Can valves used in liquid ammonia media be replaced with ordinary steel valves?
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This post was last edited by adsl121 on 2009-9-3 02:02. Valves for liquid ammonia media are generally ammonia valves, but it is not clear whether ordinary steel valves can be used as substitutes; I would appreciate everyone’s advice.
Liquid ammonia can be replaced with a regular gate valve, as such valves can withstand the freezing point of liquid ammonia.
Sure, but it should be made of cast steel, with the sealing surface made of stainless steel.
Theoretically, liquid ammonia does not corrode carbon steel, but if water is present in it, that is, when it is not 100% pure liquid ammonia, corrosion may occur. Therefore, under normal circumstances, the approach we adopt is to use carbon steel valves with stainless steel sealing surfaces, rather than so-called all-stainless steel valves.
It is best to use it according to the medium suitable for the valve
Valves for liquid ammonia must be selected carefully, as leaks can cause serious problems; it is best to use valves designed specifically for liquid ammonia
This post was last edited by ZZJJAA70 on 2009-11-16 at 20:34. For valves used in liquid ammonia media, ammonia-specific valves are the best choice; such valves feature special measures for their sealing gaskets and flange sealing surfaces.
The manufacture of ammonia valves requires stricter standards than those of ordinary globe valves. When comparing ammonia valves with regular globe valves on the production site, it can be seen that ammonia valves have longer packing and thicker packing glands; this is to prevent the glands from coming loose, which could lead to ammonia leaks and accidents. I think ordinary valves should not be used as substitutes for those in ammonia-based media, as the risk of accidents is higher.
The valve core of the liquid ammonia stop valve is made of babbitt, a very soft material that provides excellent sealing performance； The material used for valve bodies was originally malleable cast iron; nowadays, cast steel is generally used ； Flanges used to have male and female surfaces, but now there are also those with male surfaces only. It is also possible for some manufacturers to use a stainless steel valve core of one higher grade as a substitute, but the packing must be compatible. One thing to be absolutely careful about is not to use copper or copper alloy valve cores; doing so can lead to serious problems. In particular, valves made of copper alloy materials are easily confused by maintenance personnel (including technicians). Based on experience, it is generally not a problem to use higher-grade materials in place of lower-grade ones; but in this case, it is indeed a big mistake.
In fact, whether you choose valves made of ammonia-resistant materials or those with stainless steel internals, I think it’s necessary to analyze the cost of use. The price of ammonia-resistant stop valves is not very high; whereas those with stainless steel internals may be more expensive. It is recommended to opt for ammonia-resistant valves unless it’s an emergency situation.
It shouldn’t be replaced; the valves designed for ammonia take advantage of the characteristics of ammonia systems, and they cannot be used interchangeably. Ammonia storage tanks hold large quantities of ammonia, and the risk associated with this is very high; the consequences of an ammonia leak would be catastrophic. Valves used for ammonia should have appropriate materials, stable performance, good sealing properties, and be tightly sealed. Lead-lined valve stems can be repaired and inspected annually, while stainless steel valves cannot be repaired. Therefore, I recommend that ammonia systems also use valves designed specifically for ammonia use.