Engineering guide
The 2505 module calculates flange connections to DIN 2505 in the 1990 draft edition. This German flange design standard has been withdrawn and was never published as a final edition; its calculation rules, however, were for decades the standard method for flange calculations in German equipment engineering and live on in substance in the German AD 2000 code, Merkblätter B 7/B 8, and – with an extended tightness concept – in DIN EN 1591-1. For re-assessing existing equipment designed on the basis of DIN 2505, and for comparative calculations, the method remains relevant.
The DIN 2505 calculation is a force and moment verification: from the internal pressure, the gasket loads in the seating and operating conditions, and the moment arms to the bolt circle, the flange moments are formed and set against the section moduli of the flange cross-section. The usual configurations are covered – welding neck flange with a tapered hub, plain slip-on welded flange, and loose (lapped) flanges – whose load-bearing behaviour is captured differently through the tapered hub or the effective contribution of the pipe.
In practice this calculation is needed when custom flanges outside the standardized pressure ratings are to be designed, when existing flanges must be re-rated for changed operating conditions, or when a gasket change has to be evaluated – the gasket parameters enter directly into the required bolt loads and thus into the flange moments.
Scope
- Flanges
Typical workflow
Define configuration and geometry
The flange type (welding neck flange with tapered hub, plain welded flange, loose flange), flange ring thickness, inside and outside diameter, bolt circle and number of bolts are recorded; for the welding neck flange additionally the dimensions of the hub.
Determine gasket parameters and bolt loads
From the gasket parameters for the seating and operating conditions follow the required gasket loads; together with the hydrostatic end force from the internal pressure, these yield the required bolt loads for both conditions.
Form moment arms and flange moments
Pressure force, gasket load and pipe force act with different moment arms relative to the bolt circle. For the seating condition and the operating condition, the resulting flange moment is formed; the more unfavourable case governs.
Determine the section modulus of the flange cross-section
The section modulus of the load-bearing cross-section – flange ring with the contributing pipe or hub portion, weakened by the bolt holes – is calculated; for the welding neck flange, the hub geometry enters decisively.
Perform the stress check
The flange stress resulting from moment and section modulus is compared, for both conditions, with the allowable values of the flange material at the associated temperature; in parallel, the bolt check is performed (module 250S).
Frequently asked questions
Why did DIN 2505 never progress beyond draft status, and what applies today?
The 1990 draft was overtaken by European standardization: for flange calculations with a tightness verification, DIN EN 1591-1 applies today, and in pressure vessel design alternatively AD 2000 B 7/B 8 or EN 13445-3. The DIN 2505 draft was nevertheless the accepted engineering practice for decades; many existing units and the old gasket parameters (k₀·K_D, k₁) are based on it.
How does DIN 2505 fundamentally differ from EN 1591-1?
DIN 2505 is a pure strength verification with separate load cases for seating and operation and lump-sum gasket parameters. EN 1591-1, by contrast, treats the joint as an elastic overall system of flange, bolts and gasket with stiffnesses and leak-rate-based gasket parameters, and thereby also provides a reliable statement on tightness and on the required assembly bolt load. The results of the two methods can differ considerably.
Which load case typically governs for the flange?
That depends on the gasket: soft gaskets with a low seating load usually make the operating condition governing, hard metallic gaskets with a high seating stress often the seating condition without internal pressure. Both conditions must therefore always be calculated – a verification for the operating pressure alone is incomplete.
Can I also use the method to re-rate standardized flanges per DIN EN 1092-1?
Yes, that is a frequent application: standardized flanges are covered by their pressure-temperature ratings only for standard conditions. With unusual gaskets, additional forces from the piping, or temperatures outside the tabulated values, the calculation provides the confirmation – or shows that a higher pressure rating is required.
Technical content source: LV-Solved-Problems-Content 628d313247e7