Questions regarding the \"Code for Safe Design of Spherical Storage Tanks for Liquefied Hydrocarbons\" SH3136-2003
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In Section 5 of this specification, 5.1 Temperature: The liquid-filled spherical storage tank shall be equipped with local and remote temperature sensors, ensuring that the temperature of the liquid phase can be measured at the lowest liquid level, as well as facilitating observation and maintenance. 5.2 Pressure: Local and remote pressure gauges should be installed at the upper part of the liquefied gas spherical tank body, along with a separate alarm for high pressure levels. No accessories or connections for other purposes shall be connected between the pressure gauges and the spherical tank. Question: 1. Why does this standard insist on having pressure gauges and thermometers on the spherical tank itself? Is it not possible to install them near the sphere tank at the upper and lower outlet pipes of the sphere tank? 2. What is the high-pressure alarm limit, and how is it defined? 3. If both the temperature and pressure gauges are located at openings on the tank body itself, does this conflict with the requirement of this specification to \"minimize the number of openings on liquefied hydrocarbon spheres\"? Those of you who have experience with atmospheric pressure storage tanks, please share your insights.
1. It is necessary to install pressure gauges and thermometers on the sphere tank itself, as the pressure and temperature at the pipelines connected to the tank do not reflect those of the tank body itself. Moreover, since root valves are present on the tank, the accessories installed on the pipelines may fail to function if the root valves are closed. 2. The high-pressure limit alarm should be determined based on the properties of your material, the storage conditions, and the design pressure of the spherical tank. For example, the design temperature for an acrylic sphere tank is 50 degrees, with a pressure of 2.16 MPa; under normal conditions this pressure is kept below 1.3 MPa, and an alarm can be set when it drops to 1.2 MPa. 3. The temperature gauge has little to do with the number of openings; however, the pressure gauge only needs to be installed at the top of the tank, and an opening can be created to connect a tee, thereby allowing measurement of both the remote and on-site pressures. The above are the issues I encountered during the design process; I hope it will be helpful to you.
What we see most recently is that both the pressure gauge and temperature gauge are located at openings on the inlet pipeline, between the emergency shut-off valve and the spherical tank; this way, even if the valve is closed, it does not affect the ability to read the pressure and temperature. Our high-pressure alarm threshold is 1.65 MPa. This is generally a value specified for laboratory testing. Now, openings are generally only provided on the top and bottom of the tank, with no openings elsewhere.
It’s great stuff. I’d like to ask everyone how to calculate the minimum liquid level in a spherical tank. . . . . . . .
The pressure gauge must be installed on the top of the tank; the gas-phase pressure is determined by the pressure gauge on the tank top, and this value is transmitted to the control room. For remote temperature measurement, it is necessary to take readings at the opening of the tank. If a bimetallic type sensor is used on-site, it can be installed on the inlet and outlet pipelines for easy inspection; however, in this case, the root valve must be a manual valve that remains open, and it should be installed between the root valve and the quick-cut valve.
I share the same idea as the one on the 5th floor, but doing that would mean creating an opening in the actual tank body, which goes against the regulatory requirements; so I’m a bit hesitant.
Ensure that the spherical tank is not emptied within 15 minutes
1. The pressure gauges and thermometers on the spherical tank itself are, as the name suggests, used to monitor the pressure and temperature of the tank’s interior. Among them, high and low pressure alarms as well as high and low interlocks will definitely be available. The key temperature monitoring points are the low vaporization temperature when the spherical tank is first filled with liquid, and the high temperatures in summer. 2. For high-pressure alarms, the maximum pressure under the influence of local temperature is generally taken into consideration; for example, in the case of propylene, we set it at 1.4 MPa. 3. Reducing the number of openings as much as possible does not mean eliminating all openings altogether. At the bottom of a liquefied gas tank, there are usually inlet and outlet lines, lines for waste discharge, temperature transmission systems, flare lines on the tank top, vapor balance lines, pressure transmission systems, liquid level detection systems (servo and radar types), as well as local pressure gauges. In principle, local pressure gauges and pressure transmission systems require separate openings.