Upcoming Changes To ASME B16.20 Standard

The ASME B16.20 standard has been updated recently to accommodate some changes related to spiral wound gaskets. The new metricated edition of this standard makes the inner rings a default for graphite filled spiral wound gaskets. The purchaser can specify these gaskets without inner rings, however. Either way, the outer rings will be stamped ASME B16.20. This new revision has been balloted and approved at the Sub Committee and Main Committee levels. It has also been approved by ANSI. The new published document is expected to be out by the end of the first quarter of 2008.

Following is the approved new language: 

Inner Ring. Inward buckling of spiral wound gaskets has been identified as a potential problem. Inner rings shall be furnished with all spiral-wound gaskets having PTFE (polytetrafluoroethylene) filler material. Inner rings for flexible graphite filled spiral wound gaskets shall be furnished unless the purchaser specifies otherwise. For all filler materials, inner rings shall be furnished in spiral wound gaskets for:

a) NPS 24 and larger in Class 900

b) NPS 12 and larger in Class 1500

c) NPS 4 and larger in Class 2500

Inner rings are required for these gaskets due to high available bolt loads, which may result in outer ring damage. The inner ring thickness shall be from 2.97 to 3.33mm (0.117 to 0.131 in). Tables 12 through 14 (Tables I.12 through I.14 of Appendix I ) show inner ring inside diameters that may extend a maximum of 1.5mm ( 0.06 in. ) into the flange bore under the worst combination of flange bore, eccentric installation, and tolerance. Gaskets with inner rings should be used only with socket welding, lapped, welding neck, and integral flanges. Reference Table 15 for minimum pipe wall thickness for use with gaskets with inner rings. Reference Tables 16, 17 and 18 (Tables I.16 and I.17 of Appendix I) for maximum allowable bore for use with gaskets without inner rings."