Every hole cut in a pressure vessel takes away metal that was carrying the hoop stress. This lab shows how ASME Section VIII Division 1 puts it back. Choose a nozzle, a schedule and a reinforcing pad, then watch the UG-45 neck check and the UG-37 area-replacement balance update in 3-D and in section.
| A, area to replace · d·tr + 2·tn·tr·(1−fr1) | |
| A1, excess in shell | |
| A2, excess in nozzle neck | |
| A41 + A42, fillet welds | |
| A5, reinforcing pad | |
| Total available |
How to use the lab
- Start from V-100’s 12-inch nozzle: SCH 60 neck, 450 × 16 mm pad, 15 barg. Press Reset to V-100 any time.
- Drop the schedule to XS or STD and watch UG-45 fail: the neck is too thin before reinforcement is even considered.
- Untick the pad to see that the shell, neck and weld alone give only about half of the required area.
- Press Size pad to minimum to get the smallest pad (rounded up to 50 mm) that balances UG-37. Try a thinner pad, or a smaller nozzle, and see how the answer changes.
The worked result for V-100
| Check (V-100 N1, NPS 12 at 15 barg) | Result |
|---|---|
| UG-45 neck, required | 11.33 mm (min of shell tb1 12.88 and std-wall tb3 11.33) |
| STD / XS / SCH 60 at 87.5 % | 8.34 ✗ / 11.11 ✗ / 12.49 ✓ |
| A, area to replace | 3,009 mm² (d = 301.31 mm corroded, tr = 9.88 mm) |
| Shell + neck + weld, no pad | 930 + 450 + 86 = 1,466 mm² (49 %), so a pad is needed |
| Minimum pad OD at 16 mm | 405.4 mm, ordered as 450 × 16 mm |
| With the 450 × 16 pad | 930 + 519 + 86 + 169 + 2,018 = 3,722 mm² (+24 %) |
A note on A2 with a pad. Without a pad, the neck’s credit is A2 = min[5(tn−trn)·fr2·t, 5(tn−trn)·fr2·tn] = 450 mm². With a pad, Fig. UG-37.1 lets the second term grow with the pad, A2 = min[5(tn−trn)·fr2·t, 2(tn−trn)(2.5tn+te)·fr2] = 519 mm², and the lab uses that. Video Part 4 kept the no-pad value, which is conservative: it gives a 409.8 mm minimum pad instead of 405.4 mm, and the same 450 mm pad either way.
Learn the method
Watch the full calculation in Pressure Vessel Design Part 4: nozzle reinforcement, UG-45 and UG-37. The same V-100 vessel runs through the whole Pressure Vessel Design course, which starts with 5 free lessons. The shell used here is sized in the Pressure Vessel Shell Lab and the UG-27 worked example. More tools: all Design Hub Labs · free calculators.
Teaching model, not a design tool. It covers radial nozzles under internal pressure only. It doesn’t cover hillside or tangential nozzles, external pressure (UG-37(d)), or nozzles in a weld seam. Weld strength paths (UG-41) are not checked. Final design follows your project specification and code edition.
