ASME B16.20: Metallic Gaskets for Pipe Flanges

ASME B16.20 Standard covers materials, dimensions, tolerances, and markings for metal ring-joint gaskets, spiral-wound metal gaskets, metal-jacketed gaskets, and grooved metal gaskets with covering layers. These gaskets are dimen-sionally suitable for use with flanges described in refer-ence flange standards ASME B16.5, ASME B16.47, API Specification 6A, and ISO 10423.

Table RJ-3.2-1 Maximum Hardness for Ring Gaskets

Ring Gasket Material Maximum Hardness
Brinell Rockwell "B" Scale
Sof Iron  [Note (1)]  90 56
Low-carbon steel 120 68
4-6 chorme 1/2 Mo 130 72
Type 410 170 86
Type 304 160 83
Type 316 160 83
Type 316 160 83

NOTE: (1) Maybelow-carbonsteel,nottoexceedmaximumhardness of 90 Brinell — 56 Rockwell “B.”

Table RJ-4-1 Ring Gasket Markings

Ring Gasket Material Identification Marking Example[Note (1)]
Sof Iron D  [Note (2)]  R51D
Low-carbon steel S R51S
4-6 chorme 1/2 Mo F5 [Note (3)]  R51F
Type 410 S 410 R51S410
Type 304 S 304 R51S304
Type 316 S 316 R51S316
Type 347 S 347 R51S347


(1) This number shall be preceded by the manufacturer’s name or identification trademark.

(2) May be low-carbon steel, notto exceed maximum hardness of 90. Brinell — 56 Rockwell “B.”

(3) F5 identification designates ASTM specification A182-72 chemical composition requirements only. 

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