Engineering task and calculation objective
Without reliable gasket factors, no flanged joint can be designed seriously: the factors determine what surface pressure the gasket needs at bolting-up for seating and what residual pressure is required in operation for tightness — and thus directly govern the minimum bolt loads to AD 2000 B7 (the German pressure vessel code) and the flange moments to B8. Anyone who wants to determine or compare gasket factors needs them consistently in the correct parameter system.
The DICH module provides a library of common standard gaskets — from soft-material and rubber gaskets through PTFE and graphite to metallic and spiral-wound gaskets — and additionally allows manual input of a special gasket from the manufacturer's data sheet. For each gasket, the parameters of the AD 2000 system are output (seating and operating factors to Merkblatt B7); in parallel, the module calculates the corresponding factors to the ASME standard (gasket factor m and minimum seating stress y), so that the same gasket can also be used in a calculation to ASME VIII.
DICH thus acts as the central source of gasket data for the joint modules: the selected values flow directly into the bolt calculation (B7), the flange calculation (B8) and bolted plates with a peripheral moment (B5, B51C). This avoids transcription errors and ensures that the bolting-up and operating conditions are assessed with the same gasket data.
Standard and calculation basis: AD 2000 B7 & ASME VIII
Calculation workflow
- Select the gasket type: The gasket type is chosen from the built-in table — for example a soft-material gasket, PTFE, graphite, a metal-soft-material combination or a metallic gasket. Alternatively, a special gasket is entered manually with the parameters from the manufacturer's data sheet.
- Define the dimensions: Inside and outside diameter or the effective gasket width are entered; from these follow the compressed area and the effective diameters to which the factors and, later, the force calculations refer.
- Provide the AD factors: For the selected gasket, the module supplies the factors to AD 2000 B7 for the bolting-up condition (required seating deformation) and the operating condition (pressure-dependent minimum surface pressure), each referred to the relevant temperatures.
- Calculate the ASME factors in parallel: At the same time, the factors to the ASME standard are determined: the gasket factor m for the operating condition and the minimum seating stress y for seating the gasket. This makes AD and ASME calculations possible with consistent gasket data.
- Pass the factors to the joint calculation: The factors are passed to the modules B7 (minimum bolt loads), B8 (flange ring thickness) and B5/B51C (plates with a peripheral moment), where they enter the force and moment calculations of the individual conditions.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Gasket width | bD | mm |
| Mean gasket diameter | dD | mm |
| Minimum seating stress | σVU | N/mm² |
| Area | AD | mm² |
| Lower gasket seating load | FDVU | N |
| Gasket factor | m | - |
| Characteristic gasket value | k1 | mm |
| Characteristic gasket value | k0·kD | N/mm |
| Gasket height | hD | mm |
| Number of combs | n | - |
| b | b | in |
| G | G | in |
| y | y | psi |
| a | A | in² |
| (g.-seat.)W_m2 | Wm2 | lbf |
| m | m | - |
| k1 | k1 | in |
| k0kD | k0·kD | lbf/in |
| h_D | hD | in |
| n | n | - |
Frequently asked questions
How do the gasket factors to AD 2000 differ from those to ASME?
Both systems describe the same physical behavior with different quantities: AD 2000 B7 works with factors for the seating deformation at bolting-up and the pressure-dependent minimum surface pressure in operation; ASME VIII uses the dimensionless gasket factor m and the seating stress y. The values cannot be converted directly into one another, since the methods use different effective widths and safety philosophies — which is why the module outputs both parameter sets separately.
When should I use manufacturer data instead of the table values?
The built-in standard values are typical parameters for the respective gasket class. Modern gaskets — especially graphite and PTFE composite gaskets — can deviate from them considerably. As soon as tightness requirements become specific (TA Luft, a defined leakage rate) or the joint is marginally sized, verified manufacturer data should be used via manual input.
Why is the gasket width so important for the result?
The factors are surface pressures: the required force is the pressure times the compressed area. A wider gasket increases the required bolting-up force proportionally without necessarily improving tightness. Excessively wide soft gaskets are a classic cause of overloaded bolts and flanges — narrower gaskets or grooved (camprofile) types defuse the problem.
Do the factors also apply at elevated temperature?
Only to a limited extent. Soft-material and PTFE gaskets relax with rising temperature, causing the surface pressure in operation to drop; each gasket type has temperature limits for its use. At high temperatures, creep and relaxation behavior should be checked against the manufacturer's data, and gaskets with metallic support should be chosen if necessary.