Pressure Vessel Design (ASME VIII)

Quick pick (TL;DR)

Shell thickness (ASME VIII Div 1, internal pressure): t = P·R / (S·E − 0.6·P), then add the corrosion allowance.
S is the material allowable at the design temperature, E the weld joint efficiency (1.0 full RT, 0.85 spot, 0.7 none).
Use 2:1 ellipsoidal heads as the default.
Check nozzle reinforcement, decide PWHT & radiography by thickness/service, and protect with a relief valve.

Step 1 — Inputs

Input	Source	Note
Design P & T	Process	MAWP
S (allowable)	ASME II-D	Temp-dependent
E (joint eff.)	RT level	1.0 / 0.85 / 0.7
CA	Service	Add on

Step 2 — Worked shell thickness

ID 2000, 15 barg, SA-516-70

ASME VIII Div 1 t = P·R / (S·E − 0.6·P) Given P = 15 barg = 1.5 MPa R = ID/2 = 1000 mm S = 138 MPa , E = 0.85 Step 1 — Compute t = 1.5 × 1000 / (138×0.85 − 0.6×1.5) t = 1500 / (117.3 − 0.9) = 1500/116.4 t = 12.9 mm Step 2 — Add CA t + CA = 12.9 + 3 = 15.9 mm → select 16 mm plate

Membrane formula for hoop stress; E penalises un-radiographed welds; use S at design temperature.

Step 3 — Heads & fabrication

2:1 ellipsoidal default; hemi for high P.
Reinforce nozzles (UG-37).
PWHT/RT by service; always relief.

Shell thickness calculator (ASME VIII)

Internal-pressure shell thickness

t = P·R / (S·E − 0.6·P) + corrosion allowance.

Design pressure (barg)

ID (mm)

Allowable S (MPa)

Joint efficiency E

Corrosion allow. (mm)

Hoop stress, internal pressure. Use S at design temp; add nozzles & heads.

Common mistakes

Ambient S for a hot vessel.
Forgetting CA / nozzle reinforcement.
No overpressure relief.

Requisition & datasheet

Type, ID, P/T, CA, material.
S, E, thickness, heads, PWHT/RT.

Frequently asked questions

What should I know about Pressure Vessel Design (ASME VIII)?

Shell thickness (ASME VIII Div 1, internal pressure): t = P·R / (S·E − 0.6·P), then add the corrosion allowance. S is the material allowable at the design temperature, E the weld joint efficiency (1.0 full RT, 0.85 spot, 0.7 none). Use 2:1 ellipsoidal heads as the default. Check nozzle reinforcement, decide PWHT & radiography by thickness/service, and protect with a relief valve.

Which standards or codes apply?

ASME VIII Div 1 & 2 (pressure vessels), ASME II-D (allowable stress), PD 5500, EN 13445, NACE MR0175 (sour), API 510 (inspection).

Standards — ASME VIII Div 1/2; ASME II-D; EN 13445; API 510.