Enter Design Inputs
Use consistent metric units. Allowable stress must come from the selected alloy, temper, weld condition, temperature, and applicable design standard.
Formula Used
This calculator applies common internal-pressure screening equations. Pressure and allowable stress are entered in MPa. Radius and thickness are entered in mm. That unit combination returns thickness in mm.
Cylindrical shell, hoop stress: t = PR / (SE − 0.6P)
Cylindrical shell, longitudinal stress: t = PR / (2SE + 0.4P)
Spherical shell: t = PR / (2SE − 0.2P)
| Symbol | Meaning | Unit |
|---|---|---|
| P | Internal design pressure | MPa |
| R | Inside radius | mm |
| S | Allowable stress at design temperature | MPa |
| E | Weld joint efficiency | decimal |
| t | Pressure-only required thickness | mm |
Nominal requirement = (pressure-only thickness + corrosion allowance) ÷ (1 − mill tolerance). This tool does not calculate external-pressure buckling or local-load effects.
How to Use This Calculator
- Choose a cylindrical or spherical shell.
- Enter the design pressure and inside diameter.
- Use the verified allowable stress for the exact aluminum condition.
- Enter a realistic weld efficiency, corrosion allowance, and mill tolerance.
- Add a proposed plate thickness to check its screening adequacy.
- Review the governing thickness and estimated MAWP.
- Export the result, then obtain a complete qualified design review.
Example Data
| Input | Example value | Why it matters |
|---|---|---|
| Geometry | Cylindrical shell | Determines the governing equation. |
| Design pressure | 1.20 MPa | Sets internal membrane loading. |
| Inside diameter | 1,000 mm | Defines the inside radius. |
| Allowable stress | 95 MPa | Must match alloy, condition, and temperature. |
| Joint efficiency | 0.85 | Accounts for welded seam performance. |
| Corrosion allowance | 1.00 mm | Reserves material for service loss. |
| Mill tolerance | 12.5% | Increases the nominal plate requirement. |
Aluminum Pressure Vessel Thickness Basics
Aluminum pressure vessels appear in transport, processing, aerospace, and laboratory systems. Their low density can reduce handling loads. Their corrosion resistance can also help in selected fluids. Yet aluminum does not remove design responsibility. Its allowable stress changes with alloy, temper, weld condition, and temperature. Use approved material data for the planned service temperature.
Stresses Created by Internal Pressure
Internal pressure creates two principal membrane stresses in a cylindrical shell. Hoop stress acts around the circumference. Longitudinal stress acts along the vessel axis. Hoop stress normally governs thickness because it is larger. A spherical shell shares stress in two directions. It can therefore require less wall thickness for the same diameter and pressure. Vessel geometry still needs careful review.
What the Calculator Evaluates
This calculator uses pressure, inside diameter, allowable stress, and weld efficiency. It then adds corrosion allowance. Mill tolerance increases the nominal plate requirement. The result is a screening thickness. The selected plate field checks whether a proposed nominal thickness remains adequate after tolerance and corrosion deductions. It also estimates an internal pressure limit from the governing equation.
Choosing Aluminum Material Values
Aluminum selection requires more than a single strength number. Common alloys behave differently after forming and welding. Heat affected zones can reduce useful strength. Elevated temperature can also reduce allowable stress. Choose the allowable stress from the governing design code and the correct material specification. Do not substitute yield strength unless the applicable method permits it. Use the lowest relevant design value.
Allowances and Weld Efficiency
Joint efficiency represents the expected strength of welded seams. It depends on weld category, examination level, and code rules. Do not assume one hundred percent efficiency. Corrosion allowance reflects anticipated metal loss during service. Some aluminum services need little allowance. Other environments can cause localized attack, crevice corrosion, or galvanic damage. Process chemistry matters more than a generic allowance.
Limits of This Screening Method
This page does not design heads, nozzles, flanges, supports, openings, or stiffeners. It does not evaluate vacuum, external pressure, buckling, fatigue, thermal cycling, seismic loads, wind loads, or pressure relief sizing. These cases can control the final design. Thick-wall behavior also needs more detailed analysis. A qualified engineer should complete the full calculation package before fabrication or operation.
Working With the Result
Start with consistent units. Enter pressure and allowable stress in megapascals. Enter dimensions in millimeters. Use the inside diameter at the required design condition. Enter a realistic weld efficiency and corrosion allowance. Provide a nominal plate thickness when checking an existing concept. Review the governing thickness and the adequacy message. Save the worksheet for project records, then confirm every assumption against current code requirements.
Early Mass Planning
Material density helps estimate shell mass. This supports lifting studies and transport planning. The estimate uses simple shell geometry. It excludes heads, nozzles, clips, insulation, paint, and weld buildup. Treat it as an early estimate only. Fabrication drawings require detailed weights. Consider material availability, forming limits, minimum code thickness, inspection access, drainage, and cleaning needs. These practical factors can alter the selected final thickness for service.
Frequently Asked Questions
1. What does this calculator determine?
It estimates required aluminum shell thickness for an internally pressurized cylinder or sphere. It includes pressure, inside diameter, allowable stress, weld efficiency, corrosion allowance, and mill tolerance. It also checks a proposed plate thickness when you enter one.
2. Why does a cylindrical shell need two checks?
Internal pressure produces hoop and longitudinal membrane stresses. Hoop stress commonly controls the required thickness. Both checks are shown because vessel geometry, input assumptions, and applicable rules still need verification.
3. Which allowable stress should I enter?
Use the allowable stress approved for the exact alloy, temper, product form, weld condition, and design temperature. Do not enter a generic tensile strength or yield strength unless the governing design method specifically requires it.
4. What is weld joint efficiency?
Joint efficiency accounts for the expected strength of a welded seam. It depends on the weld type, examination level, joint category, and the governing standard. Lower efficiency increases the required shell thickness.
5. Is corrosion allowance always needed for aluminum?
No. Some aluminum services have minimal general corrosion. However, localized corrosion, crevice attack, galvanic contact, and process contaminants may still matter. Select allowance using service chemistry, inspection strategy, and the applicable design basis.
6. Why does mill tolerance increase nominal thickness?
Plate can be supplied below its nominal ordered thickness within an allowed tolerance. Dividing by the remaining thickness factor helps ensure adequate material remains after tolerance and corrosion deductions.
7. What does the selected plate thickness check mean?
The check compares your proposed nominal plate against the calculator’s nominal screening requirement. It is not a fabrication release. A compliant vessel also needs complete code calculations, drawings, material control, welding procedures, inspection, and testing.
8. Can I use psi and inches?
Not directly in this version. Enter pressure and allowable stress in MPa. Enter all dimensions in mm. The equations are dimensionally consistent with those inputs and return thickness in mm.
9. How does temperature affect the result?
Temperature can reduce aluminum allowable stress and alter corrosion behavior. Use an allowable stress valid at the maximum design temperature. Review low-temperature toughness, process upset conditions, and thermal cycles separately.
10. Does it calculate heads, nozzles, or vacuum resistance?
No. Heads, openings, flanges, supports, external pressure, buckling, fatigue, seismic loads, and relief protection need separate methods. Any one of these can govern the final vessel design.
11. Can this result be used for fabrication?
No. Use it for preliminary studies and input checking only. Fabrication requires a qualified engineer’s calculation package, current applicable-code review, material traceability, approved weld procedures, inspections, pressure testing, and documented acceptance.