Raised Face vs Flat Face vs Ring Type Joint: Valve Flange Selection Guide | ASME B16.5

The Three Standard Flange Face Types

ASME B16.5 defines three standard flange facing types for pipe flanges and valve flanges: Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ). Each uses a different gasket and sealing approach. Selecting the correct face type is critical — using an RF flange against an FF flange (which is standard on cast iron fittings) can crack the cast iron flange under bolt tightening. Understanding when to specify each type prevents joint leaks and equipment damage.

Raised Face (RF) — The Standard for Industrial Service

Raised Face is the standard face type for Class 150–2500 carbon steel and alloy steel valves and pipe flanges per ASME B16.5. The raised face projects 1.6 mm above the flange face for Class 150–300, or 6.4 mm for Class 400–2500. The gasket contacts only the raised face area — concentrating the bolt load on the gasket seating surface for a reliable seal. RF is used with spiral wound gaskets (SWG) with outer centering ring and inner ring for Class 150–300, and SWG with inner ring or solid metal ring for Class 600 and above. Full-face gaskets are not used on RF flanges. ASME B16.5 requires RF face for all Class 150–2500 carbon and alloy steel flanges unless the purchaser specifies otherwise.

Flat Face (FF) — For Cast Iron and Soft Material Equipment

Flat Face means the entire flange face is machined flat, flush with the bolt circle — the gasket contacts the full face area including the bolt holes. FF is required when connecting to cast iron or ductile iron valves, pumps, compressors, and heat exchanger channels per ASME B16.5 Note regarding mating flanges: if a raised face steel flange is bolted to a flat face cast iron flange, the cast iron flange acts as a cantilever beam with the raised face serving as a fulcrum. The bolt tightening moment then bends the cast iron flange, which can crack or fracture. The correct solution is always to use FF flanges on both sides when one component is cast iron — with a full-face soft gasket (EPDM for water service, NBR for oil service, neoprene for chemical service). AWWA butterfly valves, standard pump casings, many heat exchanger channel heads, and low-pressure air compressor flanges are typically cast iron and require FF counterpart flanges.

Ring Type Joint (RTJ) — For Severe Service

Ring Type Joint (RTJ) uses a solid metallic ring gasket seated in a precisely machined groove in the flange face. The ring is available in three profiles: oval cross-section (R-type), octagonal cross-section (preferred — better seating efficiency and higher bolt load transmission), and pressure-energised profiles (RX and BX types used in API 6A wellhead connections). RTJ provides a true metal-to-metal seal and is the appropriate choice for: Class 600 and above high-pressure gas service where SWG gaskets may be marginal at sustained operating pressure; offshore wellheads and Christmas trees (API 6A RTJ is standard); hydrogen service where the small H2 molecule can permeate standard elastomeric and metallic-wound gaskets over time; subsea bolted connections where gasket replacement is impractical; NACE MR0175 sour service where elastomeric gasket materials require specific qualification. RTJ ring materials include soft iron (low hardness, general service), low-alloy steel F5/F11 (for alloy steel piping), and SS 316/316L (for stainless and duplex piping systems).

Flange Face Type vs Pressure Class — Selection Guide

Gasket Selection by Flange Face Type

• RF Class 150–300: Spiral wound gasket (SWG) with SS 304 or SS 316 outer centering ring and flexible graphite filler — per ASME B16.20.
• RF Class 600–2500: SWG with inner ring for added radial support, or solid metallic ring joint gasket where RTJ groove is machined.
• FF with cast iron: Full-face soft gasket — EPDM (water, steam below 180°C), NBR (oil, fuel), neoprene (chemicals) — 3.0–4.8 mm thickness, full-face to distribute bolt load.
• RTJ Class 600–2500: Solid metal ring — oval or octagonal cross-section; octagonal preferred for higher seating efficiency; SS 316 for stainless piping, low-alloy for carbon/alloy steel.
• Jacketed gasket: Used in heat exchangers and high-pressure steam heat transfer service where SWG seating is difficult due to rough or uneven flange surfaces.

Specifying Flange Face Type on Valve Orders

When ordering flanged valves, always specify the face type explicitly in the purchase order or material requisition (MR). Example: 'API 6D Trunnion Ball Valve, Class 600, 8 inch, RF (Raised Face) flanges per ASME B16.5' — or substitute 'RTJ' if the process piping specification requires ring type joint. Do not assume RF is the default — some manufacturers supply the same valve model in both RF and RTJ with different body configurations, and receiving the wrong face type creates costly rework at the fabrication shop or job site. Also specify the raised face finish: 125–250 AARH (Ra 3.2–6.3 µm) is standard for spiral wound gaskets; 63–125 AARH (Ra 1.6–3.2 µm) for ring joint and metal jacketed gaskets.