ASME flanged joints: RF, RTJ and FF facing types compared

In high-pressure piping, the integrity of the complete system depends on the flanged joints. Even when the pipes and flanges are correctly selected, leakage can still occur if the facing type is unsuitable for the service.

SalesSolution is a Russia-based Engineering & Supply Company manufacturing and supplying flanges, gaskets, studs, nuts, and other ASME pipeline components for oil & gas, petrochemical, chemical, and energy projects. Flange selection considers facing type, operating pressure, temperature, fluid service, mating-component materials, and documentation requirements.

ASME B16.5 and ASME B16.47 define the main Flange-facing types:

•   RF (Raised Face): a raised gasket seating surface

•   RTJ (Ring Type Joint): a metallic ring-joint sealing arrangement

•   FF (Flat Face): a full flat contact surface

Each type is intended for different pressure levels, fluids and operating conditions.

SalesSolution is a Russia-based Engineering & Supply Company manufacturing and supplying flanges, gaskets, studs, nuts and other ASME pipeline components for oil & gas, petrochemical, chemical and energy projects. Flange selection considers not only the facing type, but also operating pressure, temperature, fluid service, mating-component materials and documentation requirements. This integrated approach supports joint tightness and stable piping operation under the specified service conditions.

The function of the flange facing

The facing is the contact zone between two flanges. A gasket is installed in this zone, or a metallic ring seal is seated in machined grooves. Tightness is generated by stud preload, gasket or ring deformation and the resulting contact pressure.

In high-pressure piping, the facing area is exposed to:

•   axial loading

•   thermal deformation

•   vibration

•   pressure surges

•   cyclic stress

•   direct exposure to the process fluid

The selection of RF, RTJ or FF affects not only leak tightness, but also installation, maintainability, joint cost and machining requirements.

RF (Raised Face) Flanges

RF is the most common facing type for industrial flanges. The design has a raised annular seating area around the bore. A gasket is placed on this surface and compressed when the studs are tightened.

The load is concentrated over a limited gasket area. This raises the seating pressure and supports reliable sealing at medium and high pressure.

Advantages of RF

•   broad industrial applicability

•   compatibility with many gasket types

•   reliable tightness when the joint is tightened correctly

•   wide range of pressure classes

•   conventional installation procedures

•   broad availability of flanges and gaskets

Limitations of RF

•   sensitive to gasket quality

•   leakage risk if tightening is uneven or insufficient

•   less suitable for the most demanding very-high-pressure services

•   performance depends on the condition of the seating surface

RF is widely used in oil and gas piping, power plants, process lines and conventional industrial systems.

RTJ (Ring Type Joint): Metallic ring sealing

An RTJ Flange uses a metallic ring gasket seated in machined grooves rather than a soft sheet gasket. The ring normally has an oval or octagonal cross-section.

The ring is installed in accurately machined grooves. When the studs are tightened, the ring deforms locally and creates high-pressure metallic sealing contact with the groove surfaces.

Sealing principle

RTJ performance depends on controlled deformation of the metallic ring, high contact pressure, precise groove geometry and sufficient joint stiffness.

This arrangement is selected where a soft gasket cannot provide the required tightness under high pressure, temperature cycling or aggressive service.

Advantages of RTJ

•   the highest leak-tightness capability among standard facing arrangements

•   suitability for very high pressure

•   applicability in aggressive service

•   stable performance under cyclic loading

Limitations of RTJ

•   higher cost

•   more demanding machining

•   strict installation requirements

•   field repair is difficult without controlled tolerances

•   the ring gasket normally requires replacement after the joint is opened

RTJ is used in high-pressure oil and gas systems, offshore platforms, critical process lines and service containing H₂S or CO₂.

SalesSolution manufactures and supplies ASME B16.5 and ASME B16.47 Flanges in RF and RTJ configurations, together with ASTM A193 / A194 Fasteners and ASME B16.20 gaskets. For aggressive media, available Flange materials include ASTM A182 F316L, Duplex S31803, Super Duplex S32750 and nickel alloys.

FF (Flat Face) Flanges

An FF Flange has a fully flat face without a raised seating area.

The gasket covers the full flange face. The tightening load is distributed over a larger area, resulting in lower contact pressure than with RF or RTJ.

Advantages of FF

•   simple geometry

•   relatively low cost

•   straightforward installation

•   limited machining requirements

•   suitability for lower-pressure systems

Limitations of FF

•   restricted pressure capability

•   limited suitability for highly loaded systems

•   leakage risk under vibration

•   sensitivity to misalignment

•   narrow application range in high-pressure ASME systems

FF is used in water systems, lower-pressure services, pump stations and auxiliary lines.

Comparison of RF, RTJ and FF

How is flanged-joint tightness created?

Leak tightness is produced by the balance of three factors: stud preload, deformation of the sealing element and flange stiffness.

During operation, internal pressure tends to separate the flanges. The gasket or RTJ ring maintains sealing contact, while the Studs retain the initial preload.

If one part of this balance is lost, leakage can occur. The facing type must therefore be selected together with the pressure class, materials, gasket, fluid service and temperature.

Application in high-pressure piping

RF is the standard facing type in many industrial systems. It is commonly used across Class 150-600, although the final selection depends on the fluid, temperature, material and design pressure.

RTJ is selected where leak-tightness requirements are more demanding. It is commonly specified for Class 900-2500, high-pressure oil and gas service, and critical areas containing H₂S or CO₂ or operating offshore.

FF has a more limited role and is used mainly at low pressure and in non-critical service.

Common facing-selection errors

Mistake 1: using RF instead of RTJ for a service that requires a ring-joint seal. This increases the risk of gasket failure and leakage.

Mistake 2: installing an RTJ ring in inaccurately machined grooves. The ring cannot establish the required sealing contact.

Mistake 3: using FF in a vibration-prone system. The joint may gradually lose preload.

Mistake 4: using a gasket that does not match the facing. The wrong gasket can produce local leakage or damage.

Mistake 5: selecting the facing without considering the material. In aggressive service, the Flange, gasket and Fastener materials are as important as the choice between RF and RTJ.

Practical selection logic

A practical engineering sequence is:

•   conventional industrial systems: RF

•   high pressure and critical service: RTJ

•   low pressure and auxiliary lines: FF

•   aggressive media: RF or RTJ with suitable flange and gasket materials

•   offshore service and fluids containing H₂S / CO₂: RTJ or a project-specific engineered solution

The flange-facing type directly affects piping-system tightness

RF provides versatility. RTJ provides the highest sealing capability for very high pressure. FF provides simplicity and cost efficiency in low-pressure service.

In high-pressure systems, the choice between RF, RTJ and FF affects operating safety, joint tightness, piping life and total life-cycle cost.

Flanged joints for these applications are selected against the relevant standards, material grades, pressure class and fluid conditions. Correct selection reduces leakage risk and supports stable operation under the design conditions.

SalesSolution supplies coordinated packages of flanges, gaskets, fasteners and associated equipment to ASME standards, with engineering review, quality control and full documentation. Prior to 2022, SalesSolution worked with EPC contractors including Saipem, Toyo Engineering, Maire Tecnimont and The Linde Group.