Why 'ASME Gasket' Is Not a Complete Description

When buyers write 'ASME gasket' in an RFQ, they assume a single standard defines the product. It does not. ASME publishes separate standards for metallic and nonmetallic flat gaskets, and each has a different product scope.

ASME B16.20 covers metallic gaskets: ring-joint, spiral-wound, and metal jacketed, plus filler material. These gaskets are dimensionally suitable for use with flanges described in ASME B16.5, ASME B16.47, and API 6A. Spiral-wound and metal jacketed gaskets are covered for use with raised face and flat face flanges.
ASME B16.21 covers nonmetallic flat gaskets: types, sizes, materials, dimensions, tolerances, and markings. The standard states that these gaskets are dimensionally suitable for flanges described in the referenced flange standards.

The phrase 'ASME gasket' omits the two most important decisions: which gasket family you need and which flange facing it must match. A complete description must name the standard, the gasket type, material, dimensions, and the intended flange facing.

Flange Facing Basics Buyers Must Confirm

Flange facing determines how a gasket sits and seals. The facings referenced in the B16.20 scope are raised face, flat face, and ring-joint. The flange standard defines the facing geometry; the gasket standard defines the gasket geometry. Neither standard in the source scope supplies an interchange table between facing type and gasket type. The buyer must confirm the facing from the flange standard and the gasket design from the gasket standard, then verify that the manufacturer's product matches both.

Do not assume a nonmetallic flat gasket is correct for every raised face flange, or that a spiral-wound gasket can be substituted for a ring-joint gasket without rechecking the flange dimensions and service conditions.

Checklist: Matching Gasket Standard to Flange Type

Use this checklist before you send an inquiry to a flange or gasket supplier.

Identify the flange standard: ASME B16.5, B16.47, or API 6A for the flange you are mating. Confirm the edition and pressure class.
Identify the flange facing from the flange standard: raised face, flat face, ring joint, or another controlled profile.
Choose the gasket family:

- Metallic ring-joint, spiral-wound, or metal jacketed gasket: ASME B16.20.
- Nonmetallic flat gasket: ASME B16.21.

Cross-check the gasket type against the facing:

- Ring-joint flanges require ring-joint gaskets, not flat gaskets.
- Raised face flanges can use spiral-wound or metal jacketed gaskets under B16.20, but the exact facing dimensions and gasket construction must match the flange.
- Flat face flanges should be reviewed for gasket type compatibility with the flange's pressure class and service.

Confirm material and filler: B16.20 includes filler material for spiral-wound gaskets; B16.21 covers nonmetallic flat gasket materials. Material selection is a service decision, not just a dimensional one.
Verify dimensions, tolerances, and markings against the applicable standard. The supplier should state which edition they manufacture to.

Procurement Checks Before RFQ

Before you issue an RFQ, gather the information the supplier will need:

Flange standard and edition, nominal size, pressure class, facing, and bore details from the flange data sheet.
Gasket standard and edition: B16.20 or B16.21.
Gasket type and material or filler specification.
Service conditions that affect gasket selection: temperature, pressure, fluid, bolting, and any requirements such as fire-safe or low-emission service. The public scopes of the two standards do not provide service limits, so these must be defined by the project specification or the gasket manufacturer's published ratings.
Marking and traceability requirements, including any certificate format.

The more complete the RFQ, the fewer 'shall we assume' conversations you will have after purchase. If a supplier offers 'ASME gaskets' without naming the standard and facing, treat it as an incomplete response.

What to Put in Your RFQ

Include these line items in every gasket RFQ:

Nominal pipe size and flange standard (ASME B16.5, B16.47, API 6A) with edition
Flange facing and pressure class
Gasket standard: ASME B16.20 or ASME B16.21 (edition)
Gasket type: ring joint, spiral-wound, metal jacketed, or nonmetallic flat
Material, filler, and any coating or inner/outer ring requirement
Dimensions and tolerances per the standard, or a drawing for special profiles
Quantity and packaging requirements
Required documentation: material certificates, inspection reports, and marking confirmation

If you are sourcing complete flange and gasket packages, use the same details for the flange and gasket so the supplied components can be verified together. Our products page lists flange and fitting options, but the compatibility check still belongs to the project engineer and inspector.

Inspection and Documentation Points

When the shipment arrives, verify the gasket against the order and the standard:

Compare markings to the standard and the PO. Gasket markings should include the standard designation, size, and material identification as required.
Check dimensions and tolerances against the standard's tables. Use calibrated instruments.
Confirm the gasket design matches the flange facing. A ring-joint gasket cannot be installed on a raised face flange, and a flat nonmetallic gasket may not fit an RTJ groove.
Review material certificates against the specified material and filler.
Verify that the gasket standard edition matches the order. Do not accept a different edition without engineering review.
Inspect packaging and storage conditions. Gaskets must be protected from damage, moisture, and contamination.

For large or critical orders, consider third-party dimensional inspection. The cost is low compared with the risk of a field leak.

Common Risks and How to Avoid Them

Incomplete specification: Ordering 'ASME gasket' without standard and facing. Fix: name B16.20 or B16.21 and the facing.
Wrong family for the facing: Using a nonmetallic flat gasket where a metal ring-joint or spiral-wound gasket is required, or vice versa. Fix: cross-check before ordering.
Edition mismatch: The standard you reference may differ from the edition the supplier manufactures. Fix: write the edition into the RFQ and the PO.
Missing service rating: The public scopes of the standards do not list temperature or pressure limits. Fix: use manufacturer ratings and the project design code.
Assumed interchangeability: Assuming a gasket from a different standard or material will fit simply because the size matches. Fix: verify dimensions against the standard.

Final Word

Gasket compatibility is a two-side check: the flange standard describes the flange, and the gasket standard describes the gasket. Neither B16.20 nor B16.21 is a universal 'ASME gasket' reference. Confirm the flange facing, select the correct gasket family, and state both standards explicitly in your RFQ and inspection plan.

If you need to move from specification to sourcing, send your intended standard, facing, and service details through our inquiry page. The more data you provide, the more precisely we can respond to your request.

Sources

https://www.asme.org/codes-standards/find-codes-standards/b16-20-metallic-gaskets-pipe-flanges
https://www.asme.org/codes-standards/find-codes-standards/b16-21-nonmetallic-flat-gaskets-pipe-flanges