Blind Flange Calculator
Auto-select the PN class from EN 1092-1, calculate minimum thickness per EN 13445-3, and generate a matching 3D STEP model directly in the browser.
Open utilityWhat it does
Select a DN, set operating and test pressures, temperature, and material grade. The tool uses EN 1092-1 flange dimensions and EN 13445-3 stress checks to compute minimum thickness, recommend a standard plate thickness, and export a matching 3D STEP model for the active flange configuration.
When to use it (and when not to)
Use it when:
- You need a fast preliminary blind flange thickness for EN 13445 projects.
- You want an automatic PN lookup instead of manual table checks.
- You need a quick weight estimate for procurement or handling plans.
- You want a simple browser-side 3D STEP model for the current flange geometry.
Avoid it when:
- You need a fully certified calculation pack or third-party verification.
- Your material grade or flange standard is not covered in the dataset.
Inputs and outputs
Inputs
| Input | Description |
|---|---|
| DN | Nominal diameter for EN 1092-1 dimensions. |
| Operating pressure | Used to select the PN class. |
| Test pressure | Defaults from operating pressure but can be overridden. |
| Temperature | Used to pick temperature-dependent yield strength (deg C). |
| Material | P265GH, P355GH, or 1.4404 (316L). |
| Corrosion allowance | Added to the minimum thickness. |
Outputs
| Output | Format | Notes |
|---|---|---|
| Recommended thickness | mm | Rounded up to a standard plate list. |
| Minimum thickness | mm | From EN 13445-3 with corrosion allowance shown separately. |
| PN class and bolt data | On-screen | Includes bolt count, size, and bolt circle. |
| Weight estimate | kg | Based on flange OD, thickness, and material density. |
| 3D STEP model | STEP | Exports the configured blind flange body and bolt-hole pattern. |
How to use
- Choose DN and enter operating pressure.
- Confirm or override test pressure.
- Select temperature, material, and corrosion allowance.
- Read the recommended thickness, PN class, and bolt details.
- Use the STEP export action when you need a matching 3D model of the current flange geometry.
Example dataset: DN 100, operating pressure 10 bar, test pressure 14 bar, temperature 20 C, material P265GH, corrosion 1 mm.
- Expected output: Recommended thickness and PN class with bolt size and weight estimate.
Accuracy and verification
- The calculator is a preliminary sizing tool and does not replace full code verification.
- Confirm flange class selection against project pressure ratings and gasket requirements.
- Validate material properties, especially at elevated temperatures.
- EN 1092-1 high-pressure ratings (PN160+) are only standardized for a limited DN range; unsupported combinations show “No data”.
FAQ
- How is the PN class selected? The closest PN class that meets or exceeds the operating pressure is chosen from EN 1092-1.
- Can I override the test pressure? Yes. Editing the test pressure disables auto-updates.
- Which materials are included? P265GH, P355GH, and 1.4404 (316L) with temperature-dependent yield data.
- Does it upload my data? No. Everything runs locally in the browser.
- Is this a final design check? No. Use it for preliminary sizing and verify against your project specs.
Assumptions & standards
- Standards basis: Flange dimensions and PN class ratings are taken from EN 1092-1; the minimum thickness is calculated using the EN 13445-3 stress checks for blind flanges.
- Key assumptions:
- Static internal pressure loading only (operating and test cases).
- Uniform, temperature-dependent yield strength for the selected material grade (P265GH, P355GH, or 1.4404).
- Nominal EN 1092-1 flange dimensions without manufacturing tolerances.
- Corrosion allowance is added directly to the calculated minimum thickness as entered.
- Standard bolt pattern and gasket arrangement per the selected DN/PN combination.
- Limitations:
- Bolt loads, gasket seating stress, and flange rotation are not analyzed in detail.
- Fatigue, creep, and cyclic loading are not covered.
- External loads (piping moments, wind, seismic) are not considered.
- The result is not a certified code calculation and carries no code stamp.
- ⚠️ The Blind Flange Calculator provides preliminary sizing support. Results must be verified by a qualified engineer against the governing code edition and the project specification before manufacturing or purchase.
Why blind flange thickness scales the way it does
A blind flange is a flat circular plate with pressure on one face. Its governing equation, in every code, has the same shape:
t = C · D · √(P / f)
D is the effective diameter, P the design pressure, f the allowable
stress, and C a coefficient covering how the edge is held and how the gasket
loads it. The consequences of that square root are worth internalising:
- Doubling the pressure does not double the thickness — it multiplies it by √2 ≈ 1.41. Going from PN 10 to PN 40 (4×) multiplies thickness by 2, not 4.
- Diameter, by contrast, is linear. Doubling DN doubles the plate. Diameter is the expensive dimension, which is why large blinds get heavy so fast.
- Temperature enters through
f. A grade whose allowable stress halves at 400 °C needs √2 more thickness, even though nothing about the geometry changed.
There is a second requirement that often governs instead: the plate must also resist the gasket seating load from the bolts, applied before there is any pressure at all. For low-pressure, large-diameter flanges the seating case frequently sizes the plate, which is why a lightly loaded blind can still come out surprisingly thick.
Validation cases
The calculation engine is guarded by an automated test suite (59 unit tests); the cases below come directly from those tests, with reference values computed by hand from the closed-form equations. You can reproduce them in the calculator and compare digit for digit.
Case 1 — PN class selection (EN 1092-1 series)
The design pressure is mapped to the next standard PN class:
| Design pressure | Selected class |
|---|---|
| 10 bar | PN 10 |
| 12 bar | PN 16 |
| 40 bar | PN 40 |
| 41 bar | PN 63 |
| 321 bar | PN 400 |
Case 2 — flat circular plate bending (simply supported, uniform pressure)
Inputs: pressure P = 1.6 MPa (16 bar), effective radius R = 125 mm,
thickness t = 20 mm, E = 200 000 MPa, ν = 0.3.
Maximum bending stress (Roark / classical plate theory):
σ = 3·P·R²·(3 + ν) / (8·t²)
= 3 · 1.6 · 125² · 3.3 / (8 · 20²) = 77.34 MPa
Center deflection with plate stiffness D = E·t³ / (12·(1 − ν²)):
w = (5 + ν)·P·R⁴ / (64·D·(1 + ν)) = 0.170 mm
The engine's thickness solver is verified as the exact inverse of these equations: solving for the thickness that produces σ = 77.34 MPa returns t = 20 mm to 8 decimal places.
Case 3 — gasket seating bolt load
For an effective gasket diameter G = 250 mm, effective width b = 12 mm,
and seating stress y = 11 MPa (graphite class), the required seating load
follows the classical flange-bolting relation:
Wm1 = π·G·b·y = π · 250 · 12 · 11 ≈ 103 673 N
The bolting check then compares the provided stud area (count × stress area) against the largest of the seating, operating, and hydrotest requirements and reports which case governs.
These same numbers run as unit tests in the app's CI on every change — a release that breaks any of them cannot be deployed.
Related tools
Changelog
- Added browser-based 3D STEP export for configured blind flanges.
- Initial documentation.
Feedback / bug report
- Open a GitHub issue
- Email or DM with the slug
blind-flange-calculatorso we can reproduce the issue