RTJ Flange (Ring Type Joint): Definition, Applications, and Repair

RTJ Flange machining

What is an RTJ Flange (Ring Type Joint)?


The RTJ flange (Ring Type Joint) is designed for high-pressure and/or high-temperature pipeline applications. This makes them the required standard in API specification flanges.
Applications include oil field valves, pipework assemblies, and high integrity pressure vessel joints.

Like other flanges, they use a gasket under compression to create a secure joint. But an RTJ flange differs from the more common flat and raised face flange in several ways:

  • The gasket used is a steel ring – instead of the flat composite material type.
  • An RTJ flange has a groove machined into the flange surface to accept the gasket.
  • When the gasket deforms it creates a metal-to-metal seal.
  • Under compression, the softer metal of the gasket flows into the microfine structure of the harder flange material.
  • The raised faces of connected and tightened RTJ flanges may be in contact with each other. When this happens, the compressed gasket will not bear any extra load. The benefit is the integrity of the joint will be protected from over-tightening, vibration, and movement.

RTJ Flange Materials

  • Stainless Steel
  • Duplex & Super Duplex Steel
  • Carbon Steel
  • Low-Temperature Carbon Steel
  • Alloy Steel
  • Copper Alloy
  • Nickel Alloy

RTJ Flange Gasket Materials

Select the gasket to suit the service conditions. It is always recommended that the gasket material is softer than the mating flange.

RTJ gaskets are available in materials that include, Soft Iron, Low Carbon Steel, Stainless Steel, Titanium, Hastelloy, and Super Duplex.

Types of RTJ Gaskets

Types of RTJ Flange including R Oval, R Octagonal, RX, and BX.

Style R Gasket Rings

This is the original and basic type of RTJ gasket design for the high temperatures and pressures experienced in the oil and gas and petrochemical industries. In accordance with ASME B16.5 they are intended for pressure ratings up to 5,000 psi. R type gaskets are available with an oval or octagonal cross-section.

Style RX Gasket Rings

The Style RX is an adaptation of the standard Style R. The RX is designed to fit the same groove design as a standard Style R – making the joints interchangeable. RX rings use a pressure-energized effect that improves the efficiency of the seal as the internal pressure increases. Pressure passage holes are included in sizes RX 82 through to RX 91, which allows the pressure to be equalized.

Style BX

BX Ring Type Joints gaskets are designed for the highest pressurized systems from 5000 up to 20,000 psi. The design allows face to face contact of the flange faces – which means the gasket is fully trapped on both the inner and outer diameters. These also feature a pressure balance hole to relieve air pressure trapped within the grooves. They cannot be interchanged with the other two types.

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Machining RTJ Flange Grooves

The sealing face on a ring-type flange is not spiral serrated as used you see on a raised face flange. Instead, the sealing surfaces are smooth and mirror-like. These need to be finished to 63 microinches and should be free from ridges, scratches, or chatter marks.

When machining ring-type joint grooves onsite, the resulting dimensions need to be as described in the standard ASME B16.5.

This can be carried out on-site using a flange facing machine. Machines from Enerpac do not require any optional extras to complete RTJ machining. These are commonly used to machine RTJ flanges.

Flange facing machines for RTJ machining splits into two capabilities to create the 23° seal faces. Machines with auto-axial feed use an in-built axial gearbox, whereas others use a ‘kick-feed’ for the axial feed. (Both types are also capable of manual feed by the operator).

  • Auto-axial feed type – Ideal for RTJ machining. Examples with this feature include the MM1000i, MM1500i, MM2000i, MM600e models.
  • Striker kick feed type– where the axial feed is achieved by a striker or manually by tye operator. Examples include the MM300E, MM305i, and MM610i.

More Resources

References

http://www.pipingpipeline.com/asme-b16-5-flg-facing-finish.html

 https://flexitallic.com/wp-content/uploads/product-documents/us/Ring_Type_Joints_(RTJ).pdf