This worked example documents the ASME Section VIII Division 1 design of an 8 in NPS vertical pressure vessel built from Schedule 40 pipe, at a design pressure of 285 psig and 200 °F. The vessel uses a B16.9 cap on top, a welded flat cover on the bottom, and three threaded couplings for process inlet, drain, and vent. MAWP is 450 psig at the bottom cover, and the shop hydrostatic test pressure is 585 psig.
The analysis follows the 2023 Edition of ASME Section VIII Division 1. Every code clause used in the rating is listed in section 4, and the four governing calculations (shell wall, B16.9 cap, flat cover, nozzle reinforcement) are written out with full substitutions in section 5. The vessel is rated to -55 °F MDMT at full MAWP, with the bottom cover plate as the governing component. This page is a generic worked example, not a project record, and should not be used as the basis for a built unit.
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 | 285 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 (seamless pipe per Table UW-12) | UW-12 |
| Joint efficiency, cover weld | 1.00 (full RT, Cat. A circumferential) | UW-11, UW-12 |
| Radiography | Full RT on Cat. A welds, surface NDE on nozzle welds | UW-11, UW-51, UW-50 |
| Service | Non-lethal, non-cyclic | UG-22, UW-2 |
The vessel is analyzed for the loadings listed in UG-22. Governing loads for this configuration are:
External pressure, wind, seismic, and cyclic service are not credible for this configuration. The vessel is non-cyclic per UG-22(e) screening, so an explicit fatigue check is not required.
The Minimum Design Metal Temperature is -20 °F at the full design pressure of 285 psig. Each pressure-boundary component is qualified to the design MDMT by the methods of UCS-66 and UCS-66.1:
The bottom cover governs the published rated MDMT. The vessel is rated to -55 °F at full MAWP, which is 35 °F colder than the -20 °F design MDMT requirement.
The shop hydrostatic test follows UG-99(b). Test pressure is 1.3 times MAWP at design temperature multiplied by the lowest stress ratio across pressure-boundary components, with water at 70 °F in the vertical orientation:
The lowest stress ratio is 1.00 because both SA-53 Grade B and SA-516 Grade 70 carry their full allowable stress at 70 °F relative to 200 °F (the design temperature is well below the temperature where these materials begin to derate).
| Component | Material | t_req (in) | t_avail (in) | MAWP (psig) | Clause |
|---|---|---|---|---|---|
| Cylindrical shell | SA-53 Gr B | 0.069 | 0.220 | 890 | UG-27(c)(1) |
| Top cap, ASME B16.9 | SA-234 WPB | 0.058 | 0.282 min | matches pipe (890) | UG-44, B16.9 Table 4 |
| Bottom flat cover | SA-516 Gr 70 N | 0.547 | 0.688 | 450 | UG-34(c)(2) |
| Inlet nozzle, NPS 2 Cl. 6000 | SA-105 | exempt | 0.40 body | matches shell | UG-36(c)(3), UG-43 |
The bottom flat cover governs the vessel MAWP at 450 psig. The shell carries the design pressure with a margin of three to one between t_avail and t_req. The B16.9 top cap inherits the pipe rating per B16.9 Table 4 and is not the governing closure.
Per UG-16(b), the minimum required thickness of any pressure-retaining wall is the larger of the calculated required thickness and 0.0625 in (1/16 in). All components meet UG-16(b). The shell at 0.220 in (corroded, mill-min) is 0.158 in above the UG-16(b) floor. The cover at 0.688 in (corroded) is 0.625 in above.
| Component | Calc Stress at 585 psig (psi) | 0.9 × S_y at 70 °F (psi) | Status |
|---|---|---|---|
| Shell, UG-99 Note 35 | 5,455 | 31,500 | PASS |
| Bottom cover | 26,030 | 34,200 | PASS |
Calculated test stresses are well below the 0.9 × S_y limit of UG-99(b) Note 35 for both controlling components. No bolt or gasket check is required (no bolted joints in this configuration).
| Component | Specification | S at 200 °F (psi) | UCS-66 Curve | Form |
|---|---|---|---|---|
| Shell | SA-53 Grade B, seamless | 17,100 | B | NPS 8 Sch 40 pipe |
| Top cap | SA-234 Grade WPB | 20,000 | B | NPS 8 ASME B16.9 cap, wall ≥ pipe nom |
| Bottom cover | SA-516 Grade 70, normalized | 20,000 | D | 0.75 in plate, OD 8.625 in disc |
| Process inlet half-coupling | SA-105 | 20,000 | B | NPS 2 Cl. 6000 per ASME B16.11 |
| Drain half-coupling | SA-105 | 20,000 | B | NPS 0.5 Cl. 6000 per ASME B16.11 |
| Vent half-coupling | SA-105 | 20,000 | B | NPS 0.5 Cl. 6000 per ASME B16.11 |
| Tag | Function | Size and Class | Location | Type | Weld |
|---|---|---|---|---|---|
| N1 | Process inlet | NPS 2 Cl. 6000 threaded half-coupling | Shell | Set-on, radial | Full pen + fillet per UW-16(f) |
| N2 | Drain | NPS 0.5 Cl. 6000 threaded half-coupling | Bottom cover | Set-on | Full pen + fillet per UW-16(f) |
| N3 | Vent / instrument | NPS 0.5 Cl. 6000 threaded half-coupling | Top cap | Set-on | Full pen + fillet per UW-16(f) |
All three openings are below the size limit of UG-36(c)(3)(a) (3.5 in finished diameter) for a shell of 0.282 in thickness. Detailed reinforcement calculations under UG-37 are not required for any opening on this vessel. The verification calculation in section 5 confirms the area exemption.
The Category A weld between the bottom cover and the shell is examined by full radiography per UW-11(a)(1), giving E = 1.00. The seamless shell pipe carries E = 1.00 in Table UW-12 without further examination. The Category C weld between the top cap and the shell is examined by full radiography (or 100% UT per UW-11(a)(7) at the manufacturer's option). Nozzle attachment welds are examined by surface NDE (MT or PT) per UW-50.
| Item | Value |
|---|---|
| Shell OD | 8.625 in |
| Shell wall, nominal (Sch 40) | 0.322 in |
| Shell wall, mill-min (-12.5%) | 0.282 in |
| Shell wall, corroded (mill-min less CA) | 0.220 in |
| Shell tangent-to-tangent length | 52 in |
| Bottom cover thickness | 0.75 in |
| Bottom cover OD | 8.625 in (matches shell OD) |
| Top cap (ASME B16.9 NPS 8 Sch 40) | per B16.9 dimensional table |
| Internal volume, new | 410 in³ (1.78 US gal) |
| Empty weight, new | 150 lb |
| Empty weight, corroded | 140 lb |
| Test weight, water-filled | 245 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.
| 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 | Required thickness for internal pressure, circumferential stress |
| UG-32(d) | Top cap | 2:1 ellipsoidal-head check on the B16.9 cap, used as verification against B16.9 Table 4 rating |
| UG-34(c)(2) | Bottom cover | Welded flat cover, Figure UG-34 Sketch (h), C = 0.33 |
| Clause | Use |
|---|---|
| UG-36(c)(3)(a) | Exempts the NPS 2, NPS 0.5, NPS 0.5 openings on a 0.282 in shell from detailed UG-37 reinforcement calculation |
| UG-37 | Area replacement procedure, run as a verification (section 5) |
| UG-41 | Strength of reinforcement, not invoked because the area exemption applies |
| UG-43(d) | Threaded openings, half-couplings permitted |
| UG-44 | Flanges and pipe fittings, B16 standards accepted |
| UG-45 | Nozzle minimum-thickness check on each coupling neck |
| Clause | Use |
|---|---|
| UW-9 | Design of welded joints, Category A and Category C |
| UW-11(a)(1) | Full radiography on the Category A cover weld |
| Table UW-12 | Joint efficiency E = 1.00 for fully radiographed butt welds and seamless shell |
| UW-13.2 | Welded flat-head attachment, weld sizing for Sketch (h) |
| UW-15 | Strength of attachment welds, nozzle to shell |
| UW-16 | Minimum requirements for nozzle attachment welds |
| UW-50 | Final NDE on nozzle attachment welds (MT or PT, full surface) |
| Clause | Use |
|---|---|
| UCS-66 | Required MDMT at the actual component thickness, Fig UCS-66 curves |
| UCS-66.1 | Stress-ratio MDMT reduction, Fig UCS-66.1 |
| UCS-66(b) | Exemption rules for fittings and standard products |
| Clause | Use |
|---|---|
| UG-99(b) | Standard hydrostatic test, 1.3 × MAWP × LSR |
| UG-99(b) Note 35 | Stress at test pressure check against 0.9 × S_y |
| Clause | Use |
|---|---|
| UG-116 | Nameplate marking, U stamp |
| UG-118 | Nameplate location and attachment |
| UG-120(c) | Manufacturer's Data Report, Form U-1A |
Four worked examples. Each shows the inputs, the equation, the substitution with units, and the result. Example numbering is independent of the clause numbers used elsewhere on the page.
Required thickness of the SA-53 Grade B cylindrical shell under 285 psig at 200 °F.
| Symbol | Value | Source |
|---|---|---|
| P | 285 psig | Design pressure |
| R | 4.093 in | Inside radius, corroded: ½ × (8.625 - 2 × (0.282 - 0.0625)) |
| S | 17,100 psi | SA-53 Gr B at 200 °F, ASME II-D Table 1A |
| E | 1.00 | Seamless pipe, Table UW-12 |
Adding corrosion allowance gives t_total = 0.0689 + 0.0625 = 0.131 in required. Mill-minimum supplied is 0.282 in, which leaves 0.220 in available after corrosion. PASS, with 0.151 in margin between t_avail and t_total.
Shell MAWP is 890 psig at the mill-minimum corroded condition. The shell is not the governing component for this vessel.
The top closure is an ASME B16.9 NPS 8 Schedule 40 cap, SA-234 Grade WPB. Per UG-44, ASME B16.9 fittings are accepted at the pressure rating of the matching pipe, which is 890 psig at this configuration.
As an independent check, the cap is verified using the UG-32(d) 2:1 ellipsoidal-head formula. The B16.9 cap geometry is closer to a 2:1 ellipsoid than a torispherical, so K = 1.00:
| Symbol | Value | Source |
|---|---|---|
| P | 285 psig | Design pressure |
| D | 8.061 in | Inside diameter at the matching pipe (ID of NPS 8 Sch 40 pipe) |
| S | 20,000 psi | SA-234 WPB at 200 °F |
| E | 1.00 | Seamless forging |
| K | 1.00 | 2:1 aspect ratio, UG-32(d) |
Adding corrosion allowance gives t_req = 0.0575 + 0.0625 = 0.120 in. The B16.9 cap minimum wall is 0.282 in (mill-min Sch 40). PASS with 0.162 in margin. The cap is non-governing.
The bottom closure is a welded flat cover from 0.75 in SA-516 Grade 70 Normalized plate. Attachment is a full-penetration weld with a retainer fillet per UW-13.2, matching Figure UG-34 Sketch (h). The attachment factor C = 0.33 from Table UG-34 applies, with no credit taken for shell stiffness:
| Symbol | Value | Source |
|---|---|---|
| P | 285 psig | Design pressure |
| d | 7.981 in | Diameter at the weld (shell ID, mill-min) |
| S | 20,000 psi | SA-516 Gr 70 at 200 °F |
| E | 1.00 | Full RT cover weld |
| C | 0.33 | Figure UG-34 Sketch (h) |
Adding corrosion allowance gives t_req = 0.547 + 0.0625 = 0.610 in. Actual thickness is 0.75 in. PASS with 0.140 in margin.
The bottom flat cover sets the vessel MAWP at 450 psig. A thicker plate or a Sketch (j) retainer-ring detail would raise this number; for this example the 0.75 in plate is the chosen build.
The process inlet is a NPS 2 Class 6000 threaded half-coupling, SA-105 forging, welded radial into the shell. Per UG-36(c)(3)(a), openings with finished diameter not exceeding 3.5 in in a shell of 0.282 in thickness do not require reinforcement calculation under UG-37. The 2.067 in coupling bore is well below the 3.5 in limit, so UG-37 is not invoked by code.
The UG-37 area calculation is shown below as a verification, not as a code requirement.
| Symbol | Value | Source |
|---|---|---|
| d | 2.067 in | Finished opening, NPS 2 ID |
| t_r | 0.0689 in | Shell required thickness from Example 1, F = 1.0 |
| t | 0.220 in | Shell wall, corroded mill-min |
| t_n | 0.400 in | Coupling body wall, ASME B16.11 Cl. 6000 NPS 2 |
| F | 1.00 | Radial opening in cylindrical shell, Fig UG-37 |
| f_r1 | 1.00 | S_n / S_v capped at 1.0 (S_n = 20,000, S_v = 17,100) |
A1 alone (0.312 in²) exceeds A_required (0.142 in²) by 120%. PASS. Nozzle wall excess area (A2) and weld leg area (A3) are not needed and are not computed.
The same check applied to N2 (NPS 0.5 drain) and N3 (NPS 0.5 vent / instrument) gives larger margins because both openings are smaller. Both qualify under UG-36(c)(3)(a) by inspection.
8 in NPS vertical vessels at 285 psig design pressure are common in upstream and midstream gas processing as small knock-out pots, sample vessels, and skid-mounted drum closures. The configuration uses standard pipe and standard B16.9 and B16.11 fittings, which keeps fabrication cost low and lets the vessel be built without rolling plate. The teaching value of the example is the contrast between the shell (rated at 890 psig with margin to spare) and the bottom flat cover (rated at 450 psig, the governing component): a small change in cover thickness or in the UG-34 attachment sketch moves the vessel MAWP up or down by a large amount.