How should the operating pressure be determined on the drawings for liquefied gases and liquefied petroleum gas stored at room temperature?
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This post was last edited by Douwan on 2017-12-13 at 10:39. For a liquefied gas storage tank with thermal insulation, how should the working pressure be specified in the drawings? A friend’s company was undergoing a certification review, and improvement items were suggested regarding this parameter in the drawings. The evaluation expert said: Regardless of the operating temperature, the saturated pressure should always be entered as 50 degrees. Section 3.1.9.3 of the Fixed Volume Code stipulates that the design pressure of pressure vessels for liquefied gases stored at normal temperatures shall be determined based on the operating pressure at the specified temperature. A few words have been added here: “at the operating pressure at the specified temperature.” In my opinion, this operating pressure is not the one indicated on the drawings; rather, it is a value that is artificially added in order to determine the design pressure. Previously, the old regulations used the saturated steam pressure at 50°C as the design pressure, but this was changed later to allow for some flexibility in the design. For example: If a liquid ammonia storage tank operates at actual temperatures ranging from -10°C to 20°C, with an operating pressure not exceeding 1 MPa, should the operating temperature specified on the drawings also be set at 50°C? Should the working pressure also be written as 2.03 MPa? It doesn’t seem right, does it? I have also consulted other experts on this matter; in the past, the values were always filled in based on the actual working pressure and actual working temperature, with the saturated vapor pressure at 50°C being used as a parameter for selecting the design pressure. What do you think about this? A: Regardless of the operating temperature, the saturated pressure should always be entered as 50 degrees ； B: Fill in with the saturation pressure corresponding to the actual operating temperature ；
The design pressure of pressure vessels for storing liquefied gases at room temperature is determined based on the operating pressure at the specified temperature. According to Table 3-1 of the vessel regulations, the critical temperature is taken as 50 degrees; two scenarios are considered: one without insulation measures and the other with such measures. In the case without insulation, the operating pressure is determined using either the saturated steam pressure at 50 degrees or the gas pressure at 50 degrees, depending on the situation, and the design pressure is established on this basis. When heat insulation measures are in place, two scenarios are considered: when there are no experimental measurement temperatures, the critical temperature shall be no less than 50 degrees; based on the saturated vapor pressure at the highest operating temperature that may be reached, and if it is less than 50 degrees, the gas pressure at 50 degrees shall be used. When experimental measured temperatures are available (and these temperatures are below the critical temperature), the saturated vapor pressure at the highest possible operating temperature is used. So, it’s not necessarily the case that the operating temperature is set at 50 degrees.
Since there are no actual experimental data available, we use the saturation steam temperature at 50 degrees or the pressure of gas at 50 degrees as the operating pressure for the liquefied gas. However, according to the capacity regulations, it is not necessarily set at 50 degrees.
So how should we understand \"temperature, together with the corresponding pressure, as load conditions\"?
This post was last edited by zjq1962 on 2017-12-13 at 13:01. Design pressure and design temperature are the conditions that define the basic design loads for a container; they represent the fundamental data for design. Without these two values, it is not possible to carry out the design work.
When temperature and pressure are both used as load conditions, does that mean the two values should correspond to each other? For example, in the case of liquefied gases, there is a saturated vapor pressure associated with the temperature; thus, the operating temperature and operating pressure form a pair of corresponding values. Should they be considered as load conditions together?
For liquefied gases, there is a corresponding relationship between temperature and pressure, but this is not necessarily the case for other substances.
Then you are in contradiction with what you said on the 2nd floor. If it’s convenient, could you take a screenshot of the technical data sheet for the liquefied gas or liquefied petroleum gas storage tanks at your company, so I can study it?
This is the explanation provided in the 2009 version of the regulations. If interpreted based on this text, it seems that the saturated vapor pressure at 50°C should indeed be considered as the operating pressure. But how should the relationship between temperature and pressure be understood?