Issues regarding the operating pressure of manholes per HG/T21521-2014
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What is the reason for the difference between the maximum allowable operating pressure at the operating temperature for Class V materials as specified in HG/T21521-2014, and the maximum allowable operating pressure for the flange materials (1C1) as specified in HG/T20592-2009? Since the forgings are made of 16MnDIII, and according to the pipe flange standards, material 1C1 allows a maximum allowable operating pressure of 40 bar at 100°C for PN40 grade. Meanwhile, for material of category V under standard 21521-2014, the maximum allowable operating pressure for PN40 grade at 100°C is 39 bar. The design pressure of the equipment is 4 MPa, with a design temperature of 60°C. Can we ignore the requirements of the manhole standards just because they are met by the pipe flange standards?
I hadn’t noticed this issue before. Since manholes have requirements regarding the maximum allowable operating pressure, you should meet those requirements. If it doesn’t meet the requirements but you still want to use it, then non-standard calculation verification is required. But what interests me more is what the pressure rating is for the flange used to connect your equipment
Since a standard manhole has been chosen, it naturally has to be constructed in accordance with the standards for manholes. As a component, the maximum allowable operating pressure for an access hatch cannot be determined solely based on the capacity of the flanges; it is the result of a comprehensive consideration.
It can be attributed solely to the different organizations responsible for formulating these standards. Many of the standards regarding manholes are actually derived from older standards; the data in them has not been updated in line with any revisions to relevant standards, which is why this situation occurs.
I don’t think it’s possible; both standards must be followed unconditionally. Following strict selection criteria.
For Category V materials in 21521-2014, in addition to flanges made of 16MnDIII, there are also flange covers made of 16MnDR. In the standards for pipe flanges, 16MnDR corresponds to material 1C3; its maximum allowable operating pressure at a pressure rating of PN40 and at 100°C is 39 bar.