What Is ASME B16.20?

ASME B16.20 is the American standard that covers metallic gaskets for pipe flanges. It defines the dimensions, tolerances, materials, and marking requirements for spiral wound gaskets (SWG), ring type joint (RTJ) gaskets, and Kammprofile gaskets used with ASME B16.5 and ASME B16.47 flanges.

Attribute	Detail
Full title	Metallic Gaskets for Pipe Flanges; Ring-Joint, Spiral-Wound, and Jacketed
Scope	Metallic and semi-metallic gaskets for flanges per ASME B16.5, B16.47, and API 6A
Gasket types covered	Ring joint (R, RX, BX), spiral wound (with/without rings), Kammprofile, corrugated metal, metal-jacketed
Flange size range	NPS 1/2 through NPS 24 (B16.5) and NPS 26 through NPS 60 (B16.47)
Pressure classes	150, 300, 600, 900, 1500, 2500
Referenced by	ASME B31.3, B31.1, API 6A, project piping specifications
Companion standard	ASME B16.21 (non-metallic gaskets)

What ASME B16.20 Covers

The standard provides:

For Spiral Wound Gaskets:

• Inner and outer diameter dimensions by NPS and pressure class
• Winding metal and filler material options
• Outer ring (centering ring) dimensions and color-coding requirements
• Inner ring dimensions and when required
• Gasket type designations (CG, CGI)

For Ring Joint Gaskets:

• R-number designation system (ring number per size/class combination)
• Oval and octagonal cross-section dimensions
• RX and BX style dimensions
• Material hardness requirements
• Surface finish requirements (63 micro-inches Ra)

For Kammprofile (Camprofile) Gaskets:

• Serrated metal core dimensions
• Soft facing material specifications
• Dimensional tolerances

Gasket Marking

ASME B16.20 requires permanent marking on the gasket or its packaging. The marking must include:

Marking Element	Example
Manufacturer’s name or trademark	”ABC Gaskets”
NPS and pressure class	NPS 4 CL600
Gasket type	SWG-CGI / R-35 Oct
Winding/ring material	316
Filler material	Graphite
Ring number (RTJ only)	R-35

This marking allows field verification during pipe inspection and ensures the correct gasket is installed for each flanged joint.

How ASME B16.20 Relates to Other Standards

Standard	Relationship
ASME B16.5	Defines the flanges that B16.20 gaskets fit (NPS 1/2-24)
ASME B16.47	Defines large flanges (NPS 26-60) for B16.20 gaskets
ASME B16.21	Companion standard for non-metallic (soft) gaskets
ASME B31.3	Process piping code that references B16.20 for gasket selection
API 6A	Wellhead equipment standard; uses BX rings per B16.20 dimensions
ASME PCC-1	Guidelines for pressure boundary bolted flange joint assembly

Pro Tip

When writing a purchase order for metallic gaskets, reference ASME B16.20 explicitly and state the gasket type (SWG-CG, SWG-CGI, or RTJ with ring number), winding/ring material, filler material, and the applicable flange specification. Omitting any of these details leads to incorrect deliveries.

Correct gasket selection and bolt-up per ASME PCC-1 guidelines require that stud bolts are torqued to the values in the ASME B16.5 bolt chart for the specified flange class.

Read the full guide to gasket selection