Engineering task and calculation objective
The AFLT module provides the dimensions of forged flanges to ASME B16.5 — the governing standard for piping flanges from NPS 1/2 to NPS 24 in pressure classes 150 through 2500. Instead of a strength calculation, the module delivers the standardized geometry data: outside diameter, bolt circle diameter, number of bolts, diameter of bolt holes, core and stress cross-sections, and bolt lengths, depending on nominal pipe size, pressure class, schedule, and flange type (welding neck, slip-on, threaded, lap joint, blind flange).
In addition, the gasket quantities needed for a subsequent flange calculation per Appendix 2 are prepared: mean contact diameter, basic seating width, effective seating width, and the load reaction diameter of the gasket face. AFLT thus serves as the data source for reassessing standardized flanges under loads that go beyond the pressure-temperature rating — for example under external piping forces and moments.
The module is used in piping and pressure vessel engineering in every specification of ASME flange connections: for bills of material, bolt procurement, gasket selection, and as the geometric basis for further verifications.
Standard and calculation basis: ASME B16.5
Calculation workflow
- Select nominal pipe size and pressure class: The starting point is the nominal pipe size (NPS) and the pressure class (Class 150–2500). Together with the material group, ASME B16.5 determines via the pressure-temperature ratings whether the class is adequate for the pressure and temperature of the application.
- Define flange type and schedule: The flange type (welding neck, slip-on, threaded, lap joint, blind) and the pipe schedule determine the bore and hub geometry. For a welding neck flange, the hub bore must match the connected pipe so that the weld is flush on the root side.
- Output flange and bolt data: The module delivers the outside diameter, bolt circle diameter, number of bolts, diameter of bolt holes, core diameter, and bolt length for the selected combination — the complete basis for procurement and assembly.
- Derive the gasket parameters: From the inside and outside diameter of the gasket face, the mean contact diameter, the basic seating width b₀, the effective seating width b, and the load reaction diameter G of the gasket face are determined — the input quantities for a flange calculation per ASME VIII-1, Appendix 2.
Input quantities
| Quantity | Symbol | Unit |
|---|---|---|
| Schedule | (150, 300, ..., 2500) psi | psi |
| Flange Type | Flanschtyp | – |
| Pipe size | (0.5, 0.75, ..., 24) in | in |
| Outside diameter | O in | in |
| Thickness of flange | Q in | in |
| Raised face diameter | R in | in |
| Hub base diameter | X in | in |
| Length thru hub | Y in | in |
| Min. thread length **) | T in | in |
| Diameter of bore **) | W, B, J in | in |
| Bevel hub diameter | H in | in |
| Radius of fillet | r in | in |
| Bolt circle diameter | in | in |
| Number of bolts | Schrauben | – |
| Outside diameter | in | in |
| Diameter of bolt holes | in | in |
| Bolt length | in | in |
| Approximate weight (if available) | Gewicht | lb |
| Outside diameter | O in | mm |
| Thickness of flange | Q in | mm |
| Raised face diameter | R in | mm |
| Hub base diameter | X in | mm |
| Length thru hub | Y in | mm |
| Min. thread length **) | T in | mm |
Frequently asked questions
Does a flange to ASME B16.5 need to be calculated at all?
Within the pressure-temperature ratings, the standardized flange is considered verified — an individual calculation is not required. A reassessment (e.g., per Appendix 2) becomes necessary when significant external forces and moments from the piping act on the joint, when special gaskets with a high seating load are used, or when cyclic loading is present. AFLT provides the geometry data for that.
Where does the scope of ASME B16.5 end?
B16.5 covers NPS 1/2 to NPS 24. Larger flanges from NPS 26 upward are governed by ASME B16.47 (Series A formerly MSS SP-44, Series B formerly API 605) with, in part, markedly different bolt circles and bolt counts. The two standards are not compatible — a Series B flange does not mate with a Series A counterpart of the same nominal size.
What should be considered for the bolt length?
The bolt length from the standard applies to the standard combination of two flanges of the same class with raised face and standard gasket. Additional elements — washers, thicker gaskets, spectacle blinds, wafer-type valve bodies — increase the required grip length. As a rule of thumb, at least two to three threads should protrude beyond the nut after assembly.
What distinguishes welding neck and slip-on flanges in application?
The welding neck flange is butt-welded to the pipe, carries the full pipe cross-section through, and is the first choice for high pressures, cyclic loading, and low temperatures. The slip-on flange is easier to assemble and cheaper, but has two fillet welds, lower fatigue strength, and is usually used only up to moderate pressure classes and for non-critical media.