Jacketed vessel design (inner cylinder at atmospheric pressure, jacket at 0.4 MPa positive pressure)
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Recently, I was tasked with designing a batch of jacketed vessels (with the inner cylinder at atmospheric pressure and the jacket at a pressure of 0.4 MPa). As this was my first time carrying out such design work, I consulted numerous standards and spent a lot of time on forums to develop a preliminary draft for discussion among colleagues; please point out any shortcomings. Design parameters: Inside the container (material 321, diameter 2800): Medium: sodium sulfate, lithium hydroxide solution; Density: 1200 kg/m3; Operating pressure: atmospheric pressure; Operating temperature: -3 to -6°C. Inside the jacket (material Q245R, diameter 3000): Medium: ethylene glycol; Operating pressure: 0.4 MPa; Operating temperature: -10°C. Details of the pipe connections are provided in the attachments. Design process: 1. Selection of design pressure and design temperature – The design pressure and design temperature for the jacket are determined in accordance with the HG/T20580-2011 standard; the pressure is 0.4*1.05=0.42 MPa ； Select the lowest operating temperature of -10 ； The design pressure for the inner cylinder is set at atmospheric pressure, while the design temperature is set at the lowest operating temperature of -6 ； 2. Inner cylinder design: The designed pressure for the inner cylinder is at atmospheric pressure, but it is subjected to external pressure during operation. Since it is not possible to perform calculations with a value of 0 at the designed pressure for SW6, a value of 0.001 MPa is used as the designed pressure for the inner cylinder. When calculating cylinders in SW6, it is necessary to enter the calculation length of the cylinder under external pressure, which is calculated according to 4.3 e) of GB150.3-2011 (with stiffening rings provided). Questions in this regard: (1) If no reinforcing ring is designed, SW6 calculations indicate that pressure retention in the inner cylinder is required; however, since the top of the inner cylinder is a flat cover head, a thick steel plate is needed for the head even at low pressure levels, which is why a reinforcing ring is installed. To increase the safety factor, two rings of reinforcement are designed inside the inner cylinder; these reinforcement rings divide the inner cylinder (together with the depth of the lower head’s curved surface) into roughly three sections. The largest value of L1 (as shown in the figure) is chosen as the calculation length for the cylinder under external pressure. Is this a reasonable approach? ? (2) When entering the reinforcement ring value in SW6, it is required to input “half of the sum of the calculated lengths of the cylinders on both sides of that reinforcement ring”. To understand this value, one calculates half of the sum of the calculated lengths on each side centered on a single reinforcement ring, namely (l1+l2)/2 and (l3+l2)/2), and then selects the larger value. Is this correct? 3. Head design: A flat cover head is used for the upper head; since mixing equipment is installed at the upper part, a conservative wall thickness is chosen, consistent with that of the cylinder ； The lower head design also takes into account the effect of negative pressure; meanwhile, in SW6 the nominal thickness of the head should be set to the minimum thickness achievable during manufacturing, with a negative deviation specified as 0. The minimum thickness of the head is calculated as: δmin = δn – C1 – (δn – C1) * reduction percentage, where C1 represents the negative thickness deviation, typically 0.3 ； The thinning rate is specified in the head standard GB/T 25198-2010. In addition to the minimum forming thickness, attention must be paid to selecting a welding joint coefficient that is compatible with the equipment; furthermore, 100% radiographic testing and 100% penetrant testing are required (magnetic particle testing cannot be used for austenitic materials). 4. The jacket cylinder: the static pressure of the liquid must be taken into consideration. 5. Selection of the manhole for the inner cylinder: Since the inner cylinder is a vessel under normal pressure, the manhole is located at the top and is not subject to pressure; however, as the medium inside the inner cylinder is highly alkaline, a manhole with a slightly higher pressure rating is chosen to prevent leaks. Dear sea friends, please engage in active discussions and offer your guidance!
The inner cylinder is at atmospheric pressure, while the jacket is at 0.4 MPa; therefore, the maximum pressure difference should be taken into account during calculations. The calculated pressure for the inner cylinder should be -0.4 MPa – why is 0 used instead?
Paragraph 4.3.3(e) of GB150.1-2011 stipulates that jacketed vessels shall have their design pressures determined separately, with the calculation pressure being based on the maximum pressure difference. The design pressure is set at atmospheric pressure, and the calculated pressure SW6 will be taken into account automatically.
SW6 requires the input to be the design pressure; it will set the calculated pressure at -0.4. The original poster’s approach is quite clear
After taking a look, it seems there are quite a few issues. I’d like to share my opinions in an effort to stimulate discussion and see how others think about it. 1. Design parameters: The design temperature should take into account not only low temperatures but also the high temperatures that may be reached. It is necessary to consider, from the perspective of the process system, whether temperature fluctuations could result in levels lower or higher than the operating temperature, and the most extreme conditions must be considered. Similarly, the design pressure is not simply a result of multiplying by 1.05; it also needs to be considered from the perspective of the system. 2. Inner cylinder design: Since this device appears to have a mixing function, it is advisable to avoid using internal or external pressure reinforcement rings, as these may affect the mixing efficiency of the materials inside. Moreover, the temperature and pressure are not high; since the diameter is larger, I think it’s better to treat it as having no reinforcing ring. Note that when calculating the length under external pressure, the height of the head should be taken into account. I don’t understand what you mean by the internal pressure needing to be maintained Has the thickness already been determined, and is it because the external pressure is not sufficient that pressure holding is required? Just increase the thickness then. 3. Head design: Personally, I don’t think 100% penetrant testing is necessary; RT is sufficient, and a 100% RT test with grade III being acceptable is enough. There are many issues with the upper head; it is a flat cover that does not bear pressure. However, due to the need for a mixer and the requirements related to its own stiffness, it is necessary to consider installing beams. If you want to do the calculation, there are methods available for containers under normal pressure; if you don’t want to calculate, 6 to 8 millimeters should be sufficient. However, the beams must be taken into consideration, and if the beams are not considered, an agitator will also be needed, in which case the required thickness will be much larger. 4. Clamp sleeve body: I don’t understand what you mean; why not calculate it based on the internal design pressure? 5. Manhole: Since the pressure at the top is at normal levels and the medium in question doesn’t seem to be volatile or hazardous, I think a manhole designed for normal pressure would be sufficient; there’s no major issue with upgrading it to a higher standard either.
Thank you to this sea friend. 1. There is only limited data available regarding the design pressure and design temperature; although the system was taken into consideration, the client did not provide it； 2. The concept of maintaining pressure in the design of the inner cylinder means that during the hydraulic testing of the jacket, the inner cylinder cannot withstand such high pressures; therefore, reinforcing rings are installed. When designing these reinforcing rings, cost is a key consideration – adding 2 mm of steel plate will result in an additional weight of one ton, costing nearly 20,000 yuan ； 3. 100% penetration testing of the head is the surface inspection specified in 150 ； 4. The jacket requires consideration of the hydrostatic pressure of the liquid ； 5. Agree
1. If the owner does not provide them, the owner needs to confirm the design parameters; otherwise, there may be subsequent problems. 2. It is necessary to determine whether the reinforcement ring has an impact on mixing; otherwise, it will be a problem if the mixing effect is poor. 3. I don’t quite understand this rule regarding surface inspection of 150 – where was it specified? Is yours greater than 20mm? If it exceeds that limit, wouldn’t not only the head but also the surface need to be inspected? 4. The hydrostatic pressure of this liquid column is quite interesting. Normally, if the equipment isn’t very tall, people might not bother to pay attention to it, but since the pressure here is low anyway, it must be taken into account when performing hydraulic tests on the inner cylinder. It can also be considered in the calculations related to the jacket, but strictly speaking, the density of ethylene glycol is much lower than that of water.
For the inner cylinder, if a pressure of -0.4 MPa is applied directly, wouldn’t it then be classified as a pressure vessel under external pressure? The first time I saw 0.001 entered
Regarding study*, I don’t have any comments to offer to the original poster.
It is to have the owner confirm, with the owner providing the design condition sheet. The reinforcing ring is also there to save costs. Regarding surface inspection, it is specified in Gb150.4—2011 on surface inspection; welded end caps require surface inspection. I hadn’t paid much attention to the fact that anything greater than 20 mm requires testing; it’s probably a requirement related to the materials, not part of the design specifications. I’ll check it tomorrow. Isn’t the hydrostatic pressure of the liquid column something that needs to be taken into account in all cases? Except for 5% less than the design pressure.
Because when using sw6 for calculation, entering 0.001 also results in a value that takes negative pressure into account. So let’s just leave it at that; I think entering -0.4 would work as well, but the hydrostatic pressure of the liquid column needs to be taken into account in advance.