How to Order Gaskets
Gaskets seal the gap between flange faces under bolt load and internal pressure. A gasket ordered without its full specification, missing the winding material, filler type, ring number, or facing compatibility, will either arrive wrong or fail in service. A wrong color code on a spiral wound gasket means the wrong alloy was delivered. A missing inner ring on a large-diameter spiral wound gasket causes blowout under pressure.
This page covers the five major gasket families: spiral wound, ring joint, soft (non-metallic), kammprofile, and jacketed. Each section lists the mandatory attributes for a complete purchase order line item.
1. Spiral Wound Gaskets (ASME B16.20)
Spiral wound gaskets (SWG) consist of alternating plies of metal winding and soft filler material, wound into a spiral. They are the most common gasket type for raised face (RF) flanges in process piping.
Core Attributes
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Standard | ASME B16.20 | Always state the standard explicitly |
| 2 | Nominal size | NPS 1/2” through NPS 24” and above | Sizes above NPS 24” require an inner ring per ASME B16.20 |
| 3 | Pressure class | 150, 300, 600, 900, 1500, 2500 | Determines gasket OD, ID, and centering ring dimensions |
| 4 | Flange facing | Raised Face (RF) | RTJ flanges use ring joint gaskets, not spiral wound. Do not order SWG for RTJ flanges |
| 5 | Winding material | SS 304, SS 316L, Monel 400, Inconel 600, Hastelloy C-276 | Must match process corrosion requirements |
| 6 | Filler material | Flexible graphite (most common), PTFE (clean/chemical services), ceramic (high-temperature services above 550 °C) | Flexible graphite is the default for hydrocarbon and steam service; PTFE for oxidizing chemicals and food-grade applications |
| 7 | Inner ring | Required for NPS 24” and above, and for all Class 900 and above per ASME B16.20 | Material matches the winding material (e.g., SS 316L inner ring with SS 316L winding). Prevents inward buckling of windings under high bolt load |
| 8 | Outer ring (centering ring) | Carbon steel, painted per ASME B16.20 Table 3 color code | Centers the gasket on the flange and acts as a compression stop. Color identifies the winding/filler combination |
| 9 | Color coding | Per ASME B16.20 Table 3; see color code table below | Verify color code on delivery; wrong color = wrong material |
Color Coding (ASME B16.20 Table 3)
The outer (centering) ring is painted to identify the winding and filler material combination. This is a critical quality check at receiving inspection.
| Winding Material | Filler Material | Outer Ring Color |
|---|---|---|
| SS 304 | Flexible graphite | Yellow |
| SS 316L | Flexible graphite | Green |
| SS 321 | Flexible graphite | Turquoise |
| SS 347 | Flexible graphite | Blue |
| Monel 400 | Flexible graphite | Tan (light brown) |
| Inconel 600 | Flexible graphite | Orange |
| Hastelloy C-276 | Flexible graphite | Red |
| SS 304 | PTFE | Yellow with white stripe |
| SS 316L | PTFE | Green with white stripe |
2. Ring Joint Gaskets (ASME B16.20)
Ring joint gaskets (RJ or RTJ gaskets) are solid metal rings that seat into machined grooves on RTJ flanges. They are used for high-pressure and high-temperature services where a metal-to-metal seal is required.
Core Attributes
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Standard | ASME B16.20 (process piping), API 6A (wellhead and Christmas tree) | BX style rings are per API 6A only |
| 2 | Ring number | R or RX designation (e.g., R-24, R-35, RX-35) | Ring number is determined by flange size and pressure class per ASME B16.20 tables. Always state the ring number, not just the flange size |
| 3 | Style | R (standard), RX (pressure-energized), BX (API 6A, for 5K–20K rated pressures) | R-type is oval or octagonal cross-section. RX is pressure-energized (internal pressure increases sealing force). BX is for API 6A flanges in wellhead service |
| 4 | Cross-section | Oval or octagonal | Octagonal is preferred; it provides a higher contact stress and better sealing than oval. Oval is acceptable for older flanges with oval-only grooves |
| 5 | Material | Soft iron, low-carbon steel, SS 304, SS 316, Inconel 625, Monel 400 | The ring must always be softer than the flange groove material to ensure the ring deforms into the groove, not the flange |
| 6 | Surface finish | 63 µin (1.6 µm) Ra or better | Per ASME B16.20. Inspect rings on receipt for nicks, scratches, and tool marks; any surface defect will cause leakage |
3. Soft (Non-Metallic) Gaskets (ASME B16.21)
Soft gaskets are sheet-type, non-metallic gaskets used on flat face (FF) and raised face (RF) flanges in low-to-moderate pressure and temperature services. They are cut from sheet material to match the flange dimensions.
Core Attributes
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Standard | ASME B16.21 | Defines gasket dimensions (OD, ID) for standard flange sizes |
| 2 | Gasket material | Compressed non-asbestos fiber (CNAF), PTFE (virgin or filled), flexible graphite, rubber (EPDM, NBR, Viton/FKM) | CNAF is the general-purpose replacement for asbestos. PTFE for chemical services. Rubber for water, air, and low-pressure utility services |
| 3 | Dimensions | OD, ID, and thickness (in mm or inches) | Must match the flange facing dimensions per ASME B16.21 tables |
| 4 | Flange facing and gasket style | Flat Face (FF) flanges require full-face gaskets (with bolt holes). Raised Face (RF) flanges use ring-type gaskets (IBC/OBC dimensions, no bolt holes) | Using a ring-type gasket on a flat face flange causes uneven bolt load and risks flange cracking on cast iron flanges |
| 5 | Nominal size and class | NPS and pressure class of the mating flanges | Determines the OD and ID from ASME B16.21 tables |
| 6 | Thickness | 1.5 mm (1/16”), 3.0 mm (1/8”), or as specified | Thicker gaskets compress more but have higher blowout risk under pressure; use the minimum thickness adequate for the flange surface finish |
4. Kammprofile Gaskets
Kammprofile (also called “camprofile”) gaskets have a solid serrated metal core with a soft sealing layer bonded to both faces. They combine the strength of a metal gasket with the conformability of a soft facing, making them suitable for high-pressure and high-temperature services, heat exchangers, and applications with uneven flange surfaces.
Core Attributes
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Core material | SS 316L, Monel 400, Inconel 625, Hastelloy C-276 | The serrated metal core provides structural strength and recovery. Select based on process corrosion requirements |
| 2 | Sealing layer (facing) | Flexible graphite (standard), PTFE (chemical services) | The soft facing fills serration valleys and flange surface irregularities to create the seal |
| 3 | Nominal size | NPS or DN | Must match the flange dimensions |
| 4 | Pressure class | Per mating flange class | Determines gasket OD and ID |
| 5 | Flange standard | ASME B16.5, ASME B16.47, EN 1092-1 | State the flange standard so the gasket manufacturer can match dimensions |
| 6 | Outer guide ring | Carbon steel (centering function only) | The guide ring centers the gasket on the flange; it does not participate in sealing. Not always required; specify if needed |
5. Jacketed Gaskets
Jacketed gaskets consist of a soft filler material enclosed in a thin metal shell (jacket). The metal jacket provides blowout resistance and handling strength, while the filler conforms to flange surface irregularities. They are commonly used on heat exchangers, pressure vessels, and large-diameter equipment flanges.
Core Attributes
| # | Attribute | Values / Options | Notes |
|---|---|---|---|
| 1 | Jacket material | SS 304, SS 316L, Monel 400, Inconel 625 | The thin metal shell must resist process-side corrosion |
| 2 | Filler material | Flexible graphite (general service), ceramic fiber (high temperature), PTFE (chemical service) | Filler is enclosed within the metal jacket and provides the conformable sealing element |
| 3 | Style | Single jacketed (metal on one side only), double jacketed (metal shell on both sides, most common), French jacketed (double jacketed with an inner tail for self-centering) | Double jacketed is the standard style; specify single or French only when required by the equipment drawing or standard |
| 4 | Nominal size | NPS or DN, or exact OD/ID in mm | For non-standard equipment flanges, provide OD, ID, and thickness from the equipment drawing |
| 5 | Pressure class | Per mating flange or equipment spec | Determines required gasket dimensions |
| 6 | Flange standard | ASME B16.5, ASME B16.47, equipment-specific | For heat exchanger flanges, reference the equipment drawing number |
General Optional and Special Attributes
These attributes apply across all gasket types and should be included when the service or project specification demands it.
| Attribute | When Required | Details |
|---|---|---|
| NACE MR0175 / ISO 15156 | Sour service (H2S-containing environments) | Restricts metallic gasket materials (winding, ring, core, jacket) to NACE-compliant grades and conditions |
| Fire-safe rating | Hydrocarbon services, per client or regulatory requirement | Per API 6FB (fire test for end connections) or BS 7531 Grade X for sheet gaskets |
| Certificates | Almost always required | EN 10204 Type 3.1 (MTR) minimum. Include material composition, dimensional verification, and hardness (for metallic gaskets) |
| Color coding verification | Spiral wound gaskets | Verify outer ring color matches the specified winding/filler combination per ASME B16.20 Table 3 on receipt |
| Shelf life and storage | PTFE and rubber gaskets | PTFE has indefinite shelf life; rubber gaskets (EPDM, NBR, Viton) degrade over time. Specify storage conditions and maximum shelf life if required by project spec |
Example Line Items
Correct (Spiral Wound Gasket)
50 pcs - Spiral wound gasket, ASME B16.20, NPS 6, Class 300, RF, SS 316L winding, flexible graphite filler, CS outer ring, SS 316L inner ring, MTR EN 10204 3.1
This line item defines: quantity, gasket type, standard, size, class, facing, winding material, filler material, outer ring, inner ring, and certification.
Correct (Ring Joint Gasket)
24 pcs - Ring joint gasket, ASME B16.20, R-35, octagonal cross-section, SS 316, surface finish 63 µin Ra max, MTR EN 10204 3.1
Correct (Kammprofile Gasket)
12 pcs - Kammprofile gasket, NPS 10, Class 600, ASME B16.5 flanges, SS 316L core, flexible graphite facing, CS outer guide ring
Incorrect
50 - Gaskets 6 inch 300#
This is missing the gasket type, standard, facing type, material of construction (winding, filler, ring materials), and certification requirements. The supplier cannot determine whether you need a spiral wound, ring joint, soft sheet, or any other gasket type.
Common Pitfalls
| Pitfall | Why It Matters |
|---|---|
| Wrong color code accepted at receiving | The outer ring color on a spiral wound gasket identifies the winding/filler combination. A yellow ring means SS 304/graphite; a green ring means SS 316L/graphite. Accepting the wrong color means the wrong alloy is installed. Always verify color against ASME B16.20 Table 3 |
| Missing inner ring on large or high-class SWG | ASME B16.20 requires an inner ring for NPS 24” and above and for all Class 900 and above. Without the inner ring, the winding can buckle inward under bolt load, causing gasket failure and potential blowout |
| Using a spiral wound gasket on an RTJ flange | RTJ flanges have a machined groove designed for a solid metal ring joint gasket. A spiral wound gasket will not seat in the groove and cannot seal. Always match the gasket type to the flange facing: RF = spiral wound or soft gasket; RTJ = ring joint gasket |
| Not specifying filler material | ”Spiral wound gasket, SS 316L” is incomplete; the filler could be graphite, PTFE, or ceramic, each with different temperature limits and chemical compatibility. Always state the filler material |
| Oval ring on an octagonal-only groove | Octagonal rings can only be used in octagonal grooves. Oval rings can seat in both oval and octagonal grooves, but with reduced sealing efficiency in octagonal grooves. Verify the groove profile on the flange before ordering |
| Ring joint gasket harder than the flange groove | The ring must deform into the groove to seal. If the ring material is harder than the flange groove, the groove will be damaged. Select ring material softer than the flange material |
| Full-face vs ring gasket mismatch | Flat face (FF) flanges (common in cast iron per ASME B16.1) require full-face gaskets with bolt holes. Using a ring-type gasket on an FF flange concentrates bolt load on the raised area, risking flange cracking |
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