The influence of temperature and concentration on chloride ion corrosion
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Since I often encounter problems related to chloride ion corrosion in my work, there are many different opinions available online; people explain various principles, but they fail to clarify how to apply them. Therefore, I hope that someone in this highly specialized field can help me understand these issues. The questions are as follows: 1. Selection of electrode material for electromagnetic flowmeters: At normal temperature, when the chloride ion concentration is ≤10000 ppm, titanium electrodes should be used ； If the chloride ion content is >10,000 ppm, should a tantalum electrode be used? Is there any problem with that? When the temperature is between 100 and 150°C, 10,000 ppm serves as the threshold: titanium electrodes should be used when the concentration is ≤10,000 ppm, and tantalum electrodes when it’s >10,000 ppm. Is there any problem with this approach? 2. Sometimes, when the chloride ion content is mentioned, only a concentration of 1% is given. Does this 1% correspond to 10,000 ppm?
Additional question: The chloride concentration in the pipeline circulating water is 1000 mg/L, and the sulfate concentration is 2000 mg/L, at room temperature. Due to the high concentration of chloride ions, 316L material was chosen for the pipes; it is not clear whether this material can resist corrosion caused by chloride ions. However, I came across the following statement online: “A method to suppress chloride-induced corrosion in circulating cooling water involves adding sulfates in an amount equal to 0.5–1.8 times the concentration of chloride ions present, thereby fully passivating the surface of stainless steel. Scale inhibitors are also added to prevent scaling.” The sulfate referred to is one of sodium sulfate, potassium sulfate, or magnesium sulfate, or a mixture of two or more of these substances; the amount of sulfate added is 0.5-1.8 times the concentration of chloride ions. ” May I ask: Does the presence of sulfate ions inhibit the corrosion of stainless steel by chloride ions, and what is the mechanism behind this?