Issues regarding the calculation conditions for safety valves on fully filled containers
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In API521, the calculations regarding fully filled containers are covered in the section on hydraulic expansion; it is noted that this applies only when the fully filled container is exposed to sunlight, and reference should be made to item c) in section 4.4.12.1 of API521. But if a full-liquid container is affected by a fire, is the heat absorbed calculated based on the fire conditions, while the actual amount of liquid released is calculated based on the volume of liquid discharged, with the discharge volume determined using the hydroexpansion formula in Chapter 4.4.12? Additionally, should the requirements regarding steam generation under fire conditions also be taken into account? Should the safety valve be verified based on the released steam, or calculated accordingly? (Refer to the last paragraph in section 4.4.12.3) I would appreciate it if the experts at Haichuan could help answer this question. Thank you!
Facing the same problem, I hope some expert can provide an answer :)
Let’s consider them in order: first, the liquid expands, and then it vaporizes. It seems that both processes need to be taken into account; either the larger value should be used, or both values. There is one prerequisite: it depends on what kind of liquid it is. For substances that vaporize very easily, vaporization should be considered directly
Fire and thermal expansion are two different conditions; in principle, fire causes thermal expansion, and in principle both conditions should be taken into account in the calculations. However, PAI also analyzes the situation during a fire: initially, heat transfer caused by the fire leads to expansion of the liquid first; once a constant pressure is reached, the safety valve opens, and at this point the discharge is usually in a gas-liquid mixture form. Then, once a certain gas phase space is established inside the container, the release process becomes equivalent to the gas phase release calculation used in regular fire calculations. The key issue is the nozzle area required for the initial release of the gas-liquid phase, which is usually much smaller than that needed for the release of a pure gas phase during a fire. Therefore, for fire conditions with a completely liquid phase, there is no need to account for thermal expansion.
I can’t remember; is it better to have the safety valves for liquids and gases separate? In the case of a full-liquid container, does “full liquid” refer to the maximum liquid level or to the gas space within the container? If the container has a gas phase space, assuming that the liquid’s expansion coefficient is not very high, that is, by calculating based on the release of gas during a fire, I am in favor of the calculation method proposed by the person above~
I agree with you, thank you! To summarize: 1: For full-liquid containers, if thermal expansion is taken into account, the safety valve is calculated using the thermal expansion formula. 2: For full-liquid containers, in the event of a fire, the safety valve does not need to account for the expansion and release of liquid; instead, it only needs to consider the release of gas generated by the vaporization of the liquid. The calculation for such safety valves is based on gas release. I wonder if other fans have different opinions.