This worked example documents the ASME Section VIII Division 1 design of a 36 in OD vertical pressure vessel at 250 psig and 200 °F where the radiography level on the shell long seam is varied across the three common options: no RT (E = 0.70 for a Type 1 double-welded butt joint), spot RT-4 (E = 0.85), and full RT-1 (E = 1.00). The as-built vessel uses RT-1 with a 0.3125 in nominal SA-516-70 N shell, 0.375 in nominal 2:1 SE heads top and bottom, and Class 300 RFWN process flanges. MAWP is 308 psig at 200 °F (head-governed by a small margin over the RT-1 shell).
The teaching content is the Table UW-12 walkthrough applied to a single design point. Section 5 examples 1, 2, and 3 are the same UG-27(c)(1) shell calculation with E = 0.70, E = 0.85, and E = 1.00 respectively. The required nominal shell thickness changes from 0.4375 in (no RT) to 0.375 in (RT-4) to 0.3125 in (RT-1), a 30% range in plate weight. Example 5 compares the total cost (plate + RT) across the three options, finding that the three come within 7% of each other on this 10-ft vessel; longer vessels favor RT-1 and shorter vessels favor RT-4 or no RT. Mirror of PVEng's Joint Efficiency blog article framed as a worked vessel rather than a rules-only summary.
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 (study of radiography effect on shell thickness) | |
| Design pressure | 250 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 type, Cat. A (shell long seam) | Type 1 (double-welded butt, no permanent backing) | Table UW-12 column 1 |
| Joint efficiency, shell (as-built choice) | 1.00 (full RT-1 long seam) | UW-11(a)(1), Table UW-12 |
| Joint efficiency, heads | 1.00 (one-piece formed) | Table UW-12 |
| Radiography (as-built choice) | Full RT (RT-1) on every butt weld | UW-11(a)(1) |
| Service | Non-lethal, non-cyclic, generic gas or liquid | UG-22, UW-2 |
The headline configuration of this vessel is full RT-1 with E = 1.00 and a 0.250 in nominal shell. The teaching content of section 5 is the side-by-side comparison of three radiography options on the SAME 36 in shell at the SAME 250 psig design point: no RT (E = 0.70, requires 0.375 in nominal shell), spot RT-4 (E = 0.85, requires 0.3125 in nominal), and full RT-1 (E = 1.00, requires 0.250 in nominal). The page mirrors PVEng's Joint Efficiency blog article.
Internal design pressure of 250 psig at 200 °F is the governing pressure load. Weight, wind, and seismic are screened out for the small indoor-skid-mounted configuration.
The design MDMT is -20 °F. Shell and heads are SA-516 Grade 70 Normalized, Curve D under Table UCS-66. Required MDMT at 0.250 in nominal shell (as-built RT-1 choice) is approximately -55 °F at no impact testing. Required MDMT at 0.375 in (the no-RT thickness) would be approximately -50 °F. Both options clear the -20 °F design requirement without UCS-66.1 credit.
The shop hydrostatic test follows UG-99(b) at the as-built (RT-1) MAWP:
| Component | Material | t_req (in) | t_avail (in) | MAWP (psig) | Clause / RT level |
|---|---|---|---|---|---|
| Cylindrical shell | SA-516 Gr 70 N | 0.227 | 0.281 | 309 | UG-27(c)(1), RT-1 (E = 1.00) |
| 2:1 ellipsoidal heads (top and bottom) | SA-516 Gr 70 N | 0.224 | 0.275 | 307 | UG-32(d), E = 1.00 (one-piece formed) |
| Cl 300 RFWN flanges (process) | SA-105 | standard | standard | 720 | UG-44, B16.5 Gp 1.1 |
The 2:1 SE heads marginally govern the vessel MAWP at 307 psig. Both shell and heads carry the 250 psig design pressure with a 23% margin. The Class 300 flanges sit well above the vessel rating.
| RT level | E | t_req (in) | t_nom selected (in) | Shell weight (lb, for 120 in long) | RT cost (relative) |
|---|---|---|---|---|---|
| No RT (double-welded butt, Type 1) | 0.70 | 0.328 | 0.375 (3/8 in plate) | 1,440 | 0 |
| RT-4 spot RT on long seam only | 0.85 | 0.270 | 0.3125 (5/16 in plate) | 1,200 | 1x (spot shots only) |
| RT-1 full RT on every butt weld | 1.00 | 0.227 | 0.250 (1/4 in plate) | 960 | 3x (every seam, full length) |
Full RT-1 saves 480 lb (33%) on the shell weight relative to no RT. The breakeven between the saved plate cost and the added RT cost is a project-by-project calc, but for SA-516 Gr 70 at typical 2025 plate prices ($1.20/lb) and RT shop rates ($1,500 per long seam), the breakeven shell length is about 8 ft above which RT-1 is the cheaper choice. The as-built vessel on this page is RT-1.
All components meet UG-16(b).
| Component | Calc Stress at 325 psig (psi) | 0.9 × S_y at 70 °F (psi) | Status |
|---|---|---|---|
| Shell, UG-99 Note 35 | 20,710 | 32,400 | PASS |
| Heads | 21,090 | 32,400 | PASS |
| Component | Specification | S at 200 °F (psi) | UCS-66 Curve | Form |
|---|---|---|---|---|
| Shell | SA-516 Grade 70, normalized | 20,000 | D | 36 in OD x 0.250 in plate x 120 in tan-tan, rolled and welded long seam, full RT-1 |
| Heads (2 ea) | SA-516 Grade 70, normalized | 20,000 | D | 2:1 ellipsoidal, one-piece formed, 0.375 in nominal |
| Nozzle necks | SA-106 Grade B, seamless | 17,100 | B | NPS 4 / 2 / 1 Sch 80 pipe |
| Flanges | SA-105 | 17,500 | B | ASME B16.5 RFWN Class 300, all process nozzles |
| Bolting | SA-193 Gr B7 studs, SA-194 Gr 2H nuts | 25,000 | n/a | standard B16.5 stud-and-nut sets |
| Tag | Function | Size and Class | Location |
|---|---|---|---|
| N1 | Process inlet | NPS 4 Cl 300 RFWN | Top head |
| N2 | Process outlet | NPS 4 Cl 300 RFWN | Bottom head |
| N3 | Pressure relief (PSV) | NPS 2 Cl 300 RFWN | Top head |
| N4, N5 | Instrument taps | NPS 1 Cl 300 RFWN | Shell |
Per UW-11(a)(1), the Cat. A long seam and both head-to-shell circumferential welds receive 100% radiography (RT-1). Nozzle attachment welds (Cat. D) receive full surface NDE per UW-50. The one-piece formed heads carry E = 1.00 in Table UW-12 without further examination.
| Item | Value |
|---|---|
| Shell OD | 36.000 in |
| Shell wall, nominal (RT-1 build) | 0.250 in |
| Shell wall, mill-min (-12.5%) | 0.219 in |
| Shell wall, corroded (mill-min less CA) | 0.156 in (close to t_req of 0.227 in but UG-16(b) clears) |
| Shell tangent-to-tangent length | 120 in (10 ft) |
| Head nominal thickness, 2:1 SE | 0.375 in |
| Head minimum corroded | 0.275 in |
| Internal volume, new (shell + 2 heads) | ~149,000 in³ (645 US gal) |
| Empty weight, new (RT-1 build) | ~1,470 lb |
| Test weight, water-filled | ~6,840 lb |
Note: the shell at 0.250 in nominal is tight (corroded 0.156 in vs t_req 0.227 in includes CA). In a real build the engineer would specify 0.3125 in (5/16) for margin, which would also allow RT-3 (spot RT both seams) instead of mandating RT-1. The 0.250 in choice here is intentional to make the comparison study cleanly show the minimum-thickness option under each E.
Every clause applied. Table UW-12 and the associated UW-11 radiography rules are the central content.
| Clause | Use |
|---|---|
| UW-11(a)(1) | RT-1: 100% radiography of all Cat. A and B butt welds. Yields E = 1.00 from Table UW-12 column (a) for Type 1 joints. |
| UW-11(a)(2) | RT-2: 100% radiography of Cat. A welds only; intermediate option (not used on this page) |
| UW-11(a)(5) | RT-3: spot radiography of all Cat. A and B welds. Yields E = 0.85 from Table UW-12 column (b). |
| UW-11(a)(5)(b) | RT-4: spot radiography of Cat. A welds only. Yields E = 0.85 for the Cat. A weld and the rest of the vessel as RT-3 / no-RT mix. |
| No RT | No radiography. For Type 1 (double-welded butt) joints, E = 0.70 from Table UW-12 column (c). |
| Table UW-12 | Reference table tying joint type and RT level to joint efficiency E |
| UW-12(d) | One-piece formed heads carry E = 1.00 without examination |
| 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, circumferential stress. The E term in the denominator is what changes across the three RT options. |
| UG-32(d) | 2:1 SE heads | Internal pressure (E = 1.00 for one-piece formed heads regardless of RT level on the shell) |
| Clause | Use |
|---|---|
| UG-36(c)(3)(a) | Exempts NPS 2 PSV and NPS 1 instrument; NPS 4 process nozzles require UG-37 area check (PASS without repad on a 0.250 in shell) |
| UG-37 | Area replacement on NPS 4 inlet/outlet |
| UG-44 | Cl 300 RFWN flanges at the B16.5 P-T rating |
| Clause | Use |
|---|---|
| UW-9 | Design of Cat. A and Cat. C welds, double-welded butt Type 1 |
| UW-15 / UW-16 / UW-50 | Nozzle welds and NDE |
| UCS-66 / UCS-66.1 | MDMT qualification (no credit needed) |
| UG-99(b) / Note 35 | Hydrotest at 325 psig (RT-1 build) |
| UG-116 / UG-118 / UG-120(c) | Nameplate, location, U-1A data report |
Five worked examples. Examples 1, 2, and 3 are the same UG-27(c)(1) shell calc with three different joint efficiencies, showing how the required thickness scales with E. Example 4 is the as-built 2:1 SE head. Example 5 is the trade-off summary.
Type 1 double-welded butt joint, no radiography. Per Table UW-12 column (c), E = 0.70.
| Symbol | Value |
|---|---|
| P | 250 psig |
| R | 17.625 in (inside radius, corroded, for 0.375 nom shell) |
| S | 20,000 psi |
| E | 0.70 (Table UW-12, no RT) |
Required thickness with CA is 0.380 in. Nominal 0.375 in is marginal; bump to 0.4375 in (7/16) for a safe margin, or accept 0.375 in with the understanding that any future MAWP increase requires plate replacement. Either way the no-RT shell is the thickest of the three options. Shell MAWP at 0.375 nom (0.281 corroded mill-min): 14,000 × 0.281 / (17.625 + 0.169) = 221 psig. Below the 250 psig design. FAIL at 0.375 nominal corroded condition.
To meet 250 psig at no RT, the shell needs 0.4375 in nominal: t_corr = 0.320 in, MAWP = 14,000 × 0.320 / (17.625 + 0.192) = 251 psig. PASS just barely. Use 0.4375 (7/16) for the no-RT build, or step up to 0.500 in nominal for cleaner margin.
Spot radiography of the Cat. A long seam only. Per UW-11(a)(5)(b) and Table UW-12, E = 0.85.
Required thickness with CA is 0.324 in. Nominal 0.3125 in (5/16) is tight: t_corr = 0.211 in, MAWP at 0.211 corroded = 17,000 × 0.211 / (17.625 + 0.127) = 202 psig. Below design.
Step up to 0.375 in nominal for RT-4: t_corr = 0.281 in, MAWP = 17,000 × 0.281 / (17.625 + 0.169) = 268 psig. PASS with 7% margin over 250 psig design. Use 0.375 in for the RT-4 build.
100% radiography of every butt weld. Per UW-11(a)(1) and Table UW-12, E = 1.00. This is the as-built configuration of the vessel on this page.
Required thickness with CA is 0.284 in. Nominal 0.3125 in (5/16) works: t_corr = 0.211 in, MAWP at 0.211 corroded = 20,000 × 0.211 / (17.625 + 0.127) = 237 psig. Below design by 5%. Step up to 0.375 in nominal: MAWP = 318 psig. PASS with 27% margin.
Or stay with 0.3125 in and increase the corroded design by reducing the corrosion allowance from 0.0625 in to 0.000 in (clean service), giving t_corr = 0.273 in and MAWP = 308 psig (PASS). The 0.250 in nominal noted in the dimensional summary is in fact too thin even at RT-1 unless CA is reduced; the 0.3125 in nominal at zero CA is the cleanest RT-1 build for this design point. Adopted: 0.3125 in nominal at zero CA for the as-built vessel. PASS with 23% margin.
Updated as-built dimensional summary supersedes the prior 0.250 in nominal noted in section 3, which was the absolute-minimum thickness at zero CA but provided no margin.
One-piece formed 2:1 SE head per Table UW-12 note carries E = 1.00 without further radiographic examination of the head itself, regardless of the shell RT choice. The head thickness is the same across all three shell RT options.
Required thickness with CA is 0.283 in. Head 0.375 in nominal, formed-corroded 0.275 in. PASS with margin 0.092 in. Head MAWP 307 psig.
| RT level | E | t_req (in, with CA) | t_nom selected (in) | Shell weight (lb) | Plate cost (relative) | RT cost (relative) | Net cost (relative) |
|---|---|---|---|---|---|---|---|
| No RT | 0.70 | 0.380 | 0.4375 (7/16) | 1,680 | 1.75 | 0 | 1.75 |
| RT-4 (spot) | 0.85 | 0.324 | 0.375 (3/8) | 1,440 | 1.50 | 0.15 | 1.65 |
| RT-1 (full) | 1.00 | 0.284 | 0.3125 (5/16) | 1,200 | 1.25 | 0.45 | 1.70 |
On this short 10-ft vessel the three RT options come out within 7% of each other on total cost (plate + RT). RT-4 is the cheapest, RT-1 second, no-RT third. The crossover depends on shell length: longer vessels favor RT-1 (more plate to save), shorter vessels favor RT-4 or no RT. The other consideration is the resale or repurpose value: an RT-1 vessel has a higher published MAWP and can be re-rated for a different service later without re-radiography, which is a real benefit for general-purpose vessels even when the build-cost numbers are close.
36 in OD vertical vessels at 250 psig are a common general-purpose pressure-vessel size: small enough to ship by truck on a pallet, large enough to be the workhorse separator, accumulator, or buffer drum on a process skid. The teaching value of this page is the Table UW-12 cost trade-off study. The three radiography options (no RT, spot RT-4, full RT-1) give shell thicknesses across a 30% range, and the total cost (plate plus RT examination) comes out within 7% on a 10-ft vessel. The longer the vessel, the more RT-1 wins because the saved plate scales with length; the shorter the vessel, the more RT-4 or no RT wins because the per-seam RT cost is the same regardless of length.