Stainless steel sewage pump corrosion types

Stress corrosion cracking (SCC): refers to the stress of the alloy in corrosive environment due to the expansion of the crack and the mutual failure of a generic term. Stress corrosion cracking has a brittle fracture morphology, but it can also occur in high toughness materials. Stress corrosion cracking is a necessary condition for the existence of tensile stress tensile stress (whether residual tensile stress or external stress, or both) and the existence of specific corrosive media. The formation and expansion of the pattern is approximately perpendicular to the tensile stress direction. This stress-corrosion cracking stress is much less than the stress required to break the material in the absence of a corrosive medium. At the microscopic point, the crack propagating through the grain is called the transgranular crack, and the crack propagating along the grain boundary is called the intergranular crack. When the stress corrosion cracking spreads to one depth (here, the material on the load-bearing section The stress reaches its fracture stress in the air), the material breaks in the normal crack (in the ductile material, usually by polymerization of microscopic defects). Therefore, the failure of the parts due to stress corrosion cracking will include the stress corrosion cracking of the characteristics of the region and has been associated with micro-defect polymerization, "dimple" area.
Pitting Corrosion: A form of localized corrosion that causes corrosion.
Intergranular corrosion: Grain boundaries are crystallographic orientation of different grains of the disorder between the inter-city, therefore, they are various elements of steel segregation or metal compounds (such as carbide and δ phase) precipitated favorable District City. Therefore, in some corrosive media, the grain boundary may be the first to be corrosion is not surprising. This type of corrosion is known as intergranular corrosion, and most metals and alloys may exhibit intergranular corrosion in a particular corrosive medium.
Corrosion fatigue: in the corrosive medium and the combined effect of cyclic stress generated. This corrosion resistance due to corrosive media caused by the reduction of fatigue performance, known as corrosion fatigue. Fatigue failure stress value is lower than the yield point, in a certain critical cyclic stress value (fatigue limit or fatigue life), the fatigue failure occurs. Corrosion fatigue, however, can break at very low stress conditions, so it is dangerous.
Crevice Corrosion: A form of localized corrosion that can occur either in the stagnant gap of the solution or in the shielded surface. Such gaps may be formed at the junction of metal and metal or metal and non-metal, for example, where rivets, bolts, gaskets, valve seats, loose surface deposits, and marine organisms are present.
Uniform corrosion: refers to the environment in contact with the entire metal surface at almost the same rate of corrosion. In the application of corrosion resistant materials, anti-uniform corrosion should be the main basis for corrosion resistance, in special circumstances (such as cavitation) to consider some of the performance of local corrosion resistance.
Wear corrosion: wear and corrosion combined by the role of the material damage caused by the process of wear and tear corrosion. Wear corrosion can occur in high-speed flow of fluid piping and suspended friction particles containing fluid pumps, pipes, etc.. Some flow components, such as high-pressure valve in the valve (head) and the valve seat, corrosion of these parts in the relative velocity of the medium is very high, so that passivation corrosion-resistant metal surface of the passive film, Excessive mechanical erosion and not easy to restore, corrosion rate will be significantly increased, if there is solid particles in the corrosive medium, will greatly exacerbate wear and corrosion.
Hydrogen embrittlement: metal materials, especially titanium, once hydrogen absorption, it will precipitate brittle hydride, so that mechanical strength degradation. In the corrosive medium, metal precipitation due to corrosion reaction of hydrogen and hydrogen absorption in the manufacturing process, is the main source of hydrogen in the metal. The surface state of the metal has a significant impact on hydrogen absorption, titanium material after oxidation can effectively prevent hydrogen absorption.
V Comprehensive corrosion: is used to describe the surface of the alloy in a more spoon on the way the phenomenon occurred in the erosion of the term. When the overall corrosion occurs, the village expected to gradually thinning due to corrosion, and even corrosion of materials failure. Stainless steel in the strong acid and alkali may show full corrosion. Failure caused by total corrosion is not a cause for concern, since the corrosion can be predicted by simple immersion tests or by reviewing the corrosive literature.
Only by understanding the type of corrosion, in accordance with the principles and characteristics of various corrosion selection of the most suitable stainless steel manufacturing the highest quality stainless steel sewage pump.