What are the requirements for instrument air dew point?
Thread Content
Regarding the requirements for the dew point of instrument air, HG/T 20510-2014 states that the dew point under the operating (online) pressure of the air supply system should be at least 10°C lower than the local annual (seasonal) extreme minimum temperature in the working environment or in historical records. How should this sentence be understood? How to operate it? For example, if the historical extreme minimum annual (seasonal) temperature in that area is -30°C, what should be the dew point requirement for the instrument air? Is it a requirement at atmospheric pressure, or at the operating pressure? Could you give an example, please?
1.-40℃ 2. It refers to the dew point at the operating pressure; for example, if the lowest annual (seasonal) temperature recorded in a region over time is -30℃ and the pressure of the gas used in the instrument is 0.7 MPa (refer to the conversion table in HG/T 20510-2014 for normal pressure and operating pressure), then the dew point at the operating pressure should be at least -40℃℃
The standards specify clearly that the dew point under the operating pressure of the gas source should be 10°C lower than the lowest ambient temperature.
It means that the dew point is 10 degrees lower than the local minimum temperature; in other words, it’s 40 degrees
This post was last edited by marry on 2016-3-3 09:35. It should be 10 degrees lower than the lowest ambient temperature; for example, if the lowest ambient temperature is -30, then I require the dew point temperature of the instrument air to be -40. What pressure does this refer to? When talking about dew point, it is necessary to specify the pressure at which it is measured. The required pressure for instrument air is 0.4~0.7 MPa, so the dew point also falls within a certain range.
In other words, the measured dew point under operating conditions should be 10 degrees lower than the extreme minimum temperature. There are now portable dew point meters, making online measurements very convenient!
The original poster and the others have all explained it in great detail. Additionally, at the several factories where I have worked, the instrument air pressure was always between 0.6 and 0.7 MPaG, and the dew point requirement was below -40 degrees Celsius.
The extreme minimum temperature is -30°C; therefore, the pressure dew point of the instrument air must be at least -40°C, with the corresponding atmospheric pressure dew point being around -57°C. The dew point meter measures the dew point at atmospheric pressure; I hope there is no confusion regarding this