Winding our way to Metrication

Well the time has arrived after years of numerous and exhausting debates and discussions where the gasket industry will be joining the rest of the industry in the practice of metrication.  The recent edition of ASME B 16.20, Metallic Gaskets for Pipe Flanges lists metric units for all the gaskets covered in the standard, which include Ring-Joint, Spiral-Wound and Jacketed gaskets. Many of the other ASME B16 standards, if not all, have already made the conversion.

The new edition ASME B16.20-2007 covers not only dimensions converted to millimeters from inches, but uses µm to designate surface finishes in place of the customary µin. It now refers to MPa (Mega Pascal) instead of pounds/square inch (psi) when expressing unit stress.

The conversion from customary inch units to metric units consists of multiplying the inch units by 25.4 and rounding off to the nearest decimal, while tolerances are kept to the nearest two decimals.

Flange sizes and Pressure Classes remain designated as NPS and Class.

Tables listing dimensions of gaskets in U.S. Customary units can still be found in the back of the standard as Mandatory Appendix I. It’s however not clear at this juncture that Appendix I will remain in future editions.