Issue of non-standard flange thickness at the inlet and outlet of expansion joints
Thread Content
There is currently a double-row large tie-rod type expansion joint, with inlet and outlet flanges that match the pipeline being of DN1000 (HG/T20623-B series). The design pressure is 1.0 Mpa, and the design temperature is 300°C. The cylinder used is of dimensions φ1022.4X12 (outer diameter X wall thickness). Since the flanges of the HG/T20623-B series are of the WN type, the designers opted for non-standard PL type plate flanges; the outer diameter and center circle dimensions were taken from those of the B series. When determining the thickness of the flanges, the SW6 calculation method was used (loose flanges were selected), and the calculated thickness came out to be C=152 mm, while for the WN type flanges of the DN1000-B series, the thickness is C=114.3 mm. It has been observed that when standard pipe flanges and equipment flanges are used in calculations, the SW6 method often yields unsatisfactory results, seemingly due to issues with the calculation model. The question now is: how should the thickness be determined when using non-standard plate flanges? The thickness seems too large. . . Welcome to all experts for discussion and guidance! ! !
Regarding your question, non-standard PL-type plate flanges indeed often require special calculations and design to ensure that they can withstand the specified pressure and temperature conditions. Since the thickness of the WN-type flanges in the DN1000-B series is 114.3 mm, while the thickness of the PL-type flanges calculated by you is 152 mm, which is too thick; this is likely due to the use of the SW6 calculation method and the design being based on loose flanges. First, it is necessary to determine whether the design of the non-standard flange truly requires calculation based on loose flanges, as the design of loose flanges often demands a greater thickness to prevent leakage compared to tight flanges. The following aspects can be considered: 1. **Re-evaluating the flange type**: Based on the actual application environment and requirements, determine whether it is necessary to use PL-type plate flanges, or consider other more suitable flange types, such as continuing to use standard WN-type flanges. 2. **Re-check the calculation model**: If possible, re-verify the calculation model and input parameters. SW6 is typically used for non-standard flange designs, but it is necessary to ensure that all parameters are correct. 3. **Seek expert advice**: Consider consulting engineers or experts specializing in pipeline and fitting design to learn about their experience and recommendations in similar situations. 4. **Conduct experiments or simulation tests**: If conditions permit, experiments or computer simulations can be used to test the pressure-bearing capacity and safety of the designed flanges, to ensure that their performance under actual operating conditions meets the required standards. 5. **Examine the requirements of safety standards and specifications**: Ensure that the thickness and structure of the designed flanges meet the requirements of relevant safety standards and specifications, including pressure resistance and creep resistance. By following these steps, you should be able to more clearly determine the thickness and design of the custom flanges suitable for your expansion joint system. .
It is best to use standard flanges that match those of the pipes. If a non-standard calculation is required, then SW6 or finite element analysis must be used. One should not change the flange design just because it seems that standard flanges might be thinner; the two types of flanges are different and not comparable to each other.
It is advisable to use WN flanges whenever possible, as they result in less stress in the circumferential welds. Using PL flanges leads to stress concentration, which requires thicker material – something that is not cost-effective