Sealing Elements for Flanged Joints
Gaskets are the critical sealing component in every bolted flange connection. A correctly specified gasket prevents leakage across the full range of operating pressure, temperature, and chemical conditions while accommodating flange surface imperfections and thermal cycling.
Gasket Types for ASME Flanges
| Type | Standard | Construction | Best For |
|---|---|---|---|
| Spiral Wound | ASME B16.20 | Alternating V-shaped metal winding + soft filler. Outer guide ring + inner ring | The workhorse gasket. All process services, wide P/T range |
| Ring Type Joint (RTJ) | ASME B16.20, API 6A | Solid metal ring. Octagonal (R-type) or oval | High pressure, high temperature, critical service, wellheads |
| Kammprofile / Grooved Metal | ASME B16.20 | Serrated metal core with soft facing layer on both sides | Heat exchangers, large vessels, where spiral wound not suitable |
| Jacketed | ASME B16.20 | Soft filler fully or partially enclosed in metal jacket | Heat exchangers, wide temperature range |
| Corrugated Metal (CMG) | — | Corrugated metal ring with soft facing | Low seating stress applications |
| Non-Metallic (Cut / Sheet) | ASME B16.21 | Compressed fiber, PTFE, flexible graphite without metal reinforcement | Low pressure, non-critical, large diameters |
| Double-Jacketed | ASME B16.20 | Soft filler completely enclosed in two-piece metal jacket | Heat exchangers, pumps, valves |
| PTFE Envelope | — | PTFE envelope around elastomer or fiber core | Strong chemicals, where metal contamination prohibited |
| Insulation Gasket | — | Gasket with isolation sleeve and washer | Electrical isolation of flanges (CP systems) |
Spiral Wound Gasket Components
| Component | Material Options | Function |
|---|---|---|
| Metal Winding | 304, 316L, 321, 347, Duplex, Inconel 600/625, Monel 400, Titanium | Provides structural strength and resilience |
| Filler Material | Flexible Graphite, PTFE, Mica, Phlogopite | Provides sealability. Graphite for high temp, PTFE for chemical |
| Outer Guide Ring | Carbon Steel (painted), 304 SS, 316 SS | Centering. Prevents over-compression |
| Inner Ring | 304 SS, 316 SS, Duplex, Inconel | Prevents filler erosion, protects against corrosion, heat shield |
Spiral Wound Color Coding (Per ASME B16.20):
- Outer ring color identifies metal winding material
- Filler stripe color identifies filler type
RTJ Gasket Types
| Type | Standard | Cross-Section | Application |
|---|---|---|---|
| Type R Oval | ASME B16.20 | Oval | Standard ASME RTJ flanges. Original design. Reusable limited times |
| Type R Octagonal | ASME B16.20 | Octagonal | Modern standard. Better sealing. Not reusable after compression |
| Type RX | API 6A | Pressure-energized octagonal | API 6B flanges, wellheads, some ASME sizes |
| Type BX | API 6A | Octagonal with beveled corners | API 6BX flanges, high-pressure wellheads, subsea |
RTJ Material & Hardness:
| Material | Maximum Hardness (HRB) | Application |
|---|---|---|
| Soft Iron | 56 | General sweet service. Softer than flange groove |
| Low Carbon Steel | 68 | General service |
| 4-6% Chrome / 1/2% Moly | 86 | Moderate temperature |
| 304 SS | 83 | Corrosive, moderate temp |
| 316 SS | 83 | Corrosive, chlorides, sour |
| 347 SS | 83 | High temperature (stabilized) |
| Inconel 825 | 92 | Sour, acid, high chloride |
| Inconel 625 | 99 | Sour HPHT, extreme corrosion |