FieldEngineersKitEngineering Reference & ASME Code Basis
1. Core Formula & Variable Definitions
ASME B16.20 (Metallic Gaskets for Pipe Flanges) · ASME B16.5 (flange facing / bolt-circle matching) · ASME PCC-1 (assembly / torque — separate calculator) · ASME VIII-1 Appendix 2 (m, y seating — reference only; not computed here)
Spiral-wound hero: ID × SEOD × OROD · also IROD
RTJ hero: Ring No. · P · w×h (octagonal R-series screening)
ASME B16.20 dimension lookup (this app) — seating Wm / torque → PCC-1 tool
This calculator looks up ASME B16.20 spiral-wound and RTJ ring dimensions from gasketDimension.json for NPS ½–24 and Class 150–1500. Spiral-wound hero is ID × sealing-element OD × outer-ring OD (inner-ring OD also shown). RTJ hero is ring number, pitch diameter P, and section w×h. It does not compute ASME VIII-1 Appendix 2 Wm1/Wm2 seating loads — use the bolt-torque (PCC-1) calculator for assembly targets. Confirm OEM datasheets before procurement.
- ID (Inner Diameter) — Spiral bore / RTJ ring ID from the lookup row (mm or in).
- IR_OD (Inner Ring OD) — Solid inner-ring outside diameter (spiral Style CGI screening).
- SE_OD (Sealing Element OD) — Active winding outside diameter (spiral).
- OR_OD (Outer / Centering Ring OD) — Guide ring OD — typically near the B16.5 bolt-circle envelope.
- P (RTJ Pitch Diameter) — Pitch diameter of the octagonal ring (mm or in).
- w × h (RTJ Section) — Ring width × height from B16.20.
- Ring No. (RTJ Ring Number) — R-series designation (e.g. R-37) — must match both flanges.
2. Allowances, Tolerances & Standards
Dimensions are screening lookups. Winding thickness, hardness, and fill material remain OEM / project items.
Common SWG winding compresses to the outer guide-ring thickness under target bolt load — not a calculator output.
B16.20 requires solid inner rings on Class ≥ 900, large NPS, and PTFE-filled spirals to stop inward buckling.
Outer ring sits inside the studs so the winding stays concentric during makeup.
Soft iron / SS rings must be softer than the flange groove so the ring yields, not the facing.
Quick Reference Lookup Table
| NPS | IR_OD (mm) | SE_OD (mm) | OR_OD (mm) | ID (mm) |
|---|---|---|---|---|
| 2" | 62 | 91.9 | 120.7 | 54 |
| 4" | 87 | 117.5 | 190.5 | 78 |
| 6" | 111.1 | 149.4 | 241.3 | 98.4 |
| 8" | 131 | 176 | 298.5 | 118 |
| 10" | 157.2 | 215.9 | 362 | 144.5 |
| 12" | 182.6 | 241.3 | 419.1 | 168.1 |
Values match data/piping/gasketDimension.json Class 150 spiral rows. NPS 4 OR_OD = 190.5 mm equals the Class 150 bolt circle. Live lookup also covers Classes 300–1500 and RTJ rings.
3. Material & Code Limitations
Material choice is project-driven. This tool only returns geometry for the selected type / NPS / class.
| Material Group | Temperature Range | Allowable Stress / Limit | Engineering Notes |
|---|---|---|---|
| 316L + Flexible Graphite (typical SWG) | Often to ~450 °C in air (higher in inert/steam — OEM) | Common m ≈ 3.0, y ≈ 69 MPa (reference) | Workhorse hydrocarbon / steam filler. Graphite oxidizes in air at high T. |
| 316L + PTFE filler | Typically ≤ ~260 °C | Lower y; inner ring required | Chemical service. Creep/relaxation risk — do not omit CGI inner ring. |
| RTJ Soft Iron / SS Octagonal | Per ring metallurgy | High-pressure Class ≥ 300 common | Ring number must match both grooved flanges (e.g. NPS 4 → R-37 in this app). |
| Reuse | N/A | Never reuse SWG / RTJ | Plastic set after makeup — PCC-1 prohibits reuse. |
Code Applicability & Safety Boundaries
- Calculator scope: B16.20 spiral and RTJ dimension lookup only. It does not solve Wm1/Wm2 or bolt torque.
- Carry NPS/class into flange dimension and PCC-1 torque tools after selecting the gasket.
- Confirm OEM winding ID / RTJ hardness against the mill certificate before PO.
4. Step-by-Step Worked Example
Field VerificationShowHide
Reproduce the app default: spiral-wound NPS 4 Class 150 from gasketDimension.json, then spot-check RTJ NPS 4 Class 300.
Select spiral-wound · NPS 4 · Class 150
Class must match the flange, not the pipe schedule.
Read ID, IR_OD, SE_OD, OR_OD
Hero shows ID × SE_OD × OR_OD = 78.000 × 117.500 × 190.500 mm.
Interpret outer ring
Field makeup uses the outer ring against the bolt circle.
Optional: Class 300 spiral
Outer ring follows the Class 300 bolt pattern.
Optional: RTJ NPS 4 Class 300
Ring number must match both RTJ flanges. Torque still uses the PCC-1 tool.
5. Frequently Asked Questions & Technical References
ShowHide
In this app table, OR_OD = 190.5 mm matches the B16.5 Class 150 NPS 4 bolt circle, so the centering ring sits inside the studs and keeps the winding concentric.
No. It is a B16.20 dimension lookup. For assembly targets use the PCC-1 bolt torque calculator (and project m/y values).
No. They take a permanent set on first makeup. ASME PCC-1 requires a new gasket after breakout.
Type R (octagonal/oval) is the B16.5 standard in this lookup. RX fits R grooves with pressure energizing. BX needs BX grooves (API 6A) and is not interchangeable with R.