Flange Facing Types: RF, FF, RTJ, MF, TG — When to Specify Each
The flange facing type controls how the gasket seals the joint — get it wrong and the joint leaks even with correct bolting torque. The most common error is specifying Flat Face flanges with Raised Face equipment nozzles, or ordering RTJ flanges without matching RTJ groove dimensions. This article covers the five standard facing types, their applications, and the code requirements that govern each.
Raised Face (RF)
The standard facing for most industrial piping. The gasket contacts only the raised circular face — typically a 2 mm (ASME Class 150/300) or 7 mm (Class 400 and above) raised ring. RF flanges use spiral-wound gaskets (SWG) with outer ring for Classes 150–600, or SWG with inner and outer rings at higher pressures. ASME B16.5 RF surface finish: 125–250 µin Ra (stock finish) for spiral-wound gaskets; 63 µin Ra for ring gaskets. RF is suitable for most process services including steam, hydrocarbons, and general chemical. Avoid RF in caustic or HF acid service where even minor leakage is hazardous — use RTJ instead.
Flat Face (FF)
The gasket covers the full face, including the bolt holes. FF is used when mating to equipment with flat-face flanges — cast iron pumps and valves, glass-lined vessels, and PTFE-lined equipment. Critical rule: Never mate a Raised Face steel flange to a Flat Face cast iron flange. The contact stress from the raised face on the cast iron results in bending moments that can fracture the cast iron flange. FF steel flanges with full-face rubber gaskets are the correct pairing. ASME B31.3 requires FF gaskets when connecting to cast iron or other brittle materials.
Ring Type Joint (RTJ)
A metal ring (oval or octagonal cross-section) seats in a machined groove in both flanges. RTJ is the high-integrity facing for high-pressure and high-temperature service. ASME B16.5 Class 900 and above RTJ is common in wellhead, refinery, and offshore applications. The metal-to-metal contact provides a self-energising seal — higher pressure increases seating stress. RTJ flanges require RTJ-compatible valves and equipment with matching groove dimensions — always specify ring number (R-24, R-44, BX-153 etc.) on the PO. Ring hardness must be lower than the flange hardness to ensure the ring deforms into the groove.
Male-Female (MF) and Tongue-and-Groove (TG)
Both MF and TG require a matched pair — one male and one female (or tongue and groove). The gasket is captured, which prevents blow-out and constrains the gasket to a precise seating area. Used in chemical process where a full-face gasket could allow gasket creep and re-torquing is difficult. Not interchangeable with RF — MF pairs must be ordered as a set from the same manufacturer to ensure dimensional compatibility.
EN 1092 vs ASME B16.5 Facing Types
| EN 1092 Facing Code | Description | ASME B16.5 Equivalent |
|---|---|---|
| Type A | Smooth — full-face | Flat Face (FF) |
| Type B | Smooth — raised face | Raised Face (RF) |
| Type C | Tongue | Tongue (TG pair) |
| Type D | Groove | Groove (TG pair) |
| Type E | Male | Male (MF pair) |
| Type F | Female | Female (MF pair) |
| Type G | O-ring groove (male) | No direct equivalent |
EN 1092 Type B (raised face) is the most common for European process plants. The RF height in EN 1092 differs from ASME B16.5 — EN flanges have a 2 mm raised face height across all pressure ratings (PN 10–PN 400), while ASME flanges increase from 2 mm to 7 mm at Class 400. This dimensional difference must be considered when mixing EN and ASME flanges on a project.
Surface Finish Requirements
For spiral-wound gaskets on RF flanges: ASME B16.5 specifies 125–250 µin (3.2–6.3 µm) Ra — a phonographic (concentric serrated) finish produced by turning at specific feed rate. For ring joint gaskets (RTJ): 63 µin (1.6 µm) Ra or better on the groove. For PTFE/ePTFE sheet gaskets: smooth machine finish 63 µin or better. Always specify the gasket type on the flange PO — the facing and finish must be matched to the gasket design.