Highlight of changes from prior edition: The 2003 edition of B16.5 includes metric units as the primary reference units while maintaining US Customary units in either parenthetical or separate forms. Several new materials have been added to the standard. All pressure-temperature ratings have been recalculated using data from the latest edition of the ASME Boiler and Pressure Vessel Code, Section II, Part D. In addition, straight hub welding flanges have been incorporated as a new set of flanges in Classes 150 through 2500. There are also numerous requirement clarifications and editorial revisions.

Scope B16.5-2003: This standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings. Included are:

Flanges with rating class designations 150, 300, 400, 600, 900, 1500 and 2500 in sizes NPS 1/2 through NPS 24 with requirements given in both metric and US Customary Units with diameter of bolts and flange bolt holes expressed in inch units; flanges fittings with rating class designation 150 and 300 in sizes NPS 1/2 through NPS 24 with requirements given in both metric and US Customary Units with diameter of bolts and flanges bolt holes expressed in inch units; flanged fittings with rating class designation 400, 600, 900, 1500, and 2500 in sizes NPS 1/2 through NPS 24 that are acknowledged in a nonmandatory Annex G in which only US Customary Units are provided.

This standard is limited to:
Flanges and flanged fittings made from cast or forged materials and Blind flanges and certain reducing flanges made from cast, forged, or plate materials. Also included in this standard are requirements and recommendations regarding flange bolting, flange gaskets and flange joints.