Corrosion issues with 1% sodium hydroxide
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Dear sea friends, I have a question: for a 1% sodium hydroxide aqueous solution, the normal operating temperature is 142°C and the operating pressure is 0.6 MPaG. Is it feasible to use 304 material in this case? Would it be more appropriate to use 316L instead? Thank you!
It works fine, but attention should be paid to the chloride content in the liquid alkali. Generally, the chloride ion content in liquid caustic is quite high. I wonder if using 310S would be better.
Appendix D of SH/T3059 specifies that when the temperature of the alkaline solution exceeds 100°C, nickel-based alloys are recommended; for such temperatures, plastic-lined pipes could be considered, as austenitic stainless steel still poses a risk of stress corrosion cracking
Thank you for providing the information. I have always thought that this diagram is ambiguous; in my opinion, it should refer to an alloy containing Ni, rather than a nickel-based alloy.
This is the original source of the alkali corrosion curve in the appendix of SH/T3059; in my opinion, the nickel alloys mentioned there refer to alloys containing nickel, rather than nickel-based alloys.
The figure below shows the corrosion curves of 304 and 316 in alkaline solutions as presented in the Handbook of Corrosion Data; however, 304 and 316 are shown on the same graph. Based on experience, 316 has much better corrosion resistance in alkaline solutions~
It really depends on individual interpretation; in the older version of the SH 3059, it states that for the nickel-based alloy area, either MONEL alloy or 18-8 austenitic stainless steel can be used. For temperatures above this level, we mostly use lined pipes; nickel-based alloys are too expensive, and we didn’t dare use 304 or 316L. In terms of corrosion resistance, 316L should be better than 304
Materials such as liquid alkali + high chloride ions, duplex steel, and 2205 are better than 316L
316L stainless steel with a sodium hydroxide concentration of <20% can be used just fine. From an economic perspective, it is recommended to use PE-lined steel
What material should be used if the sodium hydroxide concentration is <32%?
For temperatures below 80°C, a steel-lined PP is used; for temperatures above 80°C, a steel-lined F4 is employed.