Flanged Valve Connections: Standards and Face Finishing

ted wang
Jun 5
2 min read

Flanged end connections are the most common method for connecting valves to piping in process plants. Proper specification of flange rating, facing type, and gasket selection is critical for achieving leak-free connections.

Flange Standards

ASME B16.5: flanges from NPS 1/2 to 24, Class 150 through 2500
ASME B16.47: large bore flanges NPS 26 to 60 (Series A and B)
EN 1092-1: European flange standard with PN designations (PN 6 to PN 400)
API 6A: flanges for wellhead and Christmas tree equipment
MSS SP-44: steel pipeline flanges

Flange Face Types

The flange face type determines the gasket type and joint design. Proper matching of valve flange face to pipe flange face is critical.

Raised Face (RF): most common; gasket contacts raised face surface within bolt circle
Ring Type Joint (RTJ): octagonal or oval metallic ring seated in grooves; used for Class 600 and above
Flat Face (FF): used with cast iron and non-metallic flanges to prevent flange bending
Tongue and Groove (T&G): interlocking faces confine gasket; used in heat exchangers and special applications
Male and Female (M&F): similar to T&G but asymmetric

Surface Finish Requirements

ASME B16.20 and B16.5 specify surface finish requirements for flange faces. Raised face surfaces are typically finished to 125-250 Ra (AARH) for spiral wound gaskets and 63 Ra or better for ring joints. Phonographic (concentric serrated) finish is standard for raised faces used with spiral wound gaskets.

Gasket Selection

Spiral wound gaskets: standard for raised face flanges above Class 300 or where reliable sealing is critical
Kammprofile gaskets: grooved metal core with soft sealing layer; high reliability and reusability
Ring joint gaskets: metallic ring for RTJ flanges; soft iron, 304SS, 316SS, Monel
Sheet gaskets: used for low-pressure, non-critical services

Bolting Requirements

Flange bolting must be properly selected and torqued to achieve adequate gasket compression without exceeding flange or bolt design limits. ASME PCC-1 provides guidelines for pressure boundary bolted joint assembly.