How to select the pressure rating for HGT20592 pipe flanges? ? ?

If the drawing specifies a maximum allowable operating pressure, it should be taken into consideration.

According to the basic codes for the design of chemical containers, the maximum allowable operating pressure is the minimum allowable pressure for the load-bearing components as calculated for the container. The operating pressure is the highest pressure that can be reached at the top of the container, and the design pressure must be higher than the operating pressure; therefore, it is correct to determine the flanges based on the design pressure.

This post was last edited by xlxuiin on 2019-6-6 at 16:55. How to understand the maximum allowable operating pressure? Applying the relevant regulations for pressure vessels: Such pipelines generally have the following requirements – the medium involved is hazardous, and emergency relief devices must be installed. According to the regulations for pressure pipelines, such pipelines need to undergo pressure testing, with the test pressure set at P=1.5Pset. Therefore, P=3.5*1.5=5.25 MPa. Hence, choosing PN40 is not appropriate. The setting of the aforementioned maximum allowable operating pressure is merely intended to facilitate pressure testing of the pipes, and this pressure occurs only occasionally and intermittently (it is not a continuous operating pressure); it has nothing to do with the choice of flanges.

The reason is that it’s true that \"when selecting a pipe flange, the pressure rating only needs to be determined based on the design pressure of 3.5 MPa, without taking into account the maximum allowable operating pressure,\" but he overlooked the pressure testing.

This post was last edited by gn_1984 on 2019-6-17 at 11:30. The maximum allowable operating pressure must be taken into consideration, but the nominal pressure class of the pipe flange is not determined by the maximum allowable operating pressure. Without considering the maximum allowable operating pressure, the nominal pressure class of the pipe flange is determined based on the operating pressure (for safety reasons, it is generally determined based on the design pressure during design). Please note: for the hydrostatic test, the maximum allowable operating pressure is 1.25XP, and the allowable stress coefficient at that temperature is greater than or equal to 5.13 MPa. The original poster should check what the maximum allowable operating pressure is for PN40 pipe flanges under these pressure and temperature conditions; assuming it is 4.0, then 1.5X4 = 6.0 MPa. Since the hydrostatic test pressure of 5.13 MPa is less than 6.0 MPa, it is reasonable and correct to choose PN40 for the pipe flanges. PS: I haven’t looked at it in detail yet, but for a maximum allowable operating pressure of 4.1 as specified by the poster, choosing PN40 is clearly not appropriate. Therefore, with an operating pressure of 2.5, PN40 should be fine. The maximum allowable operating pressure specified by the poster should not exceed the maximum allowable operating pressure corresponding to the design temperature of the PN40 flange – that’s what’s appropriate.

It is best to allow the allowable operating pressure to be the minimum value obtained from all the stressed components; in other words, the highest allowable operating pressure can be used as the design pressure, from which all components can be checked.

The maximum allowable operating pressure indicated on the drawings is intended for airtightness testing and is of a hypothetical nature; in reality, this pressure can never be achieved. But since it is indicated on the drawings, that is to say, the equipment is capable of withstanding such pressure, therefore this maximum allowable operating pressure must be used as the design pressure. From this, the strength of various pressure-bearing components as well as the reinforcement required for openings must be calculated. It is absolutely necessary to do this; experts have stated this in every renewal process. As for choosing the flange, there seems to be controversy regarding whether to opt for 40 MPa or 63 MPa.

This post was last edited by zhangjuhua on 2019-6-7 at 19:48. It seems that the safety aspect of PN40 is not an issue; as mentioned above, it can withstand a pressure of up to 1.5x4=6.0 under normal temperature conditions (the value given by the poster assumes normal temperature; it may vary under other conditions). However, strictly speaking, the MAWP should also take into account components such as flanges. If a safety relief device is installed as part of the airtightness test and the MAWP is specified as 4.1, but flanges with a rating of 4.0 are used, this seems somewhat contradictory. It makes more sense if the MAWP is changed to 4.0

If the pattern does not specify the maximum allowable operating pressure, then the maximum allowable operating pressure is the design pressure. When the pattern specifies the maximum allowable operating pressure, the selection of the flange still needs to take this maximum allowable operating pressure into account. By definition, the maximum allowable operating pressure is calculated based on the effective thickness of each component, with the minimum value being taken. Therefore, in the case of the original poster, if flanges of PN63 grade are used directly in the design, no calculations are required; whereas if PN40 pipe flanges are used, calculations must be carried out to determine whether they meet the design requirements.