Summary of Classic SW6 Computational Problems

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1. For equipment flanges conforming to NB/T4707, when should Type A or Type B studs be used? Answer: Type B studs should be used when the operating temperature is greater than 250°C; otherwise, Type A studs should be used. The purpose is to reduce bolt stiffness, which helps to lower the temperature differential stress on the studs. Generally speaking, in cases where the loading conditions are severe, it is best to choose type B. The reasons are: (1) Using a thinner shaft can reduce the stiffness of the bolt, thereby decreasing the temperature difference load between the bolt and the flange and improving the stress conditions on the flange. In bolt-flange connection structures, when there is a temperature difference between the bolt and the flange, thermal deformation differences occur between them. This poor thermal deformation leads to temperature difference stress between the bolt and the flange. The magnitude of this temperature difference stress depends on the temperature difference between them as well as the material; in other words, once the temperature difference and the material are determined, the magnitude of the temperature difference stress is also determined. And the corresponding total temperature difference load is equal to the product of the temperature difference stress and the cross-sectional area of the bolt. If the bolt cross-sectional area can be kept as small as possible while still meeting the connection strength requirements, the total temperature difference load acting between the bolt and the flange can be reduced, thereby improving the stress conditions on the flange. (2) The diameter of the smooth shaft portion in a Type B bolt is equal to the root diameter of its threads, and a small radius serves as a transition between this smooth portion and the threads; as a result, the overall structural continuity is good. Therefore, compared to Type A bolts, it has a greater capacity to withstand alternating loads. (3) Flange bolts are often not subjected only to tensile forces; during use they are also frequently exposed to bending, torsion, and impact forces. Overloading can easily occur during tightening, so a higher safety factor is generally required for such bolts. This can be seen from the comparison between Tables 1 and 2 in GB/T150.1-2011. 2. Explanation of the relief holes in high-pressure multi-layer containers: First, it is necessary to understand the function of these relief holes. Their main purposes are: (1) to serve as a warning system; if there is a leak in the inner container, fluid can leak out through these relief holes layer by layer, allowing the problem to be detected as early as possible. (2) It serves as an exhaust hole, similar to those on the reinforcement rings and support shims; therefore, it is a through-hole. The exhaust here does not refer to the gas generated when the laminates are butted together. The gas from the lap joint welding can be vented from both ends of the tube section as well as from the unfused areas. The exhaust mentioned here refers to the gas that is needed for the pre-treatment of cracks in the circumferential weld areas at both ends of the tube section, as well as the gases that may be generated during the welding of the tube sections together, with the end flanges, and the end caps. For Class B welds of multi-layer wrapped tube sections, the weld groove requires 6 to 8 millimeters of deposited metal for welding. The thermally expanded gas generated during welding needs to be released. (3) Location of the vent hole. Vent holes are generally provided at both ends of the wrapping cylinder. The position of the hole is 100–150 millimeters away from the inner cylinder of the tube section (depending on the thickness of the cylinder), with a diameter of 6–10 millimeters. Four signal holes are arranged at positions 90 degrees apart in the circumferential direction at each end of the cylinder. The first and second layers are pre-drilled, while the remaining ones are drilled using a flat-bottomed drill after all the layer boards have been wrapped up. The hole depth has reached the limit of the second layer of laminate. 3. When calculating the saddle, does the saddle height h refer to the standard height of the saddle or the height of its web? Answer: Since h is used to calculate the average stress σ9 of the saddle web, the minimum height at the middle of the saddle web should be entered. 4. In GB/T151, a minimum thickness is specified for the cylinder body, but sometimes strength calculations do not require such a thick wall, which seems wasteful, especially for expensive non-ferrous metal equipment. Answer: The minimum thickness specified in GB/T151 takes into account the weight of internal components such as tube bundles, in order to ensure the stiffness required of the cylinder during manufacturing and installation, which is a requirement that must be met. However, for non-ferrous metal equipment, GB/T151 does not specify a minimum thickness for the cylinder; please refer to the relevant referenced standards when designing. 5. When calculating fixed-tube-sheet heat exchangers, if Φ19×2 tubes are used, the stress check for these tubes often fails, as the allowable stress calculated is very low. What methods can be used to make adjustments? Answer: First of all, please note whether the equivalent value for pressure-induced instability of the pipe is taken in accordance with the provisions of GB/T151; this value has a significant impact on the allowable stress of the pipe. Secondly, the diameter of the pipe also has a significant impact on the allowable compressive stress; generally, a pipe with a diameter of Φ25 has an allowable compressive stress that is about 50% higher than that of a pipe with a diameter of Φ19. Since the diameter of the tubes generally cannot be changed as it has a significant impact on the heat exchange area, in practice, the only option is to reduce the spacing between the baffle plates. 6. The flange gasket uses an “O” ring – which type of sealing surface should be used for calculation? How should the m and y values be chosen? Answer: For \"O\"-ring gaskets, the basic sealing width is calculated as bo = N/2 (where N is the width of the \"O\" ring), and the values for m and y are selected based on synthetic rubber as specified in Table 7-2 of GB/T150, according to the Shore hardness. 7. How to calculate the inner cylinder of a container with a semi-jacket? Answer: In engineering terms, it can be calculated using a full jacket design, which yields a more conservative result. 8. When designing the external pressure of the inner cylinder of a jacketed vessel, should the design external pressure be based on the design pressure or the test pressure of the jacket? Answer: According to GB/T150, the design pressure of the jacket should generally be used for designing the external pressure on the inner cylinder. If the calculated allowable external pressure on the inner cylinder is lower than the test pressure of the jacket, it is necessary to indicate this in the calculation documents and drawings, specifying the pressure that should be maintained on the inner cylinder during the jacket pressure test. This treatment allows for the full utilization of the material; SW6 is also treated in this way. However, if it is difficult to maintain pressure in the inner cylinder during the jacket pressure test, the external pressure of the inner cylinder must be designed using the test pressure of the jacket. 9. The cyclone separator has an inclined pipe, and it is a large-sized pipe – what method should be used for calculation? Answer: Since the pressure area method can only be used for the stress analysis of openings in radially large nozzles, inclined large nozzles cannot be analyzed using this method; instead, finite element programs must be employed. 10. There is a storage tank containing solids under pressure, and it meets the structural requirements specified in the standards for towers. Can it be calculated as a tower? Answer: Yes. For more industry news, please add WeChat sjytangtang