Can flanges of different weight classes be connected to each other
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HG/T20592 specifies that when the two flanges in a flanged joint have different pressure-temperature ratings, the rating of such flanged joint shall not exceed the lower one among them. SH/T3059 stipulates that when flanges with the same connection dimensions and pressure rating but different pressure-temperature ratings are connected, the operating conditions shall be determined based on the flange with the lower pressure-temperature rating. What is unclear is whether the two flanges in HG’s table refer to those of the same weight class but different materials, or whether they can also be used for different pressures while having the same external dimensions Is there anyone who knows for sure?
Flanges of different weight classes cannot be butt-welded in principle. The connecting flanges are required to meet the same standards, have the same pressure rating, and the same bore size.
The regulations for the two standards are the same.
It is necessary to apply knowledge flexibly and not stick rigidly to rules. Some flanges under different pressures have the same dimensions; such cases do exist, but there are many cases where they differ. Materials at different temperatures cannot be identical. As long as two of them can be connected when used together, or some way can be found to connect them, it is possible – of course, provided that no problems arise. It is sufficient to ensure that the pressure or temperature is low enough to meet the operational requirements
Parameters such as the bolt hole diameter, the diameter of the bolt hole circle, and the dimensions of the sealing surface remain the same; only parameters like pressure, temperature, and material vary. The operating conditions should be based on the flange with the lower pressure-temperature rating.
There’s no need to worry too much about this; the flange specifications should be matched according to the higher pressure, and the material used for one side can be chosen as one suitable for low temperatures.