How should the material of pipes and fittings, as well as the design pressure and design temperature, be selected for liquid ammonia and other process fluids? ?

Based on experience, these parameters need to be calculated according to your specific process. For example, it is necessary to determine what flow rate is required for liquid ammonia and at which point it should evaporate into a gas; only based on this information can the material of the pipes and the design pressure be determined

Could some experts answer separately? 1. When the pipeline carries liquid ammonia. 2. When the pipeline carries gaseous ammonia. 3. When there is vaporization in the pipeline. 4. When there is liquefaction in the pipeline. Should the ambient temperature be considered as ranging from -20 to 40 degrees?

For common media, there is generally a recommended flow rate, which is determined by taking into account both economic factors (a higher flow rate allows for a smaller pipe diameter, resulting in lower costs) and technical factors (a larger pipe diameter results in less pipeline resistance). For liquid ammonia, the flow velocity varies depending on the pressure range: In vacuum conditions, the flow velocity is 0.05–0.3 m/s; too high a flow velocity can lead to a two-phase flow (gas and liquid), resulting in significant losses in vacuum level. This requires sophisticated vacuum equipment and is not economical. At pressures below 0.6 MPa, the flow velocity is 0.3–0.5 m/s; at pressures between 1.0 MPa and 2.0 MPa, it is 0.5–1.0 m/s (I usually use 0.8 m/s as a value). Similarly, for gaseous ammonia, the flow velocity varies with pressure: in vacuum conditions, it is 15–25 m/s at 0.1–0.2 MPa (absolute pressure); it is 8–15 m/s at 0.35 MPa (absolute pressure); and 10–20 m/s at pressures below 1.0 MPa and 2.0 MPa. At these pressures, the flow velocity is 3.0–8.0 m/s (I usually use 4 m/s as a value). In situations where liquid ammonia is prone to vaporization, it is advisable to use larger-diameter pipes in order to reduce the flow velocity, as two-phase flow results in high resistance losses. In the case of liquid ammonia condensation, this generally occurs in heat exchange applications, such as the condensation of high-pressure gaseous ammonia at the outlet of refrigeration units; water cooling is commonly used for this purpose. For a cooling water temperature of -5 to 20°C, the corresponding condensation pressure ranges from 3.62 to 8.742 MPa (absolute pressure). A flow rate of 0.5 m/s in the outlet pipeline of the water cooler is considered appropriate. Regarding the pipe material, for liquid ammonia pipes, the main concern is addressing low-temperature issues; using 16Mn is suitable within a temperature range of -40°C to 50°C. If the temperature is within the range of -20°C to 50°C, using 20# steel should also work. I hope the explanation above can be helpful to the original poster and the friends who commented above. This post was last edited by Li Yiheng on 2008-1-18 at 15:14.]

The liquid ammonia pipelines in our facility are made of 16MnR seamless carbon steel pipes; copper-based valves cannot be used, and we generally opt for babbitt alloy valves

What was said upstairs is correct; currently, the valve body material for ammonia valves is generally cast steel, while babbitt is often used as the material for the valve seat sealing surface. Liquid ammonia corrodes copper (by forming copper-ammonia complex ions), so neither the valves nor the pipes can be made of copper.

The valve ratings for ammonia are all above 2.5 MPa. I wonder if it includes gaseous ammonia mixtures and ammonia water?

Generally, the flow rate of liquid ammonia/gaseous ammonia should be kept as low as possible to prevent the vaporization of liquid ammonia; the pressure should be above 2.5 MPa, and the materials commonly used are 20# and 16Mn

Back to floor 8: The valve ratings for ammonia are all above 2.5 MPa, including 2.5 MPa itself. The reason for this is that at an ambient temperature of 40°C in summer, the pressure at the gas-liquid equilibrium of liquid ammonia is close to 1.6 MPa; therefore, it is necessary to use pipes and valve fittings with a rating at least one level higher to ensure safety. It is not necessary for gaseous ammonia mixtures and ammonia water.

What criteria should be used when selecting the grade for fluid pipelines?

The pipeline grade for fluids is determined by the temperature and pressure of the fluid medium, in order to meet the requirements related to the maximum operating pressure of the process fluid