ASME B16.20-2017 pdf – Metallic Gaskets for Pipe Flanges.
The outer surface of each gasket shall carry the manuIacturer s name or identIfication trademark and gasket number prefixed by the letters R. RX. or BX. followed by the gasket material Identification. Materials shall be identified as shown In Table RI-4-1. The gasket shall also be marked with an ASME 816.20 designation. The marking shall be applied so as not to harmfully distort the gasket or affect the integrity of the seal.
Dimensions and tolerances for rlng-oInt gaskets shall be as shown in Tables RI-S-i through RJ-5-6.
Types R and RX gaskets shall have a surface finish not rougher than 16 llm (63 pin) roughncss Type RX gaskets shall have a surface finish not rougher than 0.8 im (32 Mm.) roughness. Surface finish shall pertain to the gasket-sealing surface.
Dimensional reference identification numbers arc assigned to ring-joint gaskets and shown in Tables RJ. S-i through RJ-S.6.
Grooved metal gaskets with covering layers having a centering ring are identified by flange size (NIS). pressure class, and the appropriate tlangc standard (ASME B 16,5 or ASME B 16.47).
GM-2.i GeneraL
Dimensions and tolerances for grooved metal gaskets with covering layers and centering rings shall be as spedfied in this Part and in accordance with Figure GM-2.i-1 and Tables GM-2.1-1 through GM-2.I-3.
GM-2.2 ConstructIon
Grooved metal gaskets with covering Layers shall he constructed as a concentrically grooved metal core (sealing element) with a centering ring. The grooved metal portion of the finished gasket shall be faced with a covering layer on both sealing surfaces that is 0.46 mm to 0.56mm (0.018 in. to 0.022 in.) thick. The thickness of the metal core of the gasket shall be 2.97mm to 3.33mm (0.117 in. to 0.131 in.). The thickness on any single gasket shall be uniform within a maximum tolerance range of 0.13 mm (0.005 In.).
GM-2.3 WeLding
Welding is permitted only in N PS 14 and larger gaskets. Welding shall be subject to the lollowing;
(a) Full penetration welds shall he used.
(b) Where only two welds are used, the minimum weld spacing shall be 152 mm (6 in.). Where more than two welds arc required, minimum weld spacing shall be 609 mm (24 in.). Weld spacing shall be measured along the Inside circumference of the metal core. When material availability precludes this weld spacing, then additional welding, as agreed by the purchaser and manufacturer, is permitted
(c) The groovcs shall be machined into the core after welding.
(d) In welded areas, the groove, peak profile, and base metal shall be uniform in spacing, thickness, and height with the adjacent metal core.
(c) When specified by the purchaser, weld inspection methods, such as ultrasonic or radiographic, along with acceptance criteria, shall be established.
GM-2.4 Centering Ring
A centering ring is required and used to help position the gasket within the flange bolt circle. Unless otherwise specified by the purchaser, the centering ring shall have a nominal thickness of 1.6 mm (006 in.) and shall be suitably attached to the grooved metal core using an integral (one-piece or welded) or nonintegral attachment method. The thickness of the centering ring shall not exceed the thickness of the core.
GM-3.1 Covering
Covering material shall be selected from Table GM-3.l-
GM-3.2 Core
Core material shall be selected from Table GM-3.1-1.
GM-3.3 Centering Ring
When carbon wd centering rings are selected, they shall be painted, metal plated, or otherwise coated to inhibit atmospheric corrosion.
GM-41 Generat
The centering ring shall be permanently marked. The lettering height shall be a minimum of 2.5 mm (0.1 in.), except where space requirements dictate use of a smaller size character. The following information shall be included:
(a) manufacturer’s name or trademark
(b) flange size (NPS).
(c) pressure class.
(d) metal core abbreviation (Table GM-3.1-1). except that the abbreviation may be omitted when Type 304 stainless steel is used.
(e) covering material abbreviation (Table GM-3.1- 1).