What is the degree of corrosion of 304 stainless steel by domestic wastewater, whose pH value is 6-9? Please help to answer this. Thank you very much.
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What is the degree of corrosion of 304 stainless steel by domestic wastewater, whose pH value is 6-9? Please help to answer this. Thank you very much.
With such a question, the original poster, maybe no one will be able to answer you. The pH value is determined by the concentration of hydrogen ions and hydroxide ions. However, the corrosion resistance of 304 stainless steel in solutions is primarily influenced by the concentration of chloride ions. In fact, in a neutral salt spray environment (a sodium chloride solution with a pH of 7), even if 304 stainless steel has been surface-passivated to enhance its corrosion resistance, it generally cannot withstand more than 48 hours of exposure. Generally speaking, it is believed that qualified 304 stainless steel can resist acid and alkali corrosion within a pH range of 4 to 10 when the chloride ion concentration is low. 304 stainless steel has little problem resisting alkaline corrosion; as for its ability to resist corrosion caused by hydrogen ions at a pH of 3, it’s difficult to say without conducting specific tests (in my experience, high-quality 304 steel produced by reputable manufacturers can still withstand such conditions. However, the quality of 304 stainless steel in China varies greatly, so it’s not possible to make generalizations).
It’s useful to consider the purpose of use and the designed service life; carbon steel with an anti-corrosion coating is more commonly used in sewage treatment projects.
With only the pH value as a piece of data, it is certainly impossible to determine the rationality of the material selection. Typically, sewage contains high levels of CL ions; if there are also high levels of other impurities or microorganisms that affect corrosion, 304 is likely not sufficient.
pH 6–9: One should first understand that pH refers to the concentration of hydrogen ions... and it does not necessarily indicate corrosive properties. A pH range of 6–9 is basically neutral, with weak corrosive capacity. However, if chloride ions are present in sufficient concentrations, they can cause corrosion in stainless steel (more precisely, they can lead to the formation of pinholes)