The Selection Of Stainless Steel In Corrosive Environment

When choosing stainless steel in a corrosive environment, in addition to having a detailed understanding of the specific use conditions of stainless steel, the main factors that need to be considered are: corrosion resistance, strength, toughness and physical properties of stainless steel, processing, formability, resources, and price And how easy it is to get. Let's introduce them one by one below.

Corrosion resistance

Corrosion resistance includes rust resistance and resistance to acid, alkali, salt and other corrosive media, as well as resistance to oxidation, vulcanization, chlorination, fluorination, etc. at high temperatures. Since the selection of different stainless steels is mainly to solve the problems encountered in actual engineering There are various corrosion problems. For this reason, 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 the corrosion resistance refers to the resistance of stainless steel to the medium. The ability of corrosion damage, so 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 determined artificially. 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 use 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, etc.) Purity) and other requirements. Generally speaking, for equipment, meters and components 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 grades 2 to 5. For equipment with low requirements for easy maintenance or not requiring a long life, components can be selected from grades 4 to 7. Except for special exceptions, stainless steel with an annual corrosion rate of more than 1mm under the conditions of use is 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 the stainless steel is not rusty. Corrosion resistance refers to the relative rust and corrosion resistance. It refers to certain conditions (medium, concentration, (Temperature, impurities, pressure, flow rate, etc.). 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 conditions of use, stainless steel grades After selection, the user department must also use the characteristics of the selected stainless steel correctly, that is, reasonable selection of materials and correct use can achieve the purpose of rust resistance or corrosion resistance.
3. The choice of stainless steel should consider both its general corrosion resistance and local corrosion resistance. In some water and chemical media, the latter needs to be paid more attention. 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. In order to obtain a resistance closer to the actual use conditions 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 will also be encountered. When the working medium or the produced industrial products, even if it contains 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 the 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 stainless steel equipment and components fail due to corrosion, analysis of the cause of corrosion damage should be carried out, and measures should be taken after the cause is found.

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By Minghe Die Casting Manufacturer |Categories: Helpful Articles |Material Tags: Aluminum Casting, Zinc Casting, Magnesium Casting, Titanium Casting, Stainless Steel Casting, Brass Casting,Bronze Casting,Casting Video,Company History,Aluminum Die Casting |Comments Off