ASME B16.47 Flange Facing Finish

What’s the flange facing finish?

Pipe flanges manufactured in accordance with ASME B16.47, either Series A or Series B, welding neck or blind, may be furnished with 3 types of flange facings: raused face(RF), flat face(FF), or ring joint face(RTJ). Similar to ASME B16.5 flanges, the finish of the gasket contact faces shall be judged by visual comparison with Ra standrads in accordance with ASME B46.1 and not electronic amplification.

Different types of flange facing finish

For ASME B16.47 flanges with RTJ facing, the side wall surface finish of the gasket groove shall not exceed 1.6µm[63µinch] roughness. For flanges with RF or FF facings, either a serrated concentric or serrated spiral finish, having a resultant surface finish from 3.2 μm to 6.3 μm [125 μinch to 250μinch] average roughness shall be furnished. The cutting tool employed should have an approximate 1.5 mm [0.06inch] or larger radius, and there should be from 1.8 grooves / mm through 2.2 grooves / mm [45 grooves / inch through 55 grooves / inch].

Flange facing finish imperfections

Imperfections such as scratches in the facing finish of ASME B16.47 flanges shall be precisely controled to avoid radial leak paths. Adjacent imperfections shall be separated by a distance of least 4 times the maximum radial projection. A radial projection shall be measured by the difference between an outer radius and inner radius encompassing the imperfection where the radii are struck from the centerline of the bore. Imperfections less than half the depth of the serrations shall not be considered cause for rejection. Protrusions above the serrations are not permitted. The dimensioned limits of imperfections in flange facing finish are listed in the table below.