Flange sealing surfaces determine where the gasket sits, how bolt load is transferred and how the joint is assembled. The face type must match the mating flange, gasket, applicable standard and service conditions. A flange face should never be selected from pressure alone.
Quick Answer
Raised face (RF) is widely used in process piping and concentrates gasket load on the raised sealing area. Flat face (FF) uses a gasket across the full flange face and is commonly specified where the mating equipment or flange standard requires it. Ring-type joint (RTJ) uses a precision metal ring and matching grooves for demanding pressure-temperature service. Tongue-and-groove and male-female faces are paired designs that locate and confine the gasket. Always order both mating faces, gasket style, pressure class, material and facing requirements as one compatible joint system.
Flange Face Types at a Glance
| Face type | How it seals | Common selection reason | RFQ caution |
|---|---|---|---|
| Raised Face (RF) | A gasket is compressed on the raised annular sealing area. | Common process-piping arrangement with many soft, semi-metallic and spiral-wound gasket systems. | Confirm pressure class, facing finish, gasket dimensions and the compatible mating face. |
| Flat Face (FF) | The gasket normally covers the full face inside the bolt circle. | Used where the equipment, flange material or governing standard calls for a full-face joint. | Do not mate RF and FF components unless the responsible engineer and applicable code specifically permit the arrangement. |
| Ring-Type Joint (RTJ) | A metal ring is loaded into matched precision grooves. | Selected for defined high-pressure or high-temperature services when required by the design specification. | State ring type, ring material, groove designation, flange class and dimensional standard. RF and RTJ are not interchangeable. |
| Tongue-and-Groove (T&G) | The gasket is located inside the groove and compressed by the mating tongue. | Provides controlled gasket location and helps limit lateral movement. | Tongue and groove are a matched pair. Confirm whether small or large geometry is required. |
| Male-and-Female (M&F) | The gasket sits in the female recess and is compressed by the mating male face. | Locates the gasket and provides more confinement than an open raised face. | Male and female faces must be ordered together with the correct gasket dimensions. |
Raised Face (RF)
A raised-face flange has a sealing area that projects above the bolting circle. Because the gasket contacts a smaller annular area than a full-face gasket, the available bolt load is concentrated on that sealing zone. RF flanges are common in ASME piping systems, but the correct gasket and facing finish still depend on the flange class, material, temperature, medium and joint design.
Buyers should not describe an RF flange only as “smooth” or “serrated.” The purchase order should identify the governing dimensional standard and any required surface-finish range or facing pattern. The gasket manufacturer’s limits must also be checked, especially for spiral-wound, graphite, PTFE and other gasket constructions.
Flat Face (FF)
A flat-face flange has no raised sealing land. A full-face gasket generally extends across the flange face and includes bolt holes. This arrangement can distribute gasket loading over a larger area and may be specified for particular equipment or flange materials.
The mating components must be reviewed as a system. Pulling an RF flange against a flat or comparatively flexible mating flange can introduce bending or uneven loading. The applicable piping or equipment code, flange standard and equipment manufacturer should determine whether the combination is acceptable.
Ring-Type Joint (RTJ)
RTJ flanges contain machined grooves that accept a metal ring gasket. Bolt load forces the ring against the groove surfaces to form the seal. The ring and grooves are engineered components; their geometry, material and hardness relationship must be compatible with the governing standard and service.
Do not place a soft flat gasket over an RTJ groove as a field substitute. For an RTJ quotation, identify the flange standard, nominal size, class, facing designation, ring number and ring material. Groove condition and dimensional inspection are especially important when flanges are reused.
Tongue-and-Groove and Male-Female Faces
These are paired face arrangements rather than two identical flanges. In a tongue-and-groove joint, the gasket is retained in the groove. In a male-female joint, the gasket is located in the female recess and compressed by the male face. Both designs help position and confine the gasket, but they require correct pairing and leave less room for field substitution.
Before ordering, confirm the exact geometry, small or large facing designation where applicable, gasket dimensions, assembly access and maintenance requirements. A correct face name without the matching mating detail is not a complete specification.
Why Surface Finish Matters
The face type locates the gasket; the facing finish influences how the gasket grips, flows and seals. Surface roughness, groove pattern, flatness and damage can all affect joint performance. A finish that is too smooth or too rough for the selected gasket may reduce sealing reliability.
- Specify the applicable flange standard and project revision.
- State the required face type and facing finish instead of using only a generic flange description.
- Protect sealing surfaces during machining, packing and transport.
- Inspect scratches, dents, corrosion and groove damage before assembly.
- Use gasket and bolting procedures approved for the complete joint.
How to Select a Flange Sealing Surface
- Start with the governing design basis. Confirm the piping code, equipment specification, flange standard and project requirements.
- Define the service. Provide design pressure and temperature, medium, corrosion conditions, cycling and leakage sensitivity.
- Match the joint components. The two flange faces, gasket, bolting and connected equipment must be compatible.
- Confirm dimensions and class. State NPS/DN, pressure class or PN rating, flange type, material grade and schedule or bore.
- Define inspection and documents. Add dimensional checks, facing inspection, material certificate and any project-specific NDE or PMI requirements.
Important:
A pressure class is not a universal working-pressure value, and a face type is not proof that a joint is suitable for a service. Material group, temperature, flange standard, gasket, bolting, piping code and equipment design must be evaluated together.
Common RFQ Mistakes
- Writing “standard flange” without identifying the standard, class and face.
- Ordering two identical faces when a tongue-groove or male-female pair is required.
- Using “RJ” or “ring face” without the RTJ groove and ring designation.
- Choosing a gasket before confirming facing finish and service conditions.
- Assuming flanges with the same nominal size and class will always mate across different standards.
- Ignoring protective packing for machined sealing faces during export shipment.
Flange RFQ Checklist
- Applicable standard and revision
- Flange type: weld neck, slip-on, blind, socket-weld, threaded or lap-joint
- NPS/DN, pressure class or PN rating, bore and pipe schedule
- Material grade and heat-treatment condition
- Face type: RF, FF, RTJ, tongue-and-groove or male-female
- Facing finish, RTJ ring number or paired-face geometry
- Gasket type, material and required standard
- Design pressure, design temperature and service medium
- Quantity, marking, MTC, inspection and packing requirements
- Delivery destination and required date
Need Stainless Steel Flanges With the Correct Facing?
Send the flange standard, size, class, material, face type, gasket requirement, quantity and destination. SAKY STEEL can review the RFQ and confirm available manufacturing and inspection options.
Post time: Sep-03-2023