Stainless steel pump corrosion resistance

Stainless steel submersible pumps stainless steel magnetic pump stainless steel chemical pump stainless steel centrifugal pump The corrosion resistance of stainless steel generally increases with the increase of chromium content. The basic principle is that when there is enough chromium in the steel, a very thin and dense oxide film is formed on the steel surface to prevent further oxidation or corrosion. Oxidizing environment can strengthen this film, and the reducing environment will inevitably destroy this film, resulting in corrosion of steel. (1) Corrosion resistance in various environments ① atmospheric corrosion stainless steel atmospheric corrosion is basically the content of chloride in the atmosphere with the change. Therefore, the corrosion of stainless steel near the ocean or other sources of chloride is of paramount importance. A certain amount of rainwater is only important when it comes to the chloride concentration on the steel surface. The 1Cr13, Cr17, and austenitic stainless steels for rural environments are adaptable to a variety of uses without noticeable changes in appearance. Therefore, stainless steel used in rural areas can be selected based on price, market availability, mechanical properties, processability and appearance. Industrial environment 1Cr17 and austenitic stainless steels work long hours in industrial environments that are free of chloride contamination and remain essentially rust-free and may form a fouling film on the surface but when the fouling film is removed, the original Bright appearance. In chloride-containing industrial environments, corrosion of stainless steel will result. Marine environments 1Cr13 and 1 Cr 17 stainless steel form a thin film of rust over a short period of time without causing significant dimensional changes. Austenitic stainless steels such as Cr17Ni7, Cr18Ni9, and Cr18Ni9 may exhibit some rust when exposed to the marine environment. Rust is usually shallow, can be easily removed. 0 Cr 17 Ni 12M 02 Molybdenum-containing stainless steels are substantially corrosion-resistant in marine environments. In addition to the atmospheric conditions, there are two other factors that affect the atmospheric corrosion resistance of stainless steel, namely the surface condition and the manufacturing process. The finishing level affects the corrosion resistance of stainless steel in chlorinated environments. Matte surfaces (matte) are very sensitive to corrosion, ie normal industrial finishing surfaces are less susceptible to rusting. Surface finish levels also affect dirt and rust removal. It is easy to remove dirt and rust from highly finished surfaces but it is difficult to remove them from matt surfaces. For dull surfaces, more frequent cleaning is required if the original surface condition is to be maintained. Freshwater Freshwater can be defined as water that is acidic, salty or slightly salty, originating from rivers, lakes, ponds or wells. The corrosiveness of freshwater is affected by the pH of the water, the oxygen content and the tendency to scale formation. Fouling (hard) water, its corrosive mainly by the formation of scale on the metal surface to determine the number and type. The formation of such scale is the role of minerals and temperature in it. Non-fouling (soft) water, which is generally more corrosive than hard water. Corrosion can be reduced by increasing the pH or decreasing the oxygen content. 1Cr13 stainless steel is significantly more resistant to freshwater corrosion than carbon steel and has excellent features for use in fresh water. Such steels are widely used, for example, for applications requiring docks and dams of high strength and corrosion resistance, however, it should be taken into account that in some cases 1Cr13 may be susceptible to moderate pitting corrosion in freshwater. However, pitting corrosion can be completely avoided with cathodic protection. 1Cr17 and austenitic stainless steels are almost completely resistant to freshwater corrosion at room temperature (ambient temperature). ③ Acidic water Acidic water refers to the contaminated natural water leached from ores and coal and is more corrosive than natural freshwater due to its strong acidity. Acidic water usually contains a large amount of free sulfuric acid because of the leaching of sulfide from ores and coal. In addition, the water contains a lot of iron sulfate, carbon steel corrosion has a very big role. Carbon steel equipment that is affected by acidic water is usually quickly corroded. The results of tests performed on various materials subjected to acidic river water indicate that austenitic stainless steels have a high corrosion resistance in this environment. Austenitic stainless steels have excellent corrosion resistance in freshwater and acidic rivers, especially their corrosion membranes, which have less resistance to heat transfer. So widely used in heat exchange stainless steel pipe. ④ salt water salt water corrosion is often characterized by pitting. For stainless steels, it is due in large part to the local destruction of the passivating film that is resistant to corrosion due to salt water. Other causes of pitting in these steels are the concentration of oxygen in the cell and other seawater organics attached to stainless steel equipment. Once formed, these batteries are very active and cause a lot of corrosion and pitting. In the case of high-speed flow of salt water, such as pump impeller, the corrosion of austenitic stainless steel is usually very small. For condensers using stainless steel tubes, maintain a water flow rate greater than 1.5 m / s to minimize the accumulation of marine organics and other solids in the tubes. For the treatment of salt water stainless steel equipment, the design is best to reduce the gap and the use of thick-walled parts. ⑤ soil buried in the soil of the metal, depending on the weather and other factors, at any time in the complex state of change. Practice has proved that austenitic stainless steel generally has excellent resistance to most soil erosion properties, and 1Cr13 and 1Cr17 in many soils to produce pitting. 0 Cr 17Ni12Mo2 stainless steel is completely resistant to pitting in all soil tests. ⑥ nitric acid chromium not less than 14% of ferritic stainless steel and austenitic stainless steel has excellent resistance to nitric acid corrosion. 1Cr17 stainless steel has been widely used in nitric acid plant processing equipment. However, since 0Cr18Ni9 generally has better formability and weldability, 1Cr17 stainless steel has been largely replaced in the above applications. Other austenitic stainless steels have similar nitric acid corrosion resistance to 0 Cr 18 Ni 9. 1Cr17 stainless steels generally have slightly higher corrosion rates than 0Cr18Ni9, and higher temperatures and concentrations have a greater detrimental effect on them. Hot nitric acid causes intergranular corrosion of austenitic and ferritic stainless steels if the heat treatment of the steel is not appropriate. Therefore, proper heat treatment can be used to prevent this type of corrosion, or stainless steel resistant to this type of corrosion. ⑦ sulfuric acid standard stainless steel grades rarely used in sulfuric acid solution, because of its narrow range of use. 0Cr17Ni12Mo2 stainless steel (the most sulfuric acid-resistant standard grade) is corrosion-resistant at room temperature when the sulfuric acid concentration is less than 15%, or greater than 85%. However, in the higher concentration range, carbon steel is commonly used. Martensitic and ferritic stainless steel generally not resistant to corrosion of sulfuric acid solution. As with nitric acid, sulfuric acid can cause intergranular corrosion if stainless steel is not properly heat treated. For welded structures that can not be heat treated after welding, use a low carbon grade 00Cr19Ni10 or 00Cr17Ni14Mo2, or a stabilized grade 0Cr18Ni11Ti or 0Cr18Ni11Nb stainless steel.

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