ASME B16.20-2012 pdf download – Metallic Gaskets for Pipe Flanges Ring-Joint, Spiral-Wound,and Jacketed.
5.2 Dimensions and Tolerances
5.2.1 General. Dimensions and tolerances for grooved nwtal gaskets with covering layers and centering rings shall be in accordance with Fig. 3 and Tables 26 through 28 (Tables 1-15 through 1-17 of Mandatory Appendix I) and as specified in this section.
5.2.2 Construction. Grooved metal gaskets with covering layers shall be 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 (0.018-in.) to 0.56-mm (0.022-in.) thick. The thickness of the metal core of the gasket shall be 2.97 mm (0.117 in.) to 3.33 mm (0.131 in.). The thickness on any single gasket shall be uniform within a maximum tolerance range of 0.13 mm (0.005 in.).
5.2.3 Welding. Welding is permitted only in NPS 14 and larger gaskets. Welding shall be subject to the following:
(a) Full penetration welds shall be used.
(b) Where only two welds are used, the minimum weld spacing shall be 152 mm (6 in.). Where more than two welds are 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 grooves 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.
(e) When specified by the purchaser, weld inspection methods, such as ultrasonic or radiographic, along with acceptance criteria, shall be established.
5.2.4 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 be 1.6-mm (0.06-in.) nominal thickness 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.
5.4.2 Pressure Class. Gaskets suitable for more than one pressure class shall be marked with all applicable classes, as shown in Table 30.
5.4.3 Color Coding. Gaskets shall be marked with a color code that identifies the metal core and facing materials. A continuous color around the outer edge of the centering ring shall identify the core metal. The color identifying the facing material for NPS 3 and larger shall have a minimum of four stripes equally spaced on the outer edge of the centering ring. Smaller size gaskets shall have a minimum of two stripes 180 deg apart. The colors shall conform to those listed in Table 29. Special material not listed in Table 29 shall not be color coded. Users shall refer to the guide ring marking for material.