Are potassium nitrate and sodium nitrate considered intergranular corrosion agents?
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There are two conditions for intergranular corrosion. 1 is temperature: austenitic stainless steel lean region of 450~850 ； 2 is the medium: some oxidizing media. Is my understanding correct? The molten salt medium used in the concentrated solar power industry is commonly a binary salt (40% KNO3 + 60% NaNO3). The device temperature is around 550; the temperature conditions are met. Are the medium conditions met?
Does a medium in an electrolytic state (soluble in water or in a high-temperature molten state) necessarily undergo electrochemical corrosion?
Hehe, I met a colleague who works in the field of photothermal technology here. Please send me the detailed information to my email address wj920278@163.com, and I’ll pass it on to the colleagues at Taiyuan Iron and Steel’s technology center so they can help you look into it. Which grade of stainless steel have you chosen? 321? 347H？
When working with pressure vessels, it is important to follow the standards regarding intergranular corrosion. The medium in question should be assessed using GBT 21433-2008, the standard for testing the susceptibility of stainless steel pressure vessels to intergranular corrosion, in order to determine whether there is a tendency toward intergranular corrosion. The standards clearly specify which media require such testing to identify any potential for intergranular corrosion.
The factors that affect the corrosion of stainless steel include those related to the medium: temperature, concentration, and pressure. Although potassium nitrate and sodium nitrate are not corrosive to stainless steel, it is necessary to consider the content of chloride ions in nitrates. Even if the chloride ion level is low, it still needs to be taken into account at a temperature of 550 degrees Celsius, especially at the welding points of heat storage tanks and pipes; acid washing and passivation should be carried out after welding. The cause of the molten salt leak at Crescent Dunes in the United States has not been disclosed to date, but reports indicate that the leak occurred at the welds. When the temperature of the molten salt reaches 550 degrees Celsius, it is likely to be tower-type concentrated solar power generation. In the Delingha project, 347H stainless steel was used for the tanks, while in the Dunhuang project, 625 stainless steel was used for the pipes.
Hello, can 316 be used? Why? Thank you!
This post was last edited by bxgsx on 2018-1-9 at 11:15. When exposed to an environment of 560 degrees Celsius for an extended period, stainless steel is prone to intergranular corrosion. Prevent intergranular corrosion: 1. Reduce the time at 450~850 degrees Celsius to minimize the formation of chromium carbide ； 2. Ultra-low carbon stainless steel is used, resulting in insufficient carbon to form chromium carbide ； 3. Choose stainless steels containing titanium and niobium; 321 contains titanium, while 347 contains niobium. Titanium and niobium are more reactive than chromium, and they react with carbon preferentially to chromium. Where does the original poster plan to use 316? A molten salt heat tank? Several people in the domestic CSP sector I have come into contact with prefer 347H. It’s not clear why they choose 347H, which has a high carbon content; after all, we only deal in stainless steel pickling and passivation products, and we are not involved in the design or construction of CSP systems. My capabilities are limited; I can only explain up to this point.