VQ35
Mechanical
- Aug 16, 2021
- 7
Is someone able to explain to me if the following is a feature or a bug in Div 2? I am designing a Div 1 vessel and using Appendix 46 for some large nozzle openings.
I made 2 identical nozzles of variable thickness in the same vessel. Same orientation, projection, etc. If I add a relatively thin repad to one of them, the design goes from passing to failing. I went back through the detailed calculations, and the primary contributing factor in the result is the calculation of A2.
Without the repad, the design uses eq. 4.5.28 and 4.5.31 because LH is less than Lx4. 4.5.31 uses the average thickness of the tapered neck ((tn+tnx)/2)as seen in Figure 4.5.13(b).
With the repad, LH now exceeds Lx4, so equations 4.5.29 and 4.5.32 are utilized. However, 4.5.32 uses ONLY the thinner portion of the neck, tn2 in establishing reinforcement area.
If one were just looking at Figure 4.5.13 it would seem that A2c should be greater than A2b if one had identical geometry and a larger LH.
If you are wondering why I bothered adding a repad, it's because the design started as Div 1 but adequate area couldn't be added. The repad carried over when switching calculation method, and I happened to notice that repad thickness has having little effect on the design, but the stress dropped significantly when I removed it.
I made 2 identical nozzles of variable thickness in the same vessel. Same orientation, projection, etc. If I add a relatively thin repad to one of them, the design goes from passing to failing. I went back through the detailed calculations, and the primary contributing factor in the result is the calculation of A2.
Without the repad, the design uses eq. 4.5.28 and 4.5.31 because LH is less than Lx4. 4.5.31 uses the average thickness of the tapered neck ((tn+tnx)/2)as seen in Figure 4.5.13(b).
With the repad, LH now exceeds Lx4, so equations 4.5.29 and 4.5.32 are utilized. However, 4.5.32 uses ONLY the thinner portion of the neck, tn2 in establishing reinforcement area.
If one were just looking at Figure 4.5.13 it would seem that A2c should be greater than A2b if one had identical geometry and a larger LH.
If you are wondering why I bothered adding a repad, it's because the design started as Div 1 but adequate area couldn't be added. The repad carried over when switching calculation method, and I happened to notice that repad thickness has having little effect on the design, but the stress dropped significantly when I removed it.
