EN 1092-1 Flange Rating Calculator
Check the Pressure Rating and Wall Thickness of EN 1092-1 Flanges
A flange is often the weakest pressure component in a piping system, and its ability to hold a given pressure depends on its type, the material, the temperature, and the available wall. Rather than computing the flange strength from first principles, EN 1092-1 provides standard dimension tables and rating tables that directly state the maximum allowable pressure for each flange type, material, and temperature.
This online calculator evaluates one or more flange types against those tables. For each requested flange type it determines whether the flange is standardized for the given nominal size, finds the maximum allowable pressure at the design temperature, and checks whether the available wall thickness is sufficient. It then reports the governing pressure rating and the utilisation across all of the requested types.
A Table-Based Method
This calculator is not a membrane-wall-thickness calculation. It works directly from the standard’s published tables:
- Dimension table — the standard geometry and minimum wall thicknesses for each nominal size (DN) and flange type
- Rating table — the maximum allowable pressure for each material, as a function of temperature (and, for non-austenitic materials, the forging dimension)
For each requested flange type the calculator performs a set of checks and, where allowed, reads the applicable pressure rating. If a check fails, that flange type is marked as not allowed (an X in the report) with a note explaining why, without stopping the evaluation of the other types.
The Checks for Each Flange Type
Standardization Limits
The first check confirms that the flange type is actually standardized for the given PN rating and nominal size. EN 1092-1 does not rate every combination of type, pressure class, and size. For example, a particular type may only be available up to a certain DN, or may not be rated at all for a given PN. If the combination is outside the standardized range, the type is marked not allowed and the reason is recorded.
Austenitic-Only Types
Types 35 and 37 are only permitted for use with austenitic materials. If one of these types is selected with a non-austenitic material, it is marked not allowed.
The VR Forging Dimension
For the non-austenitic flange types, the rating table is selected using the VR dimension, a characteristic forging/thickness size of the flange. After forging, at most 80% of this dimension can be machined away, so the VR value used for the table lookup is the standard forging dimension divided by 0.8:
The exact forging dimension depends on the flange type (for example C1 for Type 01, C2 for Type 11, and the largest of C1 or a type-specific dimension for the pressed collar types). For non-austenitic materials the VR value is used to select the correct row in the rating table; for austenitic materials there is only 1 row for each material.
Maximum Allowable Pressure at the Design Temperature
The rating table gives the maximum allowable pressure at a set of standard temperatures. The calculator linearly interpolates between the two temperatures that bracket the design temperature to find the pressure at the exact design temperature:
The room-temperature (RT) column covers the range from -10 °C to 50 °C and is treated as its upper end of 50 °C for interpolation: a design temperature of 50 °C or below takes the RT value directly, as shown in the formula:
If the design temperature exceeds the highest tabulated temperature for the material, the type is marked not allowed.
Required Wall Thickness
The calculator also checks that the available wall thickness is sufficient, accounting for the corrosion allowance. The required thickness depends on the flange type:
- Types 11, 21, and 34: based on the standard calculated thickness Sp11. For non-austenitic materials the Sp11 value already includes 1 mm of corrosion allowance, so it is subtracted again before adding the actual corrosion allowance:
For austenitic materials the included corrosion allowance is 0 mm, so the 1 mm is not subtracted:
- Type 01: based on the minimum wall thickness S01, which includes 1 mm of corrosion allowance
- Types 35, 36, and 37: based on the standard thickness for the type, with no corrosion allowance included
- Type 05 (blind flange): the initial thickness is based on the flange connection and cannot be evaluated directly; a corrosion allowance above the included 1 mm must be calculated separately
- Types 12, 13, and 32: no thickness effect on the flange, so no thickness check is applied
When the type-specific thickness value (for example S01) is not available for a given DN, the calculator substitutes the Sp11/S11 value and records a note. If no wall thickness is given, the type’s standard minimum wall thickness from the dimension table is used for the check.
Governing Rating and Utilisation
When several flange types are requested, the one with the lowest maximum allowable pressure is used for the code compliance check. The overall maximum allowable pressure is therefore the minimum of the allowed types, and the utilisation compares the design pressure to it:
where P_min is the governing (lowest) maximum allowable pressure among the allowed flange types.
The calculator evaluates the flange by comparing the design pressure to the governing maximum allowable pressure:
- Code Compliant (PASS): — the flange is rated for the design pressure at the design temperature
- Non-Compliant (FAIL): — the flange is not rated for the design conditions; a larger flange, a different type, a higher PN, or a different material is required
A utilisation of 80% means the flange is used at 80% of its pressure rating, leaving a 20% margin. Values above 100% indicate the flange is not rated for the design pressure.
Key Inputs
| Input | Description | Default |
|---|---|---|
| Nominal Size (DN) | Nominal diameter of the flange and pipe | From pipe selection |
| Wall Thickness | Nominal wall thickness of the connected pipe | From pipe selection |
| Design Pressure | Maximum internal pressure at operating temperature | User-defined |
| Design Temperature | Service temperature affecting the flange rating | User-defined |
| Corrosion Allowance | Thickness reserved for service-life material loss | 0 mm |
| Flange Type(s) | One or more EN 1092-1 flange types to evaluate | User-defined |
| Rating (PN) | Nominal pressure class of the flange | User-defined |
| Material | Material of the flange, from the EN 1092-1 rating table | User-defined |
The material must be one listed in the EN 1092-1 rating table for the calculation to proceed.
Supported Flange Types
The calculator supports the common EN 1092-1 flange types:
| Type | Description |
|---|---|
| 01 | Plate flange, for welding, for low pressure applications |
| 05 | Blind flange, for closing off a pipe flange |
| 11 | Weld neck flange, made from one piece for butt-welding to a pipe |
| 12 | Hubbed slip-on flange for welding using fillet welds |
| 13 | Hubbed threaded flange, for threading onto a pipe |
| 21 | Flange integral to equipment, similar in shape to Type 11 |
| 32+02 | Weld-on collar plate, used with a Type 02 loose plate flange |
| 34+04 | Weld neck collar, used with a Type 04 loose plate flange |
| 35+02 | Weld ring neck, used with a Type 02 loose plate flange |
| 36+02 | Pressed collar with long neck, used with a Type 02 loose plate flange |
| 37+02 | Pressed collar, used with a Type 02 loose plate flange |
Step-by-Step Calculation Process
The calculator performs the following steps for each flange type and pressure/temperature case:
- Locate the dimension row — Find the standard dimension row for the nominal size (DN)
- Locate the rating rows — Find the rating rows for the selected material
- Check standardization limits — Confirm the type is rated for the given PN and DN
- Check material restrictions — Confirm austenitic-only types are used with austenitic material
- Calculate the VR dimension — Determine the forging dimension and the table-lookup value
- Select the rating row — Choose the applicable row based on the VR value
- Interpolate the maximum allowable pressure — Find the pressure at the design temperature
- Check the required wall thickness — Apply the type-specific corrosion-allowance rule
- Determine the governing rating — Take the lowest maximum allowable pressure across the allowed types
- Evaluate utilisation and compliance — Compare the design pressure against the governing rating
Each step is documented in the calculation report with the applicable table values, formulas, and notes for full traceability.
Frequently Asked Questions
Why is the flange often the weakest point in a piping system?
Because the bolted connection is subject to more than just a simple longitudinal and circumferential membrane stress. There is preload, thermal expansion and gasket effects that all have an effect on the bolted connection. And even while a bolted connection does not have any yielding or breaking, it could deform enough so that the connection starts leaking. Flange leakages are one of the biggest sources of accidents in process systems.
What is the difference between a pressure rating and a maximum allowable pressure?
Pressure rating is an imaginary rating that is roughly designed for, while maximum allowable pressure is a rating for a specific material at a temperature and dimension.
What does the VR dimension represent?
The VR dimension is the forging reference thickness, as forgings get thicker, the minimum strength values tend to decrease. Because of this, the standards like EN10222 and A182 mention strength values together with a reference thickness.
Why is a blind flange (Type 05) not checked for wall thickness?
The blind flange has its corrosion allowance on the thickness of the flange because that is what corrodes. The problem is that apart from the standard included 1mm, there is no “minimum” thickness for the area exposed to the medium.
Is this calculator suitable for certification and documentation?
The calculator produces a detailed calculation report showing all input parameters, intermediate values, formulas applied, and code compliance status. The output is structured to support engineering documentation and design review. For formal certification, always verify results against the latest published version of the applicable standard.