Why are the pressure rating specifications for pipe flanges in GB 50341 set so high?
Thread Content
As specified in 10.1.4, the pressure rating of the steel flanges used for openings in the tank wall should not be lower than 1 MPa, while the pressure rating of the steel flanges used for openings at the top of the tank should not be lower than 0.25 MPa. In GB50341, the pressure required for storage tanks is so low; then why is the pressure rating for steel pipe flanges so high? I hope the experts here can give me some advice!
Among the commonly used flange standards, there is no pressure rating lower than 0.25 MPa； As for setting the flange pressure for the tank wall connections at 1 MPa, this seems to be based on past experience – under external forces acting on the pipes, flanges with lower pressure ratings are more prone to leaks. It seems that for manholes, where there are no such external forces on the pipes, a pressure of 0.6 MPa could be used. In fact, the cost of this flange is negligible compared to the overall cost of the tank; there’s no need to create a potential hazard just to save a few thousand dollars. Any subsequent repairs would involve shutting down operations and carrying out cleaning tasks, and those aren’t things that can be resolved with a small amount of money.
A pressure rating of 1.0 MPa is likely to be commonly used for the flanges on the tank wall connections; if the medium is explosive, a higher pressure rating will be employed. The wall thickness of the pipe fittings themselves is also greater than that of ordinary equipment; for pipe fittings larger than DN50, reinforcing rings are required as well. It is mainly to prevent large tanks from leaking due to the connection flanges; one should not lose the big picture because of minor issues.
There is also external force on the piping connections of pressure vessels, and none of the pressure vessel standards require that the flanges on these connections have a pressure rating much higher than that of the vessel itself. As mentioned on the 3rd floor, GB50341 requires the use of reinforcement rings for connectors with a diameter larger than DN50; in fact, there are many other aspects where GB50341 has stricter requirements than GB150. I’m not sure why
1. Even in pressure vessels where the medium is explosive, there is no requirement that the pipeline pressure rating be much higher than the design pressure of the vessel. 2. I’m not sure if your company adds reinforcement rings to all the connections of storage tanks larger than DN50
First question: Section 7.2.3 of HG/T20583-2011 specifies that the nominal pressure class of the flanges for connections to explosive media should be no less than 1.6 MPa. When it comes to flanges, gaskets are also a relevant consideration; metal wound gaskets are often used for this purpose. The nominal pressure class of HG/T20610 wound gaskets is at least 16, which corresponds to 1.6 MPa. Second question: Reinforcement rings will be added to the nozzles on the tank wall with a diameter larger than DN50.
Yes, for flammable, explosive, highly toxic, and extremely toxic media, the minimum PN is 16.