Determination of design temperature

Determining the design temperature requires considering various factors, such as the properties of the medium, operating conditions, and the heat resistance of the materials. Generally, the design temperature should be slightly higher than the operating temperature of the medium, to ensure that the equipment does not overheat or undercool during normal operation. Given that the operating temperature of the medium you provided is -20°C to 40°C, it is recommended to choose a design temperature of around 50°C to 60°C. As for whether it is feasible to use Q345R as the material, an assessment needs to be made based on the specific application scenario. Q345R is a commonly used steel material for pressure vessels, possessing excellent properties such as high-pressure resistance, heat resistance, and corrosion resistance. However, it is important to ensure that its operating temperature meets the design requirements, and an assessment should be carried out taking into account the characteristics of the medium involved. If more stringent requirements exist, other materials such as 304/316 stainless steel can be considered. -

The medium temperature is in the second and third rows of this table; I’m not sure whether to choose the higher value or the lower one

Based on the information you provided, the medium temperature falls between the second and third rows of the table; it is recommended to choose the higher value as the design temperature. This is because the temperature of the medium fluctuates to some extent during normal operation; if a lower design temperature is chosen, the equipment may not function properly when the medium temperature reaches its peak, which affects production efficiency. Choosing a higher design temperature ensures that the equipment can operate properly for most of the time, while also providing a margin to cope with changes in the temperature of the medium. Of course, the selection of the specific design temperature also takes other factors into account, such as the heat resistance of the material and the temperature of the operating environment. -

Where does it come from? The medium temperature ranges from -20°C to 40°C℃

If the minimum operating temperature is determined to be -20°C, then the minimum design metal temperature can also be set at -20°C; in this case, Q345R can be used, but it is necessary to specify the low-temperature impact temperature and the corresponding acceptance criteria in accordance with the requirements of the material section of GB/T150. The design temperature should be determined reasonably based on the maximum operating temperature, which is used for strength verification.