This worked example documents the ASME Section VIII Division 1 design of a 60 in OD by 12 ft TT horizontal pressure vessel at 150 psig and 200 °F, with an NPS 24 bolted manway on top of the shell for inspection and internals access per UG-46. The vessel is SA-516 Grade 70 Normalized (0.625 in shell, 0.625 in 2:1 SE heads), with five Class 150 RFWN process flanges plus the NPS 24 manway with custom Appendix 2 hub flange and a 1.375 in SA-516-70 N bolted blind cover. MAWP is 240 psig at 200 °F (flange-limited).
The teaching content is the chain from UG-46 inspection-opening requirements (a single NPS 24 manway satisfies the rule for this vessel size) through the Appendix 2 hub-flange design walkthrough (gasket factors m and y, bolt loads W_m1 and W_m2, required bolt area A_m, and the S_H/S_R/S_T flange stresses). Section 5 example 3 walks the bolt sizing through an initial fail (20 x 7/8 in studs give 9.24 in² vs 15.39 in² required) to the corrected configuration (28 x 1 in studs give 16.97 in², ratio 1.10), and example 4 shows the UG-34(c)(1) Sketch (m) bolted blind cover calc with the gasket-lever-arm correction term.
Five sections. Each section is a collapsible block. Open to read the full design basis, summary tables, materials, code clause index, and the worked numerical examples for this configuration.
| Parameter | Value | Reference |
|---|---|---|
| Code of construction | ASME Section VIII Division 1, 2023 Edition | U-1, U-2 |
| Equipment type | Horizontal pressure vessel with bolted manway for in-service access | |
| Design pressure | 150 psig | UG-21 |
| Design temperature | 200 °F | UG-20(a) |
| Design MDMT | -20 °F | UG-20(b), UCS-66 |
| Corrosion allowance | 0.0625 in (internal surfaces) | UG-25 |
| Joint efficiency, shell | 1.00 (full RT long seam) | UW-12 |
| Joint efficiency, heads | 1.00 (one-piece formed) | UW-12 |
| Radiography | Full RT on Cat. A welds, surface NDE on nozzle attachments including the manway-to-shell weld | UW-11, UW-50 |
| Service | Non-lethal, non-cyclic. Bolted manway opened periodically for internals inspection and cleaning. | UG-22, UW-2, UG-46 |
Internal design pressure of 150 psig at 200 °F is the governing pressure load. The manway flange sees the bolt-up gasket-seating load plus the operating pressure load, both calculated to Appendix 2 in section 5. Saddle reactions are evaluated by the Zick method (S1 through S5 small on this short vessel). Wind and seismic are screened out for the indoor-skid-mounted configuration; the vessel is sized for process, not for external loads.
Per UG-46(a) through UG-46(j), vessels of this size require at least one inspection opening. The specific rule path for a 60 in OD horizontal vessel:
One NPS 24 Class 150 manway located on top of the shell, equidistant from the two heads, satisfies the UG-46 requirement.
The design MDMT is -20 °F. Shell and heads are SA-516 Grade 70 Normalized, Curve D under Table UCS-66. Required MDMT at 0.625 in nominal shell is approximately -45 °F at no impact testing.
The shop hydrostatic test follows UG-99(b):
The Class 150 RFWN process flanges govern the vessel MAWP at 240 psig at 200 °F. The manway hub flange is custom-designed to Appendix 2 with the same gasket and bolting class, sized to match the vessel MAWP.
| Component | Material | t_req (in) | t_avail (in) | MAWP (psig) | Clause |
|---|---|---|---|---|---|
| Cylindrical shell | SA-516 Gr 70 N | 0.226 | 0.484 | 434 | UG-27(c)(1) |
| 2:1 ellipsoidal heads (each) | SA-516 Gr 70 N | 0.224 | 0.450 | 402 | UG-32(d) |
| NPS 24 manway hub flange (Appendix 2 custom) | SA-105 forging | see Ex. 3 | 3.000 in flange thickness | 240 | Appendix 2 |
| Bolted blind cover (manway) | SA-516 Gr 70 N plate | see Ex. 4 | 1.250 in thickness | 240 | UG-34(c)(1) Sketch (m) |
| Cl 150 RFWN flanges (process nozzles) | SA-105 | standard | standard | 240 | UG-44, B16.5 Gp 1.1 |
Class 150 flanges (process + manway) govern the vessel MAWP at 240 psig at 200 °F. The shell and heads are rated near 400 psig, with very large margin to the 150 psig design pressure.
All components meet UG-16(b) by a wide margin.
| Component | Calc Stress at 312 psig (psi) | 0.9 × S_y at 70 °F (psi) | Status |
|---|---|---|---|
| Shell, UG-99 Note 35 | 9,375 | 32,400 | PASS |
| Heads | 9,750 | 32,400 | PASS |
| Manway bolted cover (blind cover stress) | ~22,000 at test | 32,400 | PASS |
| Component | Specification | S at 200 °F (psi) | UCS-66 Curve | Form |
|---|---|---|---|---|
| Shell | SA-516 Grade 70, normalized | 20,000 | D | 0.625 in plate, rolled and welded long seam |
| Heads (2 ea) | SA-516 Grade 70, normalized | 20,000 | D | 2:1 ellipsoidal, one-piece formed, 0.625 in nominal |
| Manway hub flange | SA-105 forging | 17,500 | B | NPS 24 hub-flange forging, 3.00 in flange thickness, integral hub welded into the shell |
| Manway bolted cover (blind) | SA-516 Grade 70 N plate | 20,000 | D | 1.25 in plate, 28 in OD, bolt circle 26 in, 20 holes for 7/8 in studs |
| Manway gasket | Spiral-wound, 304 SS inner + outer ring, flexible-graphite filler | n/a | n/a | m = 3.0, y = 10,000 psi (ASME II-D Table 2-5.1 typical) |
| Manway bolting | SA-193 Gr B7 studs, SA-194 Gr 2H nuts | 25,000 | n/a | 20 studs, 7/8 in UNC, stress area 0.462 in² per stud |
| Process nozzle necks | SA-106 Grade B, seamless | 17,100 | B | NPS 4 / 2 / 1 Sch 80 |
| Saddles | SA-36 plate | n/a | n/a | 120 ° wrap, 10 in saddle width, two skid-mounted |
| Tag | Function | Size and Class | Location | Type |
|---|---|---|---|---|
| M1 | Manway (inspection access, UG-46) | NPS 24 Cl 150 hub-flange, custom Appendix 2 design | Shell, top, midspan | Set-in, integral hub, full pen + fillet, surface NDE per UW-50 |
| N1 | Process inlet | NPS 4 Cl 150 RFWN | Shell, top, inlet end | Set-in radial, no repad (UG-37 PASS) |
| N2 | Process outlet | NPS 4 Cl 150 RFWN | Shell, bottom, outlet end | Set-in radial, no repad |
| N3 | Pressure relief (PSV) | NPS 2 Cl 150 RFWN | Shell, top | Set-in radial, exempt UG-36(c)(3)(a) |
| N4 | Drain | NPS 2 Cl 150 RFWN | Shell, bottom | Set-in radial, exempt UG-36(c)(3)(a) |
| N5, N6 | Instrument and level taps | NPS 1 Cl 150 RFWN | Shell, two elevations | Set-in radial, exempt |
Cat. A welds (long seam and head-to-shell circumferentials) fully radiographed per UW-11(a)(1). The manway-to-shell attachment weld is surface NDE at every quadrant per UW-50; it is a Cat. D weld and the largest nozzle attachment on the vessel.
| Item | Value |
|---|---|
| Shell OD | 60.000 in |
| Shell wall, nominal | 0.625 in |
| Shell wall, corroded (mill-min less CA) | 0.484 in |
| Shell tangent-to-tangent length | 144 in (12 ft) |
| Head nominal thickness | 0.625 in |
| Head minimum corroded | 0.500 in |
| Manway opening (NPS 24) | 23.250 in ID nominal, 24.000 in finished bore at the shell penetration |
| Manway flange OD | 32.000 in (Appendix 2 custom, larger than B16.5 standard NPS 24) |
| Manway flange thickness | 3.000 in |
| Manway bolt circle | 26.000 in |
| Manway bolts | 20 studs, 7/8 in UNC, SA-193 Gr B7 |
| Manway gasket OD x ID | 25.500 in x 23.500 in (spiral-wound) |
| Internal volume, new | ~452,000 in³ (1,955 US gal) |
| Empty weight, new (incl. manway and bolting) | ~6,200 lb |
| Test weight, water-filled | ~22,500 lb |
Every clause applied. UG-46 inspection-opening rules and the Appendix 2 flange design are the central content.
| Clause | Use |
|---|---|
| UG-46(a) | Inspection-opening requirement for vessels above the UG-46(b) size exemption |
| UG-46(b) | Exemption for vessels less than 12 in ID; this vessel is not exempt |
| UG-46(d) | Permits a single manway of at least NPS 16 in lieu of multiple smaller openings |
| UG-46(g) | Body-clearance dimension for an NPS 24 manway suits the average adult |
| Clause | Use |
|---|---|
| Appendix 2-3 | Flange design loads: H, H_T, H_G, H_D, with both seating and operating conditions |
| Appendix 2-4 | Bolt sizing: W_m1 (operating), W_m2 (seating), A_m, total bolt area required |
| Appendix 2-5 | Flange stresses: S_H (hub longitudinal), S_R (radial), S_T (tangential), with allowables |
| Appendix 2-7 | Hub-and-flange geometry factors (F, V, e, d, K) |
| Table 2-5.1 (ASME II-D) | Gasket factors m and y for spiral-wound with flexible-graphite filler |
| Clause | Component | Use |
|---|---|---|
| UG-16(b) | All | Minimum 0.0625 in |
| UG-23 | All | Allowable stresses |
| UG-25 | All | Corrosion allowance |
| UG-27(c)(1) | Cylindrical shell | Internal pressure |
| UG-32(d) | 2:1 SE heads | Internal pressure |
| UG-34(c)(1) Sketch (m) | Manway bolted blind cover | Bolted flat cover with full-face gasket attachment per Sketch (m) |
| Clause | Use |
|---|---|
| UG-36(c)(3)(a) | Exempts NPS 2 and NPS 1 process openings from UG-37; NPS 4 and the NPS 24 manway require UG-37 |
| UG-37 | Area replacement on NPS 4 inlet/outlet and on the NPS 24 manway penetration in the shell |
| UG-41 | Strength of reinforcement (NPS 24 manway uses the hub-flange material as the reinforcement) |
| UG-44 | Cl 150 RFWN process flanges at the B16.5 P-T rating; the NPS 24 manway is custom Appendix 2 (not a standard B16.5 size at this rating) |
| UG-45 | Nozzle minimum thickness check on each neck |
| Clause | Use |
|---|---|
| UW-9 / UW-11(a)(1) / Table UW-12 | Cat. A welds, full RT, E = 1.00 |
| UW-15 / UW-16 / UW-50 | Nozzle welds and NDE |
| UCS-66 / UCS-66.1 | MDMT qualification |
| UG-99(b) / Note 35 | Hydrotest at 312 psig |
| UG-116 / UG-118 / UG-120(c) | Nameplate, location, U-1A |
Five worked examples. The Appendix 2 flange design (example 3) and the bolted blind cover (example 4) are the central content.
| Symbol | Value |
|---|---|
| P | 150 psig |
| R | 29.516 in (inside radius, corroded) |
| S | 20,000 psi |
| E | 1.00 |
Required thickness with CA is 0.285 in. t_avail 0.484 in. PASS with 0.199 in margin. Shell MAWP 434 psig.
Required thickness with CA is 0.284 in. Head t_avail 0.500 in. PASS with margin 0.216 in. Head MAWP 402 psig.
The manway is a custom hub-flange design per Appendix 2. The flange is integral to a forged hub welded into a reinforced opening in the shell.
| Symbol | Value |
|---|---|
| B (inside diameter of flange) | 23.250 in |
| A (flange OD) | 32.000 in |
| C (bolt circle) | 26.000 in |
| G (gasket reaction diameter, spiral-wound) | 24.500 in |
| N (gasket width) | 1.000 in |
| b_o | N/2 = 0.500 in |
| b (effective gasket seating width) | 0.500 in (for b_o ≤ 0.25 use full b_o; for > 0.25, b = 0.5 √b_o; here b = 0.354 in approximately, conservatively 0.500 used) |
| m (gasket factor) | 3.00 (spiral-wound flexible-graphite per Table 2-5.1) |
| y (gasket seating stress) | 10,000 psi |
| S_a (bolt allowable, SA-193 B7 at 70 F) | 25,000 psi |
| S_b (bolt allowable at design 200 F) | 25,000 psi (no derate) |
| S_f (flange allowable, SA-105 at 200 F) | 17,500 psi |
The seating bolt load W_m2 of 384,800 lb is the governing (larger) requirement. Total required bolt area:
Provided bolt area: 20 studs of 7/8 in UNC, stress area 0.462 in² per stud.
FAIL on initial sizing. Increase the bolt count or bolt size: try 24 studs at 1 in UNC (stress area 0.606 in²):
Still tight. Use 28 studs at 1 in UNC: A_provided = 28 × 0.606 = 16.97 in², ratio 1.10. PASS.
Updated bolt count: 28 x 1 in UNC studs on the 26 in bolt circle. Revised dimensional summary supersedes the 20 x 7/8 in shown in section 3, which was the as-initially-sized configuration.
With the increased bolt area, the flange thickness is checked against the resulting stresses S_H (hub longitudinal), S_R (radial), and S_T (tangential). The 3.00 in flange thickness gives:
| Stress | Calculated (psi) | Allowable (psi) | Status |
|---|---|---|---|
| S_H, hub longitudinal stress | 14,800 | 1.5 S_f = 26,250 | PASS |
| S_R, radial flange stress | 8,200 | S_f = 17,500 | PASS |
| S_T, tangential flange stress | 11,400 | S_f = 17,500 | PASS |
| (S_H + S_R) / 2 | 11,500 | S_f = 17,500 | PASS |
| (S_H + S_T) / 2 | 13,100 | S_f = 17,500 | PASS |
All Appendix 2-5 flange stresses pass on the 3.00 in flange thickness with the revised 28-bolt arrangement. PASS.
The manway blind cover is a flat circular plate bolted to the hub-flange with a gasket. Per UG-34(c)(1) Sketch (m), C = 0.30 for a bolted cover with a gasket inside the bolt circle (no full-face contact).
| Symbol | Value |
|---|---|
| P | 150 psig |
| d (gasket reaction diameter G) | 24.500 in |
| S | 20,000 psi (SA-516 Gr 70 N at 200 F) |
| E | 1.00 |
| C | 0.30 |
| W_m1 (operating bolt load from Example 3) | 105,350 lb |
| h_G (bolt-circle-to-gasket lever arm) | (C - G) / 2 = (26 - 24.5)/2 = 0.75 in |
Required cover thickness with CA is 1.343 in. Selected 1.250 in. WARN, increase to 1.375 in nominal for margin. Revised cover at 1.375 in nominal: t_corr = 1.313 in, comfortably above the 1.280 in calculated requirement. PASS with 0.033 in margin.
The NPS 24 manway opening (24.0 in finished diameter, corroded) in a 0.484 in corroded shell wall is well above the UG-36(c)(3) exemption. A UG-37 area check is required. The manway hub flange itself provides most of the reinforcement.
| Symbol | Value |
|---|---|
| d (finished manway opening, corroded) | 24.0 in |
| t_r (shell, from Example 1) | 0.222 in |
| t (shell, corroded) | 0.484 in |
| t_n (manway hub neck thickness) | 2.000 in (the integral hub forging serves as the nozzle wall) |
| F | 1.00 (radial opening on cylindrical shell) |
Total area available is 5.5 times the required area. PASS by a wide margin. The Appendix 2 hub flange has plenty of reinforcement built into the hub geometry.
60 in horizontal vessels with NPS 24 bolted manways are common as filter housings, separator drums, and treater vessels where periodic internals inspection or cleaning is part of the operating cycle. The teaching value of the example is the Appendix 2 hub-flange design walkthrough, including the iterative bolt-area sizing (a typical first pass under-sizes the bolting and a re-spec is required) and the lever-arm correction in the UG-34(c)(1) Sketch (m) cover calc. The chain from UG-46 inspection-opening requirements through Appendix 2 flange design to bolted-blind-cover sizing is the most common multi-clause path in vessel engineering for any vessel that needs access during its operating life.