Engineering task and calculation objective
Module AUZY calculates openings and branches in cylindrical shells to DIN EN 12952-3, the design standard for water-tube boilers and installation components. The user chooses among seven configurations: unreinforced isolated openings, perpendicular branches, reinforced openings with an oblique branch, non-radially arranged branches, Y-shaped branches, forged fittings, and adjacent openings and branches whose reinforcement zones interact.
To calculate openings in cylindrical shells to DIN EN 12952-3 means performing the ligament (weakening) verification via the pressure-area method: the pressure-loaded area is compared with the load-bearing cross-sectional areas of shell, branch and, where applicable, reinforcement. From this the module determines the required wall thicknesses for the cylindrical shell and the branch as well as the allowable internal pressure of the weakened shell.
The material properties are taken from the database; the allowable stress is determined per clause 6 of DIN EN 12952-3 with the appropriate safety factor. Figures illustrating the geometric input quantities and an overview of the calculation basis are provided in the module — typical for boiler drums, headers and distributors in steam generator engineering.
Standard and calculation basis: DIN EN 12952-3/8: 2023-01
Calculation scope
- Unreinforced openings in cylindrical shells
- Single openings with vertical branches in cylindrical shells
- Reinforced openings with oblique nozzle in cylindrical shells
- Non-radial branches in cylindrical shells
- Y-shaped branches in cylindrical shells
- Forged integral branches in cylindrical shells
- Adjacent openings and branches in cylindrical shells
Calculation workflow
- Select configuration: The applicable configuration is chosen from the seven available — from the unreinforced isolated opening through oblique, non-radial and Y-shaped branches to forged fittings and adjacent openings.
- Enter geometry and materials: Diameters and wall thicknesses of the main shell and the branch, as well as the distances between adjacent openings, are entered; the strength values of both components come from the material database, and the allowable stress follows per clause 6 of the standard with the corresponding safety factor.
- Calculate required base wall thicknesses: For the unweakened cylindrical shell and for the branch, the required wall thicknesses under internal pressure are determined first — they are the reference for the weakening verification.
- Perform the pressure-area comparison: At the opening, the pressure-loaded area and the load-bearing material cross-sections of shell, branch and reinforcement are balanced. For adjacent openings, the load-bearing ligament between the openings is verified in addition.
- Report the allowable pressure: The area comparison yields the allowable internal pressure of the weakened shell; it is compared with the design pressure and immediately shows whether reinforcement (a thicker branch, a reinforcing plate, a forged fitting) is required.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Design pressure | Pc | bar |
| Design pressure | pc | N/mm² |
| Reference temperature | tor | °C |
| Temperature tolerance | tz | °C |
| Design temperature | tc | °C |
| Material | Zylinders | - |
| Allowable stress | fs | N/mm² |
| Negative tolerance of wall thickness | c1 | mm |
| Corrosion allowance | c2 | mm |
| Outside diameter | dos | mm |
| Inside diameter | dis | mm |
| Allowable efficiency factor | νall | – |
| Common weakening factor | νm | – |
| Material | 1 | - |
| Allowable stress | fb | N/mm² |
| Negative tolerance of wall thickness | cb1 | mm |
| Corrosion allowance | cb2 | mm |
| Outside diameter | dob | mm |
| Inside diameter of branch | dib | mm |
| Material | 2 | - |
| Allowable stress | f | N/mm² |
| Negative tolerance of wall thick. | c1 | mm |
| Corrosion allowance | c2 | mm |
| Outside diameter | dob | mm |
Calculated results
| Quantity | Symbol | Unit |
|---|---|---|
| Design pressure | Pc | bar |
| Design pressure | pc | N/mm² |
| Reference temperature | tor | °C |
| Temperature tolerance | tz | °C |
| Design temperature | tc | °C |
| Material | Zylinders | - |
| Allowable stress | fs | N/mm² |
| Zuschl | ≥ max( , ) | mm |
| Negative tolerance of wall thickness | c1 | mm |
| Corrosion allowance | c2 | mm |
| Outside diameter | dos | mm |
| Inside diameter | dis | mm |
| Allowable efficiency factor | νall | – |
| Weakening factor | νb | – |
| Common weakening factor | νm | – |
| Efficiency factor | νb | – |
| Material | 1 | - |
| Allowable stress | fb | N/mm² |
| Negative tolerance of wall thickness | cb1 | mm |
| Corrosion allowance | cb2 | mm |
| Outside diameter | dob | mm |
| Inside diameter of branch | dib | mm |
| Material | 2 | - |
| Allowable stress | f | N/mm² |
Calculation options
Type
1. Openings according to section 8.1 bzw. 8.2 · 2. Single opening with vertical nozzle (8.3) · 3. Reinforced opening with oblique nozzle (8.3) · 4. Non-radial branch (8.3) · 5. Y-shaped branch (8.3) · 6. Forged Branch (8.3) · 7. Adjacent openings and nozzles (general) (8.3)
Frequently asked questions
When is an unreinforced opening permissible?
When the pressure-area comparison is satisfied without any additional reinforcement — which is achievable for small opening diameters relative to the shell diameter and a sufficient wall-thickness reserve in the main shell. As soon as the load-bearing cross-sections are no longer sufficient, reinforcement is needed via a thicker-walled branch, a forged fitting or a larger shell wall thickness.
What changes for oblique or non-radial branches?
For oblique and non-radially arranged branches, the opening in the shell is distorted into an ellipse; the larger opening dimension in the least favourable section plane governs. The standard also limits the permissible inclination angles. A common mistake is to calculate with the nominal diameter of the nozzle instead of the actual opening length in the section plane.
When must adjacent openings be considered together?
When the distance between two openings is smaller than the sum of their contributing lengths, the reinforcement zones overlap. The ligament between the openings must then carry the pressure load of both opening portions — the verification is performed for the ligament cross-section in the plane connecting the opening centres, including hole rows oblique to the axis.
Does the calculation apply only to boilers?
DIN EN 12952-3 is the water-tube boiler standard, but the pressure-area method is methodically related to that of EN 13445-3. For components within the scope of the boiler standard (drums, headers, distributors, boiler piping), AUZY is the appropriate module; for pressure vessels outside this scope, the opening rules of EN 13445-3 or AD 2000 B 9 apply.