Case analysis of radar level gauges in liquid ammonia applications

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Liquid ammonia, as one of the **designated major hazard sources**, is, under normal conditions, a colorless gas with a pungent odor; it can be easily liquefied. When the temperature rises or the pressure decreases, liquid ammonia can evaporate rapidly, absorbing a large amount of heat in the process. Since liquid ammonia is somewhat corrosive, it also has a high toxicity. There are two good methods for measuring liquid ammonia in industrial settings: one is measurement using a radar level gauge, and the other is external level gauge measurement. This article mainly presents an analysis of the use of radar level gauges in liquid ammonia applications. Ammonia water has a certain corrosive effect, and ammonium carbide is even more corrosive; it can easily cause damage to equipment such as pipes and valves, leading to ammonia leaks. Ammonia can burn the skin, eyes, and mucous membranes of the respiratory organs; excessive inhalation of it can cause lung swelling, leading to death. The explosive limit of ammonia is 16–25% (with a concentration of 17% being the most prone to ignition). It also has numerous applications in the industrial sector. However, with the widespread use of liquid ammonia, some companies fail to provide proper supervision over it, which can easily lead to many accidents resulting in numerous deaths and injuries. The difficulties in using radar to measure liquid ammonia lie in the following points: the large amount of vapor it produces attenuates the radar signal. The greater the storage pressure, the higher the steam density, and the more severe the signal attenuation becomes. For this operating condition, guided wave radar or coaxial guided wave radar level gauges are more suitable, as guided wave radar uses low-frequency pulses, resulting in the weakest signal attenuation in environments with a large amount of steam. Therefore, compared to contactless radar, guided wave radar is more suitable. As shown in the image below: http://www.dhechina.com/ueditor/php/upload/image/20220704/1656916682511517.png Another challenge is the corrosiveness of liquid ammonia; it has a certain degree of corrosive property. It particularly easily corrodes rubber materials. Therefore, the material selection for the instrument’s sealing ring is a very important issue. The author once installed a radar level gauge with a seal made of ordinary material in an ammonia liquid operating environment. During the first month after it was installed, the dashboard worked properly the whole time. Starting from the second month, users found that the gauge was not working properly, and later on it simply went black. Upon arriving at the site, it was found that the electrical circuitry of the instruments had been corroded by ammonia, indicating that there had been an ammonia leak. After removing the gauge and sending it back to the company for repair, it was found that the seal ring between the gauge’s sensor and the circuit chamber had completely corroded away. After that, a new seal ring made of material resistant to liquid ammonia corrosion was installed, and the instrument has not experienced any further failures. As shown in the figure below, the resistance of ordinary rubber and fluororubber to liquid ammonia corrosion is rated at level D, which is the weakest level and indicates that they are completely unsuitable for use. Chloroprene rubber and nitrile rubber are classified as Grade A and Grade B, both of which fall within the acceptable usage categories. Therefore, the material of the sealing rings used in liquid ammonia applications must be chloroprene rubber or nitrile rubber. http://www.dhechina.com/ueditor/php/upload/image/20220704/1656917153232143.png