless steel in a corrosive environment is the first consideration for the material selection personnel. Corrosion is the damage caused by chemical or electrochemical action between the metal and the medium, and corrosion resistance refers to the ability of stainless steel to resist the corrosion damage of the medium. Therefore, when corrosion resistance is involved in the selection of materials, the following points need to be paid attention to.
1. The standard of corrosion resistance is artificially determined. It is necessary to recognize it, use it, and not be restricted by it. The specific standard of corrosion resistance must be determined according to the specific user requirements.
At present, the corrosion resistance of stainless steel mostly adopts the 10-level standard. Which level to choose as the corrosion resistance requirement should consider the characteristics of the equipment and each part (thickness, size), the length of the service life, and the quality of the product (such as impurities, color, Purity), and other requirements. Generally speaking, for equipment, meters, and parts that require smooth mirrors or precise dimensions during use, you can choose 1 to 3 standards; for equipment that requires close cooperation, long-term leakage, or limited use of equipment, The components are selected from 2 to 5 grades.
For equipment that does not require high maintenance convenience or requires a short service life, the components can be selected from 4 to 7 grades. Except for special exceptions, stainless steels with an annual corrosion rate of more than 1 mm under the conditions of use are generally not used. It needs to be pointed out that the level 10 standard is not applicable when local corrosion occurs.
2. Corrosion resistance is relative and conditional. It is often said that stainless steel is not rusty. Corrosion resistance refers to the relative rust and corrosion resistance. It refers to the Temperature, impurities, pressure, flow rate, etc. for a certain time). Up to now, there is no stainless steel that is rust-proof and corrosion-resistant in any corrosive environment. Therefore, the optional material personnel must choose according to the specific use conditions. Stainless steel grades After selection, the user department must also use the characteristics of the selected stainless steel correctly, that is, rational selection of materials and correct use can achieve the purpose of rust resistance or corrosion resistance.
3. The choice of stainless steel must consider its general corrosion resistance and local corrosion resistance. In some water and chemical media, the latter needs to be paid more attention to. This is because the material 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, etc., 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 test results in some experiments, and there are often large discrepancies with the actual medium environment. Corrosion data, in general, the actual medium corrosion test or the coupon test under field conditions should be carried out in the laboratory, and the simulation device test should be carried out if necessary.
Under some conditions of use, this situation may also be encountered. When the working medium or the produced industrial products, even if there is a trace of a certain or certain metal ion in the stainless steel, it will affect the chemical process industry. The quality of the product (including gloss, color, purity, etc.). This situation is most common in nuclear fuel pharmaceutical and pigment industries. At this time, stainless steel that does not contain a certain element is often used or the corrosion resistance grade of the selected stainless steel is appropriately increased in order to Reduce the metal ions to the allowable limit.
5. If the components of stainless steel equipment fail due to corrosion, the cause of corrosion damage should be analyzed, and measures should be taken after the cause is found.
Therefore, in actual use, great attention should be paid to the actual use environment of stainless steel. By selecting the appropriate stainless steel, the occurrence of corrosion can be reduced and the service life of stainless steel should be prolonged.