Vessel Wall Thickness — ASME VIII Div 1 (Approximate)

First-pass wall thickness for a cylindrical pressure vessel on internal pressure — the UG-27 shell equation and the UG-32 head equation, worked in the corroded condition, rounded up to a plate you can actually buy, and turned back around into the MAWP that plate will hold. Pick a material and a design temperature and the allowable stress follows.

Preliminary sizing only — this is not a design calculation

Preliminary sizing only. Excludes nozzle reinforcement (UG-37), external pressure (UG-28), liquid static head, wind/seismic and attachment loads, and plate under-tolerance. Final design must be performed to the current ASME code edition by a qualified vessel designer.

Design conditions

Design pressure (internal, gauge) (psig)Inside diameter (new, uncorroded) (in)Corrosion allowance (in)

Sacrificial metal. The wall is sized for the bore after it corrodes away (48.25 in inside), then the allowance is added back on.

Design temperature (°F)

Material

Carbon steel plate, 70 ksi UTS — the default vessel plate

S at 200 °F = 20,000 psi (table covers -20–650 °F). Approximate Section II-D Table 1A values, post-1999 3.5:1 margin.

Construction

Joint efficiency E

How much the weld seam is trusted (Table UW-12). More radiography means a thinner, cheaper wall — the trade is inspection cost against plate cost.

Head type

The workhorse head: depth = 1/4 of the diameter. Costs a little more than F&D but is thinner and shorter than a hemi.

What to buy

Recommended plate

0.375in

Smallest stock plate covering 0.339 in

Governing MAWP at that plate

175.1psig

Shell governs · corroded, 0.250 in of metal left

Allowable stress used

20,000psi

SA-516-70 at 200 °F · E = 0.85

Nominal shell thickness

0.339in

0.214 in required + 0.125 in corrosion

Nominal head thickness

0.338in

2:1 Ellipsoidal · 0.213 in required + corrosion

Longitudinal seam (info)

0.106in

About half the hoop requirement — never governs a plain cylinder

How thickness grows with pressure

Shell (UG-27)2:1 Ellipsoidal head (UG-32)Nominal (corrosion included)

Show the full calculation & assumptions

1 · Corroded geometry

Inside radius R = 24.00 in + 0.13 in = 24.13 in
Inside diameter D = 48.25 in
S = 20,000 psi, E = 0.85 → S·E = 17,000 psi

2 · Shell — UG-27(c)

t = P·R / (S·E − 0.6·P) (circumferential stress — governs)

t = 0.214 in
longitudinal seam t = P·R / (2·S·E + 0.4·P) = 0.106 in (information only)
nominal = 0.214 in + 0.125 in = 0.339 in

3 · Head — UG-32(d), 2:1 Ellipsoidal

t = P·D / (2·S·E − 0.2·P)

t = 0.213 in
nominal = 0.338 in

4 · Thin-wall validity (UG-27)

P = 150.0 psig vs 0.385·S·E = 6,545.0 psig
t = 0.214 in vs 0.5·R = 12.063 in
Both satisfied — UG-27 applies.

5 · Plate selection and MAWP

governing nominal = max(shell, head) = 0.339 in → plate 0.375 in
corroded metal available = plate − corrosion = 0.250 in
shell MAWP = S·E·t / (R + 0.6·t) = 175.1 psig
head MAWP = 176.0 psig
governing MAWP = 175.1 psig — the shell sets it

Allowable stresses are approximations of Section II-D Table 1A on the post-1999 3.5:1 design margin, interpolated linearly between table points. Joint efficiencies are Table UW-12 values for Type 1 double-welded butt joints. Use the current code edition for anything that gets built.

Read before you rely on these numbers

Internal pressure only. A vessel under vacuum or external jacket pressure is a buckling problem (UG-28) and usually needs a thicker wall or stiffening rings.
Nozzles are not here. Every opening removes pressure-carrying metal and has to be replaced under UG-37 — that often drives the shell thicker than this number, or adds a reinforcing pad.
No liquid static head, no wind or seismic, no saddle, lug or nozzle loads, no plate under-tolerance or forming thinout on the head.
Material allowable stresses here are approximate. Low-temperature service also needs an impact-test (UCS-66) review that this tool does not perform.
Preliminary sizing only. Excludes nozzle reinforcement (UG-37), external pressure (UG-28), liquid static head, wind/seismic and attachment loads, and plate under-tolerance. Final design must be performed to the current ASME code edition by a qualified vessel designer.