Selection of material for liquid ammonia pipelines
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This is an old topic: what material to choose for ordinary liquid ammonia pipelines. Previously, 20# and 16Mn were used, but now 16Mn has been replaced by Q345A~E, and the company no longer allows the use of 20#. As a result, designers opt for the higher-grade materials; 8mm pipes are made from Q345E. Is this really necessary?
The pipes aren’t very clear; it seems that the valves require aluminum bronze or Hastelloy – I’m not entirely sure. Same question
We use both 20 and 16Mn (now Q345E). Looking at the design temperature, sometimes the design temperature for liquid ammonia pipelines is -18°C/-33°C. The most suitable material grade available in China at present is Q345E, as among Q345A–E, only grade E has been tested for impact resistance at -40°C; this is equivalent to the previous 16Mn grade. There is also commonly used liquid ammonia at around 4°C or 10°C; for designs with a temperature requirement of above -20°C, liquid ammonia at 20°C is used. It is important to prevent stress corrosion caused by liquid ammonia; therefore, post-weld heat treatment is required, in accordance with clause 6.3.7 of SH/T3059-2012. Sometimes, the equipment connected to the pipeline is made of 16MnR, and in that case the pipeline is also made of 16Mn.
Last year, I used size 20 for the piping at a liquid ammonia filling station, and there were no problems at all. . . . Why isn’t it allowed to be used? The pipeline standard allows operation down to -20 degrees. . . . .
Ammonia synthesis produces liquid ammonia at around -10°C; the designed temperature is -19°C. As per the manager’s requirements, Q345C was used, but now it is required to use Q345E.
Copper- and zinc-containing metal materials should be avoided in ammonia systems···············
I know that copper-containing materials should not be used in ammonia systems, but is zinc also avoided? The compressed air and domestic water used in ammonia plants are supplied through galvanized steel pipes – doesn’t that pose a problem?
I asked a colleague to do a rough estimation: for liquid ammonia at 20°C, the gas-liquid equilibrium temperature after flashing is roughly -33°C at 1 atmosphere pressure. Should Q345E be chosen considering this situation? I talked to the person in charge of the equipment; they chose 16MnR for use, and it was subjected to impact tests at -20°C, which is equivalent to Q345D as specified in 8163. Of course, its design temperature is determined by the process requirements; ultimately, it is still the process that needs to take into account the throttling conditions. However, for ammonia tanks at normal temperatures, only stress corrosion has been heard of; accidents caused by throttling for cooling have not yet been reported. You mentioned that \"sometimes, the equipment connected to the pipeline is made of 16MnR, and in that case the pipeline is also made of 16Mn.\" "For such pipes, which 16Mn grade do you usually choose?
For the recent liquefied chlorine vaporization process at the company, one section of pipe uses Q345E material, while the rest use 20-grade material
How does 20# steel perform in liquid ammonia pipelines when operating at -33.5 degrees Celsius? Is it insulated?
Compressed air and domestic water belong to the utility systems, and are not part of the ammonia system； When connected, they are separated by flanges and check valves!