Regarding the selection of instrument tubing
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The materials used for the instrument pipes before and after the primary valve in the main steam pipeline of ultra-supercritical units are different. According to available information, the temperature behind the primary valve is much lower than that in front of it. However, the length of the instrument pipe in front of the primary valve is usually only about one meter. Why is the temperature behind the primary valve lower than that in front of it? And if the drain valve is opened and fluid flows through, shouldn’t the temperatures before and after the primary valve be the same? Why are different materials used for the instrument pipes on each side of the valve?
All valves have a throttling effect, which results in a lower temperature downstream of the valve; however, the same material is chosen for them.
Do you mean that super-supercritical technology is used for treating wastewater?
At the steam outlet, the temperature drops significantly due to the lack of gas flow, but the material of the pipe should be the same as that of the pipe before the primary steam valve, or slightly higher
1. When the medium does not flow, the heat exchange rate decreases. 2. The heat conduction rates vary depending on the material; heat conduction refers both to the transfer of heat from one place to another and to the transfer of heat from cold to hot. 3. There is no requirement that the materials on the upstream and downstream sides of the valve must be different. The principle remains the same: either the gauge pressure material is of higher quality than the piping material.
The pressure tap on the instrument does not need to be cleaned frequently; as long as there is no leakage, it’s fine