Selection of Stainless Steel and Nickel Alloys By yaang.com

Corrosion resistance of stainless steel or heat-resistant steel is usually the most important features, but in the application, corrosion resistance, the most difficult assessment. Under natural conditions, and in pure chemical solution, the corrosion resistance is relatively easy to determine. However, localized corrosion, such as: stress corrosion cracking, crevice corrosion, pitting corrosion, intergranular corrosion (present in the HAZ) is much more complex than the general corrosion. Although there is no such localized corrosion on the structural damage to a large area, but may not be expected to result from, or even fatal failure.

Therefore, construction and choice of stainless steel in the design must carefully consider these factors. Corrosion may be through the media, alarming increase in minor impurities, the impurities in the media is difficult to predict, but even if it is the concentration of parts per million can cause serious consequences. In the case of warming, although minor changes in the atmosphere will greatly accelerate the corrosion of metals, may affect the corrosion rate, curing and carburization. 

Despite these complexities exist, we can combine the steel manufacturer's recommendations to select the appropriate rule of thumb for most applications of steel. However, to understand one thing: the material obtained by the corrosion test data for predicting performance of a particular kind of deviation from time to time. Even the work the data have been limited because of corrosion similar to some of these media may be due to slight changes in the erosion factors have substantial differences. For demanding applications that require extensive data for these two studies, comparative analysis, and sometimes will follow the lead testing or operation test. 

The mechanical properties of the working temperature is the primary consideration, but sometimes overlook other temperature requirements to achieve a satisfactory performance. Therefore, the products used for low temperature below zero must have for the performance of the work, although a constant operating temperature may be much higher, at room temperature in work performance are also important. 

The choice of products not only need to consider the needs of performance, but also consider the handling of processing andcleaning needs. Can be processed with a particular characteristic (easy to shape or weldability) of the material would normally be used, not the other, but that relatively good performance of the high cost of materials processing. Even the cleaning process will also affect the choice of steel. Sometimes, even if the working conditions in the degree of sensitization is not important, but need to be adopted by the welding process of the stable carbon materials that may be ignored.

The welding process of the material needs to be placed in a washing medium, such as nitric acid - hydrofluoric acid, sensitized by the media will corrode stainless steel or nickel alloy. For some specialized applications, other properties listed in the list is critical. but in many other applications are rarely considered. Surface finish are important for many applications, sometimes using stainless steel, because it has a beautiful surface for a variety of options. According to the appearance, smoothness and other characteristics, or to select the cleaning surface. Surface in terms of cleaning is not as easy as it is sometimes, the existing test surface may be desirable. The choice of surface layer may affect the type of choice, the choice of the surface layer in turn may affect the choice of material grade, because the different levels of surface layer, the durability of the surface layer are also different. Strong level of corrosion resistance in corrosive solution (the lower alloy content will corrode steel) in the surface layer remains bright.

Source: Yaang Pipe Industry Co., Limited (www.yaang.com)