Material selection for valves using liquid ammonia as the medium
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I would like to select a safety valve. The working conditions are as follows: the medium is liquid ammonia, in liquid phase; the set pressure is 2.0 MPa, and the discharge temperature is -33 degrees Celsius. Is it acceptable to use WCB? (The book states that the operating temperature range for WCB is -29 to 450 degrees Celsius.) It’s not suitable. What material should be used instead of stainless steel? Thank you!!!!
The most important thing for ammonia valves is good sealing, and we all use babbitt alloy for this purpose
The last edit to this post was made by taishanren on 2010-9-7 at 13:01. When using safety valves for ammonia, it’s actually a good idea to first learn about the characteristics of ammonia stop valves: Ammonia has strong permeability, and moist ammonia gas as well as liquid ammonia containing water can corrode copper, forming green copper-ammonium complexes. Therefore, it is necessary to address the sealing issue properly! No copper or copper alloy seals are required; usually, beryllium copper is welded to seal the valve disc and valve body. Internal leakage generally does not occur. Pure liquid ammonia has very low corrosivity; internal leakage in valves is not caused by corrosion. 1. It is likely due to low hardness or strength of the valve disc and seat, as well as factors such as erosion or damage from particles and indentations. After all, safety valves are not used continuously, and even at low temperatures of -33 degrees, I believe carbon steel (cast steel) is sufficient as a material. 2. The manufacturing process and heat treatment of the sealing surfaces of the valve disc and seat are extremely important. 3. Using stainless steel is unnecessary – it’s not true that the higher the quality of the material, the better. Even with good materials, poor manufacturing processes and heat treatment can lead to problems; however, stainless steel isn’t completely unsuitable either! 4. It is recommended to avoid using cheap valves from small manufacturers; when ordering valves, be sure to specify that the applicable medium is liquid ammonia, as the manufacturer will provide the appropriate valve internals for you. Pure liquid ammonia is non-corrosive, but once even a small amount of water (water vapor) enters, its corrosiveness increases sharply, and it can quickly strip away the hardened layer of the valve core and seat. Feel free to point out any mistakes!
Then I can use babbitt for the valve seat sealing surface and F4 for the valve disc, which will provide better sealing performance and prevent leaks. Is that okay?
Stellite alloy 17-4PH Gr13 Monel alloy
The valve body is made of low-temperature steel LCB, while the valve disc and the valve seat of the body are welded from beryllium copper
The valve body is made of WCB, while the valve seat and valve disc are made of beryllium copper
Could 16MN be considered?
WCB valve body; babbitt alloy can be used for the rest
The valve body is made of low-temperature carbon steel, while the valve seat is made of babbitt
The A42Y-C series can be selected; its sealing surface is made of Stellite alloy deposited by welding.