Why does OD differ from some catalog 174.6 mm values?

This app uses the B16.5 raised-face diameter stored in flangeDimension.json (NPS 4 Class 150 RF OD = 157.2 mm) with B36 pipe OD as ID — the same proxy used by the flange gasket stress tool.

When is full face required?

When both flanges are flat face or the specification requires a full-face gasket. Bolt holes follow the B16.5 pitch circle for the selected NPS/class.

Does soft rubber report Wm2 = 0?

Yes. App. 2 soft elastomer uses y ≈ 0, so Wm2 = 0. Operating load still uses m in Wm1.

Non-Metallic Flat Gasket Dimensions & Sealing Area Calculator (ASME B16.21)

1. Core Formula & Variable Definitions

ASME B16.21 Nonmetallic Flat Gaskets for Pipe Flanges · ASME B16.5 Pipe Flanges and Flanged Fittings · ASME BPVC Section VIII Division 1 Appendix 2 · ASME B36.10M / B36.19M pipe outside diameter

A_g = π/4 · (d_o² − d_i²)

W_m2 = A_g · y · W_m1 = π/4 · G²·P + 2π·b·G·m·P

IBC: d_o = B16.5 raised-face OD · d_i = B36 pipe OD · Full face: d_o = flange OD

Default NPS 4 · 150 · IBCOD × ID 157.2 × 114.3 mmWm2 100.9 kNy 1600 psi

Geometry from ASME B16.5 flangeDimension.json (not a separate invented B16.21 numeric table). Effective width b follows VIII-1 App. 2 (inch basis). Soft rubber y = 0 → Wm2 = 0. B16.47 NPS 26–60 out of Phase-1.

d_o (Gasket outer diameter) — IBC: B16.5 raised-face diameter. Full face: flange outside diameter.
d_i (Gasket inner diameter) — ASME B36 pipe outside diameter for the NPS.
A_g (Gasket contact area) — π/4 · (d_o² − d_i²).
y (Minimum seating stress) — VIII-1 App. 2 Table 2-5.1 style seating stress.
m (Gasket factor) — VIII-1 App. 2 maintenance factor for operating load Wm1.
W_m2 (Minimum seating load) — A_g · y — assembly seating requirement.

2. Screening Assumptions

B16.5 NPS ½–24 Class 150–900 IBC/FF geometry with VIII-1 App. 2 Wm1/Wm2. Not a substitute for OEM crush or creep data.

Default dutyNPS 4 · Class 150 · IBC · compressed elastomer · 1.5 mm · 10 bar

Hero OD × ID = 157.2 × 114.3 mm; Wm2 ≈ 100.9 kN from B16.5 RF OD × B36 pipe OD and App. 2 y.

IBC geometryRF OD × pipe OD

Matches flange-gasket-stress sheet proxy from flangeDimension.json.

Full-face geometryFlange OD × pipe OD + B16.5 BCD/holes

Bolt pattern 100% from B16.5 drilling fields in the same table.

Out of scopeB16.47 Series A/B · spiral-wound/RTJ · OEM cold-flow curves

Use gasket-dimension-selection for B16.20 metal gaskets.

Quick Reference Lookup Table

Class 150 IBC ring — compressed elastomer (y = 1600 psi) · OD/ID from B16.5 RF × B36 OD
NPS	OD (mm)	ID (mm)	Wm2 (kN)
2	91.9	60.3	41.7
3	127.0	88.9	71.3
4	157.2	114.3	100.9
6	215.9	168.3	158.5
8	269.9	219.1	215.2
10	323.8	273.0	262.7
12	381.0	323.8	349.3

Wm2 uses App. 2 y for compressed elastomer sheet. Confirm OEM B16.21 charts and facing (RF vs FF) before procurement.

3. Gasket Material & Code Limits

m and y follow ASME VIII-1 Appendix 2 Table 2-5.1 style screening values used elsewhere in FieldEngineersKit.

Material Group	Temperature Range	Allowable Stress / Limit	Engineering Notes
Compressed elastomer sheet (non-asbestos)	≈ 200 °C screening	m = 2.0 · y = 1600 psi	Default CAF/NA sheet factors.
PTFE / ePTFE sheet	≈ 260 °C screening	m = 2.0 · y = 1600 psi	Cold flow under Class 600+ — prefer SWG with rings.
Flexible graphite sheet	≈ 450 °C screening	m = 2.0 · y = 900 psi	App. 2 flexible graphite sheet seating factors.
Neoprene / soft rubber	≈ 80 °C screening	m = 0.5 · y = 0 psi	Soft elastomer — Wm2 = 0; sealing relies on elastomer contact, not App. 2 y.

Code Applicability & Safety Boundaries

Screening only — confirm OEM B16.21 dimensional charts
B16.47 large-diameter flanges not in Phase-1 extract

4. Step-by-Step Worked Example

Field VerificationShow

Worked example — NPS 4 Class 150 IBC compressed elastomer

Select an ASME B16.21-style IBC ring gasket for NPS 4 Class 150 RF flanges in compressed non-asbestos sheet, 1.5 mm thick, design pressure 10 bar.

NPS / Class:4 / 150Profile:IBC ringMaterial:Compressed elastomer · m = 2 · y = 1600 psiP:10 bar

1

Lookup geometry

d_o = RF OD from B16.5; d_i = B36 pipe OD

Result:d_o = 157.2 mm · d_i = 114.3 mm

2

Contact area

A_g = π/4 · (d_o² − d_i²)

Result:A_g ≈ 9148 mm² (91.5 cm²)

3

Seating load Wm2

W_m2 = A_g · y

Result:W_m2 ≈ 100.9 kN

Conclusion: Screening dimensions are 157.2 × 114.3 mm with Wm2 ≈ 100.9 kN. Carry NPS/class to flange dimension and PCC-1 torque tools; confirm OEM B16.21 charts before PO.

5. How to look up B16.21 flat gasket dimensions

1
Select NPS and class
Choose the mating flange NPS and pressure class (B16.5 Phase-1).
2
Choose IBC or full face
IBC for raised-face rings; full face when both flanges are flat face or FF gasket is specified.
3
Pick material and thickness
Sheet material sets App. 2 m and y. Thickness is recorded for procurement (area loads use face geometry).
4
Read OD × ID and Wm2
Hero shows OD × ID. Badges show Wm2 and m·y. Export CSV/PDF or carry size/class to related flange and bolt tools.

6. Frequently Asked Questions & Technical References

Show

A field lookup of nonmetallic sheet gasket OD/ID for ASME B16.5 flanges, plus VIII-1 Appendix 2 Wm2 seating load from contact area and y.