Questions regarding the calculated temperature of boilers
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I would like to ask about the calculation temperature when using 16508 to perform strength calculations on boilers. Assuming a boiler with a pressure of 1.25 MPa, and the calculation pressure is 1.3 MPa, what is the corresponding calculation temperature? My approach was to use a thermometer that shows 1.3 + 0.1 = 1.4 MPa, and the calculated temperature came out to be 195.04°C. However, I’ve never understood what the basis for this is – where does it state that an additional 0.1 MPa needs to be added? Which standard specifies the method for calculating temperature? I had always thought it was this method, because in other places I encountered situations where the value wasn’t 195.04; there was no way to refute the claim that their calculated temperature was incorrect, nor could I prove that my own calculated temperature was right. So I want to find a basis for calculating the temperature.
The temperatures in different parts of the boiler vary; who knows which one you need to calculate?
Using this calculated pressure of 1.3 MPa, the rated average temperature of the medium can be found by consulting a table; such tables provide temperatures corresponding to absolute pressure. Since 1.3 MPa is a relative pressure, it needs to be adjusted by adding 0.1 MPa, which is the value of one atmosphere. Absolute pressure (MPaG) = Relative pressure (MPaA) + 0.1
After adding 0.1 MPa, the calculated temperature obtained from the tables has little effect on the allowable stress, and essentially no impact on the chosen thickness
The most fundamental temperature is the one used for calculation; all other temperatures are derived from this value by adding 25 or 70°C, etc.
Can this temperature selection be used as a reference?
There are slight differences between curve fitting and ready-made tables. Believe in yourself.
Generally, the error in curve fitting that is considered acceptable is within a few decimal places, and can be completely ignored. The temperature reading given by the Borel software was 0.3 higher. At first, he insisted on talking nonsense about what height of liquid column corresponded to the atmospheric pressure, but I showed him the values: 194.3 for the cylinder and 194.04 for the collector box, and only then did he admit that they should be the same.
Buller, the more you use it, the more problems you find. Many factories have started using custom-made documents.
By distinguishing between gauge pressure and absolute pressure, the aforementioned problem can be easily resolved.