BIZOMAT MAKEOS · Strength
Pressure Vessel Shell and Head Thickness Comparison
What wall thickness does this vessel shell need, and how do hemispherical, ellipsoidal and torispherical heads compare?
Required thickness of a cylindrical shell under internal pressure and of hemispherical, 2:1 ellipsoidal and torispherical heads by the widely used ASME Section VIII Division 1 formulas, with joint efficiency and corrosion allowance, compared side by side, plus the hydrostatic test pressure — for preliminary comparison only.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Design pressure | MPa | Internal design pressure. |
| Inside diameter | mm | Inside diameter of the shell. |
| Allowable stress at design temperature | MPa | Allowable tensile stress of the plate at design temperature (from the code’s material tables). |
| Joint efficiency | Weld joint efficiency for the radiography extent (1.0 full, 0.85 spot, 0.7 none for butt welds). | |
| Corrosion allowance | mm | Corrosion allowance added to the calculated thickness. |
| Hydrotest factor | Hydrostatic test pressure as a multiple of design pressure (code-dependent; also adjusted by the stress ratio). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Design pressure
- What it is
- Internal design pressure of the vessel, as set for its design under the applicable pressure equipment code.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 100 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- MPa, not bar: 1 MPa = 10 bar.
What this means: Inside diameter
- What it is
- Inside diameter of the cylindrical shell; the heads are taken to have the same inside diameter.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Allowable stress at design temperature
- What it is
- Allowable tensile stress of the plate material at design temperature, from the pressure vessel code’s material tables.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 138 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Joint efficiency
- What it is
- Weld joint efficiency for the joint type and extent of radiography, from the pressure vessel code.
- Units and format
- Enter a plain number with no unit. The form accepts 0.3 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.85 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Enter a fraction, not a percentage.
What this means: Corrosion allowance
- What it is
- Extra thickness added to every calculated thickness to allow for metal lost to corrosion or erosion over the vessel’s life.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Added directly to each thickness.
What this means: Hydrotest factor
- What it is
- Hydrostatic test pressure as a multiple of the design pressure, from the applicable code.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.3 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Test pressure = factor × design pressure.
Method and formulas
- Cylinder (circumferential stress): t = p R ÷ (S E − 0.6p) + CA.
- Hemispherical head: t = p R ÷ (2 S E − 0.2p) + CA.
- 2:1 ellipsoidal head: t = p D ÷ (2 S E − 0.2p) + CA.
- Torispherical head (crown radius = D, knuckle 6% D): t = 0.885 p L ÷ (S E − 0.1p) + CA.
- Example: 1 MPa in a 1000 mm shell needs 5.7845 mm; a 2:1 head needs 5.7662 mm.
Limitations
- Preliminary comparison only; pressure vessels must be designed, fabricated, inspected and certified to the applicable code (AS 1210, ASME VIII, EN 13445).
- External pressure, nozzles, supports and local loads are not covered.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Compare head types for weight and cost
- Estimate plate thickness before detailed design
- Check a vessel’s nominal wall against its pressure
Who it is for
- Mechanical engineers
- Process engineers
- Estimators
What you get
- Shell thickness
- Head thickness for three types
- Hydrostatic test pressure
Interpreting the result
- Hemispherical heads are thinnest but cost most to form; torispherical heads are cheapest but thickest.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 290–294. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Explains the concept · BIZOMAT original book
Remaining life and inspection intervals
In Ultrasonic Testing by the Numbers
What it covers: From survey readings to a decision: minimum required thickness for pipe and vessel shells, corrosion rate, remaining life, its uncertainty, the next inspection date and when to repair or replace.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Pressure Vessel Shell and Head Thickness Comparison calculator