🛡️ ASME Section VIII Vessel Calculator

Calculate the required thickness for cylindrical and spherical pressure vessels under internal pressure according to ASME Section VIII Div 1.

🛡️ ASME Section VIII Vessel Calculator

Calculate the required thickness for cylindrical and spherical pressure vessels under internal pressure according to ASME Section VIII Div 1.

Vessel Type

Inner Radius (R)

Allowable Stress (S)

Joint Efficiency (E)

✅ Calculation Result

Required Thickness (t)-mm

Vessel Cross-Section

P →

Cylindrical Shell

R = 500 mm

t = ? mm

Calculator Description

The ASME Section VIII vessel calculator applies the Boiler & Pressure Vessel Code Section VIII Div.1 to find the required wall thickness of cylindrical and spherical shells under internal pressure. It sets thickness so the hoop stress never exceeds the material's allowable stress and the vessel cannot burst.

What this calculator finds

Enter vessel shape (cylinder/sphere), design pressure P, inside radius R, allowable stress S and joint efficiency E to obtain the required thickness t.

Why it matters

Safe design of pressure vessels, storage tanks and heat-exchanger shells
Economic thickness selection based on material and joint efficiency
Re-rating and retrofit design of existing vessels

Formula

ASME Section VIII Div.1

The cylinder formula is based on hoop stress through the longitudinal weld; the sphere on uniform biaxial stress. The 0.6P / 0.2P terms in the denominator correct for thick walls.

\text{Cylinder:}\;\; t = \dfrac{P R}{S E - 0.6 P}

\text{Sphere:}\;\; t = \dfrac{P R}{2 S E - 0.2 P}

t — Required wall thickness [mm (Metric) or in (Imperial)]
P — Internal design pressure [MPa (Metric) or psi (Imperial)]
R — Inside radius [mm (Metric) or in (Imperial)]
S — Maximum allowable stress value [MPa (Metric) or psi (Imperial)]
E — Joint efficiency (0.1 ~ 1.0)

How the formula works

Higher P or R, or lower S or E, increases required thickness t.
Under the same conditions a sphere is thinner than a cylinder (the denominator is doubled).
If the denominator drops to zero or below (pressure far too high for the stress), the formula is invalid and no result is returned.

Worked example

Cylinder with P = 2.5 MPa, R = 500 mm, S = 138 MPa, E = 1.0: t = (2.5×500)/(138×1.0 − 0.6×2.5) = 1250/136.5 ≈ 9.16 mm. A sphere under the same conditions gives t = 1250/(2×138 − 0.2×2.5) = 1250/275.5 ≈ 4.54 mm.

Useful Tips

Practical tips

R is the inside radius — do not confuse it with the outside-diameter basis used in B31.3.
Take S from ASME II Part D by temperature and E from the joint-examination grade (progressive/full RT, etc.).
Heads (flat/elliptical/torispherical), flanges and nozzles use separate appendix formulas.

Limitations & cautions

Only internal-pressure hoop stress is covered; external-pressure buckling, supports, thermal and fatigue need separate checks.
Minimum-thickness and corrosion-allowance (CA) rules also apply, so add CA to the computed thickness.
Keep units consistent (Metric MPa·mm vs Imperial psi·in).