This worked example documents the ASME Section VIII Division 1 design of a 60 in OD vertical pressure vessel at 400 psig and 100 °F, with a 2:1 SE head as the as-built closure at both ends. The vessel uses an SA-516 Grade 70 Normalized shell (1.000 in nominal) and one-piece formed heads (0.875 in nominal), four Class 300 RFWN flange connections, and skid lugs at the lower head transition. The published MAWP is 496 psig, set by the 2:1 SE heads.
The teaching content is the four-way head-type comparison in section 5. The same 60 in OD shell at the same 400 psig design point is closed by each of hemispherical (UG-32(f)), 2:1 ellipsoidal (UG-32(d)), F&D torispherical (UG-32(c)), and welded flat cover (UG-34(c)(2) Sketch (h)) configurations, with required thickness, MAWP at the available thickness, inside head depth, and head weight tabulated side by side. The summary table at the end of section 5 captures the trade-offs at a glance.
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 | Vertical pressure vessel | |
| Design pressure | 400 psig | UG-21 |
| Design temperature | 100 °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 welds | UW-11, UW-50 |
| Service | Non-lethal, non-cyclic, gas or liquid (not specified) | UG-22, UW-2 |
Internal design pressure of 400 psig at 100 °F is the governing load. Weight, wind, and seismic are screened out for the skid-mounted indoor-or-sheltered configuration. The vessel is non-cyclic per UG-22(e) screening.
The Minimum Design Metal Temperature is -20 °F at the full design pressure of 400 psig. The shell and the heads are SA-516 Grade 70 Normalized, Curve D under Table UCS-66. Required MDMT at the shell thickness (1.000 in nominal) is approximately -35 °F at no impact testing.
The shop hydrostatic test follows UG-99(b):
SA-516 Grade 70 does not derate below 300 °F so the LSR is 1.00. The Class 300 RFWN flanges have a cold rating of 770 psig at 70 °F, well above the test pressure.
The as-built closure for this vessel is 2:1 SE heads at both ends. The teaching content of the page is the side-by-side head-type comparison in section 5: hemispherical, 2:1 SE, F&D torispherical, and welded flat cover, each sized to a MAWP that meets or exceeds the 400 psig design pressure on the same 60 in OD shell. The comparison shows how head choice trades thickness against vessel height, weight, and fabricated cost.
| Component | Material | t_req (in) | t_avail (in) | MAWP (psig) | Clause |
|---|---|---|---|---|---|
| Cylindrical shell | SA-516 Gr 70 N | 0.591 | 0.813 | 548 | UG-27(c)(1) |
| Top and bottom 2:1 SE heads | SA-516 Gr 70 N | 0.585 | 0.725 | 496 | UG-32(d) |
| Cl 300 RFWN flanges (4) | SA-105 | standard | standard | 750 | UG-44, B16.5 Gp 1.1 |
| NPS 6 inlet nozzle neck | SA-106 Gr B | 0.030 | 0.376 | matches shell | UG-27(c)(1), UG-45 |
The 2:1 SE heads govern the vessel MAWP at 496 psig. The shell at 548 psig and the Class 300 flanges at 720 psig at 100 °F both sit above the head capacity. Section 5 compares the four common head types on this same shell and shows how each head choice shifts the governing component.
All components meet UG-16(b) by a wide margin.
| Component | Calc Stress at 645 psig (psi) | 0.9 × S_y at 70 °F (psi) | Status |
|---|---|---|---|
| Shell, UG-99 Note 35 | 23,210 | 32,400 (SA-516-70 N) | PASS |
| 2:1 SE heads | 26,000 | 32,400 | PASS |
| Component | Specification | S at 100 °F (psi) | UCS-66 Curve | Form |
|---|---|---|---|---|
| Shell | SA-516 Grade 70, normalized | 20,000 | D | 1.000 in plate, rolled and welded long seam |
| Heads (top and bottom, 2 ea) | SA-516 Grade 70, normalized | 20,000 | D | 2:1 ellipsoidal, one-piece formed, 0.875 in nominal |
| Nozzle necks | SA-106 Grade B, seamless | 17,100 | B | NPS 6 / 4 / 2 Schedule 80 pipe |
| Flanges | SA-105 | 20,000 | B | ASME B16.5 RFWN, Class 300, all four process nozzles |
| Bolting | SA-193 Gr B7 studs, SA-194 Gr 2H nuts | 25,000 | n/a | standard B16.5 stud-and-nut sets |
| Lifting lugs and skid attachment | SA-516 Gr 70 plate | n/a | n/a | Four lifting lugs on upper shell course, four skid clips on the lower head transition |
| Tag | Function | Size and Class | Location | Type | Weld |
|---|---|---|---|---|---|
| N1 | Process inlet | NPS 6 Cl 300 RFWN, Sch 80 neck | Top head | Set-in radial, no repad required (UG-37 PASS) | Full pen + fillet per UW-16(f) |
| N2 | Liquid outlet | NPS 4 Cl 300 RFWN, Sch 80 neck | Bottom head | Set-in radial, no repad required | Full pen + fillet per UW-16(f) |
| N3 | Pressure-relief (PSV) | NPS 2 Cl 300 RFWN, Sch 80 neck | Top head | Set-in radial, exempt under UG-36(c)(3)(a) | Full pen + fillet per UW-16(f) |
| N4 | Drain | NPS 2 Cl 300 RFWN, Sch 80 neck | Bottom head | Set-in radial, exempt under UG-36(c)(3)(a) | Full pen + fillet per UW-16(f) |
The NPS 6 inlet and NPS 4 outlet exceed the UG-36(c)(3)(a) 3.5 in finished-diameter exemption limit and require a UG-37 area-replacement calculation. Both pass without a repad on the 0.725 in corroded SE head wall.
The Category A long seam in the shell and both Category A head-to-shell circumferential welds are examined by full radiography per UW-11(a)(1). Nozzle attachment welds are examined by surface NDE per UW-50.
| Item | Value |
|---|---|
| Shell OD | 60.000 in |
| Shell wall, nominal | 1.000 in |
| Shell wall, mill-min (-12.5%) | 0.875 in |
| Shell wall, corroded (mill-min less CA) | 0.813 in |
| Shell tangent-to-tangent length | 96 in (8 ft) |
| Head nominal thickness (as-built, 2:1 SE) | 0.875 in |
| Head depth, D/4 (2:1 SE) | 14.5 in (inside crown) |
| Overall tangent-to-knuckle height (shell + 2 SE heads) | 96 + 2 × 16 = 128 in |
| Internal volume, new (shell + 2 SE heads) | 329,000 in³ (1,425 US gal) |
| Empty weight, new (shell + 2 SE heads + nozzles + lugs) | 6,250 lb |
| Empty weight, corroded | 5,900 lb |
| Test weight, water-filled | 18,130 lb |
Every clause applied in the analysis, grouped by topic. The substitutions and results for the most-asked clauses are written out in section 5. Section 5 also contains a four-way head-type comparison covering UG-32(c), UG-32(d), UG-32(f), and UG-34(c)(2) side by side.
| Clause | Component | Use |
|---|---|---|
| UG-16(b) | All | Minimum required thickness floor of 0.0625 in |
| UG-23 | All | Allowable stress tables, S-values at design temperature |
| UG-25 | All | Corrosion allowance, 0.0625 in on internal surfaces |
| UG-27(c)(1) | Cylindrical shell, nozzle necks | Required thickness for internal pressure, circumferential stress |
| UG-32(c) | Comparison only (F&D torispherical option) | Required thickness for F&D heads, M factor from crown / knuckle ratio |
| UG-32(d) | 2:1 SE heads (as-built) | Required thickness for 2:1 ellipsoidal heads, K = 1.00 |
| UG-32(f) | Comparison only (hemispherical option) | Required thickness for hemispherical heads, L = inside crown radius |
| UG-34(c)(2) | Comparison only (flat cover option) | Welded flat cover, Figure UG-34 Sketch (h), C = 0.33 |
| Clause | Use |
|---|---|
| UG-36(c)(3)(a) | Exempts NPS 2 PSV and drain; NPS 6 inlet and NPS 4 outlet require UG-37 (both PASS without repad) |
| UG-37 | Area replacement procedure on NPS 6 and NPS 4 |
| UG-41 | Strength of reinforcement, not invoked because no repad is required |
| UG-44 | Cl 300 RFWN flanges accepted at the standard P-T rating (720 psig at 100 °F) |
| 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-13.2 | Referenced in the head-comparison flat-cover option (Sketch (h)) |
| UW-15 / UW-16 / UW-50 | Nozzle welds and NDE |
| Clause | Use |
|---|---|
| UCS-66 / UCS-66.1 | MDMT qualification |
| UG-99(b) / Note 35 | Hydrotest at 645 psig |
| UG-116 / UG-118 / UG-120(c) | Nameplate, location, U-1A |
Five worked examples. The shell is example 1. The four head-type options are examples 2 through 5, each derived from first principles on the same 60 in OD shell at 400 psig and 100 °F so the resulting MAWPs, head depths, and weights are directly comparable.
Required thickness of the SA-516 Grade 70 Normalized cylindrical shell under 400 psig at 100 °F.
| Symbol | Value | Source |
|---|---|---|
| P | 400 psig | Design pressure |
| R | 29.188 in | Inside radius, corroded: ½ × (60 - 2 × 0.813) |
| S | 20,000 psi | SA-516 Gr 70 at 100 °F, ASME II-D Table 1A |
| E | 1.00 | Full RT long seam, Table UW-12 |
Required thickness is 0.591 in. Adding corrosion allowance gives t_total = 0.654 in. Mill-minimum supplied is 0.875 in, which leaves 0.813 in available after corrosion. PASS with 0.159 in margin between t_avail and t_total. Shell MAWP at the corroded condition is 548 psig.
Hemispherical option for the closure. The hemispherical head is the thinnest and lightest of the four options because it carries pure membrane stress with no bending; the trade-off is the deepest head (D/2 depth) which raises the overall vessel height.
| Symbol | Value | Source |
|---|---|---|
| P | 400 psig | Design pressure |
| L | 29.188 in | Inside crown radius, equal to shell R_corr for a hemi head |
| S | 20,000 psi | SA-516 Gr 70 at 100 °F |
| E | 1.00 | One-piece formed head |
Required thickness is 0.293 in. Adding corrosion allowance gives t_req = 0.355 in. Nominal head thickness ordered for the hemi option would be 0.500 in (1/2 in plate); after typical 10% forming thinning and the corrosion allowance, the in-service minimum is 0.388 in. PASS with 0.033 in margin.
The 2:1 SE head is the as-built closure for this vessel. It is the industry default because the head depth (D/4) is moderate and the required thickness is the same as a cylindrical shell of the same diameter.
| Symbol | Value | Source |
|---|---|---|
| P | 400 psig | Design pressure |
| D | 58.375 in | Inside diameter at the head skirt (shell ID, corroded) |
| S | 20,000 psi | SA-516 Gr 70 at 100 °F |
| E | 1.00 | One-piece formed head, Table UW-12 |
| K | 1.00 | 2:1 ellipsoidal aspect ratio, UG-32(d) |
Required thickness is 0.585 in. Adding corrosion allowance gives t_req = 0.648 in. Nominal head thickness ordered is 0.875 in (7/8 in plate); after typical 10% forming thinning and the corrosion allowance, the in-service minimum is 0.725 in. PASS with 0.077 in margin.
F&D (flanged and dished) torispherical option. Per ASME F&D conventions the crown radius L equals the head outside diameter and the knuckle radius r is typically 6% of the outside diameter (3.75 in for a 60 in OD head, slightly above the 6% rule, rounded for procurement). The M factor captures the elevated bending stress at the knuckle:
| Symbol | Value | Source |
|---|---|---|
| P | 400 psig | Design pressure |
| L | 60.000 in | Crown radius (F&D convention, L = OD) |
| r | 3.750 in | Knuckle radius (rounded from 6% of OD = 3.6 in) |
| L/r | 16.00 | Crown / knuckle ratio |
| M | 1.750 | (3 + √(L/r)) / 4 = (3 + 4) / 4 |
| S | 20,000 psi | SA-516 Gr 70 at 100 °F |
| E | 1.00 | One-piece formed head |
Required thickness is 1.052 in. Adding corrosion allowance gives t_req = 1.115 in. Nominal head thickness ordered for the F&D option would be 1.375 in (1-3/8 in plate); after typical 10% forming thinning and the corrosion allowance, the in-service minimum is 1.175 in. PASS with 0.060 in margin.
Flat-cover option. The welded flat cover is the simplest geometry but is the heaviest and most expensive at large diameters because the required thickness scales with diameter and the square root of pressure ratio rather than directly with pressure as a curved head does. The cover diameter `d` used in the UG-34 formula is the nominal shell inside diameter (corpus convention).
| Symbol | Value | Source |
|---|---|---|
| P | 400 psig | Design pressure |
| d | 58.000 in | Nominal shell ID (OD - 2 t_nom = 60 - 2 × 1.000) |
| S | 20,000 psi | SA-516 Gr 70 at 100 °F |
| E | 1.00 | Full RT cover weld |
| C | 0.33 | Figure UG-34 Sketch (h) |
Required thickness is 4.712 in. Adding corrosion allowance gives t_req = 4.775 in. Nominal flat-cover thickness ordered for this option would be 5.000 in plate (cut from heavy SA-516-70 N plate). PASS with 0.225 in margin.
All four head options PASS the 400 psig design pressure on the same 60 in OD shell. The trade-offs are visible in the summary table below.
| Head type | Clause | t_nom (in) | MAWP (psig) | Inside head depth (in) | Single-head weight (lb) |
|---|---|---|---|---|---|
| Hemispherical | UG-32(f) | 0.500 | 530 | 29.2 | 757 |
| 2:1 SE (as-built) | UG-32(d) | 0.875 | 496 | 14.6 | 1,019 |
| F&D torispherical | UG-32(c) | 1.375 | 447 | 10.5 | 1,450 |
| Welded flat cover | UG-34(c)(2) | 5.000 | 439 | 0.0 | 4,000 |
Reading the table: the hemispherical head is the thinnest and lightest by a wide margin (about 25% of the flat-cover weight and 75% of the SE weight) and carries the highest MAWP, but the head depth is the full inside radius, which adds 29 in of overall vessel height per end and complicates fabrication of the deep crown. The 2:1 SE is the standard industry pick because the moderate head depth and the standard pipe-and-plate fab procedure outweigh the thickness penalty over a hemi. The F&D is shallowest of the curved options but is heavier because of the M factor on the knuckle bending. The welded flat cover is rarely used at this diameter because the thickness scales poorly; on small vessels (NPS 12 and below, see the 8 in NPS page in the related links) the flat cover is the practical choice.
60 in OD vertical pressure vessels at 400 psig design pressure are common in mid-stream gas processing as scrubbers, knockout drums, filter housings, and amine flash drums. The teaching value of the example is the head-type comparison: a hemispherical head is more than three-quarters lighter than a welded flat cover on the same shell at the same pressure but adds 29 in of overall height per end, while a welded flat cover is more than five times heavier than the SE and is rarely used above NPS 12. The 2:1 SE is the industry default for vessels in this size range because the depth and weight are both moderate and the pipe-and-plate fabrication procedure is standard.