Some minor comments on the regulations regarding the operating pressure of liquefied gases stored at room temperature, as shown in Table 3-1.

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This post was last edited by Douwan on 2018-10-16 at 08:49. Everyone is surely familiar with clause 3.1.9.3 of TSG 21-2016, the new regulations regarding the design pressure of pressure vessels for storing liquefied gases at normal temperatures. Below is a screenshot of that clause: It’s a simple table, but it contains quite a lot of information. Here’s the question: 1. When storing XXX at room temperature, does this regulation apply only to the \"storage containers\"? For example, the operating pressure of liquid ammonia storage tanks can be selected from this table, but cannot the operating pressure of tanks used for separating gaseous and liquid ammonia be selected from this table? If analyzed in this way, the liquid ammonia storage tank connected to the separator belongs to the same system, yet there are significant differences in operating pressure and design pressure; doesn’t this also seem unreasonable from a personal perspective? Another example: for an ammonia storage tank that is liquefied at a low temperature of -33°C, with operating pressure at atmospheric pressure, if the specifications state a design temperature of -35°C/-20°C and a design pressure of 0.09 MPa, wouldn’t that mean it is exempt from the regulations governing pressure vessels? Undoubtedly, doing so is wrong; by the same logic, even when a liquid ammonia tank is replaced with a separation tank, selection must still be made according to this table. This regulation regarding tolerance limits has led to many misunderstandings; does storing at room temperature necessarily refer to the storage container? Not at all. Storing at room temperature does not necessarily mean in a storage container. As long as there is a function of storage, it is called storage; the \"separators\" listed above also have a storage function, so this applies to them as well. The origin of this regulation can be traced back to the 1998 version of the safety regulations. In that original version, it specified the design pressure for fixed pressure vessels used to hold liquefied gases; starting with the 2009 version, this was changed to refer to storage at normal temperatures, and the selection criterion for design pressure was altered to use the operating pressure instead. Personally, I think the 98 version’s “formal storage” is more down-to-earth and easier to understand, while the revised “storage at room temperature” is confusing. 2. On the left side of the table, it is “Critical Temperature of Liquefied Gases”, not “Liquefaction Temperature”. The liquefaction temperature is easy to understand: it refers to the temperature at which a substance liquefies under standard conditions. The critical temperature of a liquefied gas is the temperature at which, as the temperature of the liquefied gas rises, its saturated vapor pressure continues to increase. Once the temperature reaches this certain value, further increases in temperature do not result in an increase in the saturated vapor pressure; this temperature is known as the critical temperature. Taking ammonia as another example, the critical temperature of ammonia in its liquefied state is 132.4°C, while the liquefaction temperature under standard conditions is -33°C. Therefore, when selecting tables, be sure not to get the table headers wrong, otherwise it will lead to errors in the basic design data. 3. It is crucial to have insulation or not. It is relatively easy to determine when the equipment lacks insulation; if the critical temperature of the liquefied gas is ≥50°C, the saturated vapor pressure at 50°C shall be used as the operating pressure. Incidentally, a small question: I have always been puzzled by the saturated vapor pressure of liquid ammonia at 50°C. I have checked multiple data sheets regarding liquid ammonia, and the value is 2.03 MPa(a); in some cases it is 2.006 MPa(a). These values are all absolute pressures, not gauge pressures. As for the value of 2.16 MPa given in the old specification, I wonder where it comes from? There are cooling facilities; trouble arises as it’s necessary to check whether there are actual measured temperatures from tests. Regarding this right-side range of the table, “Actual test temperature,” I’ll just say: I believe you. The saturated vapor pressure at the highest operating temperature that can be achieved. Since it’s “possible” to achieve it, then tell me what the difference is between having a “measured temperature” and not having one Therefore, with the updates to standards and regulations, as well as increased enforcement measures, the recommended provisions have been changed ； More and more requirements that were originally stipulated by regulations and standards are now determined by design specifications ； More and more originally clear regulations have become ambiguous, with some provisions even giving rise to ongoing disputes within the industry. So, this pot used to be **carried by others, but now there is a gradual shift towards a design-oriented approach, that is: whoever designs it is responsible for it. The responsibilities of designers are increasing, yet their salaries are decreasing. Sigh. I’m off-topic. Received.