ASME B16.20

Covers — materials, dimensions, tolerances, colour coding, and markings for metallic gaskets used with B16.5 and B16.47 flanges: spiral-wound (with inner/outer rings), ring-joint (RTJ oval/octagonal, and RX/BX pressure-energized), and jacketed types.

Facing pairing — match the gasket to the flange facing:

• Spiral-wound & jacketed → raised-face (RF) or flat-face (FF) flanges.
• RTJ → ring-joint grooved flanges only (R/RX in B16.5 grooves; BX for API 6BX high pressure).

Inner / outer rings — the outer (centering) ring locates the gasket on the bolt circle and limits compression; an inner ring is required for PTFE and flexible-graphite fillers, and for all spiral-wounds in Class 900 and above, to resist inward buckling.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Nonmetallic flat gaskets → ASME B16.21.
• Bolted-joint assembly and bolt load → ASME PCC-1.
• Flange dimensions/ratings → ASME B16.5 / B16.47; API high-pressure RTJ → API 6A.
• PN/European gaskets → EN 1514 / EN 12560.

B16.20 makes the gasket dimensionally correct; the joint's tightness still depends on the right filler and proper assembly.

B16.20 sets minimum requirements for metallic gaskets:

• Dimensions — spiral-wound, RTJ, and jacketed gasket sizes matched to flange size, class, and facing, with tolerances.
• Materials — winding/filler and ring-joint metal options for the service; RTJ ring hardness must be softer than the flange groove to avoid galling the seating surface.
• Ring types — RTJ styles R (oval/octagonal), RX and BX (pressure-energized); spiral-wound inner ring (anti-buckling) and outer centering ring.
• Colour Coding — a continuous colour band identifies the winding metal, and a colour stripe on the band identifies the filler — for at-a-glance verification.
• Marking — manufacturer, size, pressure class, winding/filler material, and standard reference stamped on the outer ring.

ASME B16.20 is the dimensional and identification standard for metallic gaskets used with ASME flanges — spiral-wound, ring-joint (RTJ), and jacketed. Its colour-coding scheme lets an inspector confirm the winding and filler at a glance, and its RTJ ring dimensions ensure the gasket seats correctly in the flange groove.

Spiral-wound colour code

A continuous colour band on the outer ring identifies the winding metal; colour stripes on the band identify the filler. Common codes:

Colour codes are safety-critical — always verify against the current ASME B16.20 tables; not every winding/filler is listed here.

RTJ ring types

• Style R — oval or octagonal; fits ASME B16.5 ring-joint grooves, Class 150–2500.
• Style RX — pressure-energized, interchangeable into R grooves; higher-pressure/API service.
• Style BX — pressure-energized for API 6BX flanges (very high pressure); ring and groove must share the same ring number.

Ring hardness must be softer than the flange groove to avoid galling. Because B16.20 is a dimensional/marking standard, actual sealing depends on the right filler and correct bolt load (ASME PCC-1). Nonmetallic gaskets fall under B16.21.

Engineering Note: Verify the spiral-wound inner/outer rings and the RTJ ring number against the flange, and check that the ring metal is softer than the groove — the right seal element in the wrong ring configuration (or too-hard an RTJ ring) is a frequent, avoidable leak or groove-damage.