Ring-Type Joint (RTJ)

engineers November 20, 2019

The Ring Type Joint flanges are typically used in high pressure (Class 600 and higher rating) and/or high temperature services above 800°F (427°C). They have grooves cut into their faces which steel ring gaskets. The flanges seal when tightened bolts compress the gasket between the flanges into the grooves, deforming (or Coining) the gasket to make intimate contact inside the grooves, creating a metal to metal seal.

An RTJ flange may have a raised face with a ring groove machined into it. This raised face does not serve as any part of the sealing means. For RTJ flanges that seal with ring gaskets, the raised faces of the connected and tightened flanges may contact each other. In this case the compressed gasket will not bear additional load beyond the bolt tension, vibration and movement cannot further crush the gasket and lessen the connecting tension.

Ring Type Joint gaskets

Ring Type Joint gaskets are metallic sealing rings, suitable for high-pressure and high-temperature applications. They are always applied to special, accompanying flanges which ensure good, reliable sealing with the correct choice of profiles and material.

Ring Type Joint gaskets are designed to seal by "initial line contact" or wedging action between the mating flange and the gasket. By applying pressure on the seal interface through bolt force, the "softer" metal of the gasket flows into the microfine structure of the harder flange maused with ASME B16.5 flanges, class 150 to 2500. Style 'R' ring type joints are manufactured in both oval and octagonal configurations.

The OCTAGONAL ring has a higher sealing efficiency than the oval and would be the preferred gasket. However, only the oval cross section can be used in the old type round bottom groove. The newer flat bottom groove design will accept either the oval or the octagonal cross section.

Style R ring type joints are designed to seal pressure up to 6,250 psi in accordance with ASME B16.5 pressure ratings and up to 5,000 psi.

The RX type is suitable for pressures up to 700 bar. This RTJ is capable of sealing itself. The outer sealing surfaces make the first contact with the flanges. A higher system pressure causes a higher surface pressure. Type RX is interchangeable with the standard R-models.

The BX type is suitable for very high pressures up to 1500 bar. This ring joint is not interchangeable with other types, and is only suited for API type BX flanges and grooves.

The sealing surfaces on the ring joint grooves must be smoothly finished to 63 Microinches and be free of objectionable ridges, tool or chatter marks. They seal by an initial line contact or a wedging action as the compressive forces are applied. The hardness of the ring should always be less than the hardness of the flanges.