What is the overpressure limit

The following content is from the Internet: [GB-150] Steel pressure vessels... B4.2 Pressure limits for vessels and operating pressure of relief devices. B4.2.1 When a relief device is installed on a vessel, its operating pressure shall not exceed the design pressure, and the pressure limit for that vessel shall not be more than 10% of the design pressure or 20 KPA, whichever is greater. B4.2.2 When multiple relief devices are installed on a container, the operating pressure of one of these relief devices shall not exceed the design pressure; the operating pressure of the other relief devices may be increased, but it must not exceed 4% of the design pressure. The overpressure limit for this space shall not exceed 12% of the design pressure, or the greater of the two values, 30 KPA. B4.2.3 When a vessel may be exposed to fire or approach an unpredictable external heat source that could pose a danger, auxiliary relief devices shall be installed to ensure that the excess pressure inside the vessel does not exceed 16% of the design pressure. 1. As can be seen from above, GB-150 here is basically based on the corresponding provisions of ASME VIII. It is worth noting that when a vessel is equipped with multiple relief devices, the overpressure limits for the vessel are specified for non-fire and fire conditions: GB-150 specifies 12%/16%, while ASME specifies 16%/21%. (Privately speculated, it may be that the standard compilers took into account factors such as China’s steel production processes, container manufacturing techniques, and quality control systems, which led to relatively low limits set for container overpressure.) ) 2. If a container is equipped with only a single safety valve, for normal non-fire conditions of the container, the overpressure limit is 10% according to both GB-150 and ASME. For fire conditions, ASME specifies a pressure excess limit of 21% (whether for a single valve or multiple valves). ), GB-150 does not address this aspect, but in my opinion, a superpressure limit of 16% should be applied. 3. Whether it is GB-150 or ASME VIII, for a single safety valve used to protect a pressure vessel, it is undoubtedly necessary that the set pressure of the safety valve be less than or equal to the vessel’s MAWP, regardless of whether the valve is operating under normal conditions or in fire conditions. 4. For pressure vessels protected by multiple safety valves, the set pressure of the first safety valve should be less than or equal to MAWP, while the set pressure of the second safety valve should be less than or equal to 4% (GB-150)/5% (ASME VIII) under non-fire conditions. In fire conditions, the set pressure of the second safety valve should be less than or equal to 5% (GB-150)/10% (ASME VIII).

According to my understanding: the overpressure limit = the discharge pressure of the safety valve – the design pressure of the container

Well, I really can’t understand this concept either; I came here looking for answers. After reading what was said on the 2nd and 3rd floors, I feel like I understand a bit about daily-use chemicals, but I’m still a bit confused. Sigh

Definition of 150 P22 pf – the discharge pressure (absolute pressure) of the relief device, consisting of the design pressure and the overpressure limit, in MPa.

The first sentence of B3.1 explains it. Use the design pressure of the container as the starting pressure for the overpressure limit.

The overpressure limit is a range; the minimum value is the setting pressure of the safety valve, while the maximum value varies depending on the number of safety valves (refer to B3.2)

Is it necessary to calculate the overpressure limit, or is it sufficient to use 10% of the design pressure for a single relief device, or 16% for multiple relief devices?