Regarding the issue of the pipeline diameter downstream of the safety valve
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I’m a novice designer, and I would like to ask the more experienced colleagues here a question regarding the pipe diameter downstream of a safety valve. For example, in the case of a tank with the maximum capacity, if the operating pressure at which the safety valve opens is 0.95 MPaG and the back pressure downstream of the valve is at atmospheric pressure, then based on the volume of gas that needs to be released, the inlet diameter of the safety valve should be DN40 while the outlet diameter should be DN50. If a DN50 pipe is connected downstream of the valve, as the gas pressure drops from 0.95 MPaG to atmospheric pressure, the flow velocity of the gas exiting the pipe could reach several hundred meters per second. Moreover, a colleague in my department said that the diameter of the main discharge pipe should be determined based on the discharge capacity of the largest safety valve; would that mean the main pipe would also need to be DN50? I wonder how the experts here think about this pipe diameter? Thank you all
Could you explain in detail how the DN40 inlet and DN50 outlet of the safety valve, as determined based on the discharge volume, are calculated? ? The gas volume expands behind the safety valve, resulting in an increased natural flow rate; therefore, the main pipe must be large enough. I would like to ask how the DN50 size of your outlet was determined? Based on your imported DN40 specification, it seems that the outlet main pipe for the safety valve should be around DN150 to DN200.
I calculated the throat diameter of the safety valve based on the discharge volume, and then selected the corresponding safety valve model. The specifications for that model state that its inlet flange is DN40 and its outlet flange is DN50. Do you mean that the pipe after the outlet flange should be expanded to DN200, or should a straight pipe of DN50 be connected to the DN200 discharge main?
When the DN50 fitting is inserted into the DN200 main pipe, the back pressure at the outlet has not actually decreased by the time the safety valve opens, so it is still possible to arrange it according to the DN50 standard, inserting it at a 45-degree angle from above into the DN200 main pipe.
The outlet pipe needs to be expanded; expanding it by one or two grades is sufficient, and for larger volumes, it can be expanded by several more grades
Well, that’s also why our review required me to insert the pipe at a 45-degree angle into the main pipe – that’s the reason. Thank you, expert!
The size of the outlet pipe must be calculated precisely; the Mach number for discharge into the atmosphere should be less than or equal to 0.5, while the Mach number for discharge into a sealed system should be between 0.5 and 0.7. The calculation method can be found in HG20570.2-95. It is recommended that the original poster do the calculations themselves to reinforce their memory.
The size of the outlet pipe must be calculated precisely; the Mach number for discharge into the atmosphere should be less than or equal to 0.5, while the Mach number for discharge into a sealed system should be between 0.5 and 0.7. The calculation method can be found in HG20570.2-95. It is recommended that the original poster do the calculations themselves to reinforce their memory.