Expired
Ring joint gaskets are heavy duty metallic ring type joint gaskets and largely used in onshore and offshore upstream and downstream petroleum and petrochemical applications where high pressures and temperatures are encountered. Ring joint gaskets are manufactured according to ASME B16.20 and API 6A standards.
There are three types of Ring Type Joint gasket designs, the R Type, RX Type and BX Type. The sealing surfaces on the ring joint grooves must have a smooth surface finish and should be free from ridges, tools or chatter marks. The hardness of the ring shall always be 15 to 20 HB lower than the hardness of the flange groove to prevent flange deformation and to allow plastic flow of the gasket into the flange faces.
With the right selection of material, ring joint type gaskets can withstand high pressures, temperatures and aggressive fluid service. A disadvantage of using RTJ flanges is that dirt or moisture can accumulate in the grooves when the flange is open. It is important that the grooves and ring gaskets are properly aligned in order to create a proper seal throughout the operating cycle. Gasket and flange surface finishes, dimensional accuracy and gasket hardness must be carefully controlled in order to obtain and maintain an effective seal. The minimum hardness requirements for gaskets are provided in Table 27 of API 6A 2020 edition.
R Type gaskets are are suitable for use with the flanges made to ANSI B16.5, ASME B16.47 series A and API 6A Standards. The R Type gaskets are designed for flanges with standard type ring grooves. They are most commonly used and are available in oval and octagonal section and are used to seal pressures up to 5000 psi in accordance with API 6A. The octagonal section has better sealability than the oval section and hence is the preferred gasket. Both the oval and octagonal section gaskets fit into the octagonal type grooved flanges. However, the octagonal ring type joint gasket cannot be used in the old type round bottom groove.
They are available in ring numbers from R11 to R105. The sealing surfaces on the ring joint grooves must have a smooth surface finish to 63 micro inches and should be free from ridges, tools or chatter marks.
RX Type gaskets are pressure activated ring joints designed to use the line service pressure to increase sealability. They are used for pressures up to 5000 psi (34.37 MPa) in accordance with API 6A for use with API 6B flanges. RX ring gaskets are similar in shape to the standard R type octagonal ring gasket but they have a non-symmetrical octagonal cross-section. Both R and RX octagonal gaskets use the same groove design and are interchangeable. Care should be taken when interchanging these types as RX gaskets are taller and will add length to the flanged joint assembly. The cross-section of RX type gaskets is designed to take advantage of the contained fluid pressure to provide tight sealing. The outside sealing surface of the ring joint gasket makes the initial contact with the flange. As the internal pressure increases the contact pressure between the ring joint and flange also increases thereby improving the gaskets sealing characteristics. This design feature allows the RX joints to be have more resistance to vibrations, pressure surges and shock loadings that are frequently encountered in the oil and gas industry.
They are available in ring numbers from RX 20 to RX215. The sealing surfaces on the ring joint grooves must have a smooth surface finish to 63 micro inches and should be free from ridges, tools or chatter marks.
BX Type gaskets are suitable only for use with API type 6BX flanges and are designed to seal pressures up to 20000 psi. They are available from pressure rating of 5000 psi to 20000 psi. The gasket differs from the R-type gasket in that it is square in cross-section with bevelled corners. These gaskets can be used only with API 6BX flanges and are not interchangeable with RX type gaskets. All BX gaskets have a pressure balance hole to ensure equalization of pressure which may get trapped in the grooves. The pitch diameter of the ring joint gasket is marginally larger than that of the flange groove. Thus when the ring joint is seated, it stays pre-compressed by the outside diameter creating high seating stress. When correctly fitted, the BX type gasket allows virtual face to face contact of the flange faces which means that the gasket in fully trapped on both the inner and outer diameters.
They are available in ring numbers from BX150 to BX303. The sealing surfaces on the ring joint grooves must have a smooth surface finish to 32 micro inches and should be free from ridges, tools or chatter marks.
API 6A Flange Sizes and Ratings
Table below provides a summary of API Type 6B and Type 6BX flange sizes for various ratings.
API 6A Gasket Ring Numbers for Type 6B and 6BX Flange Sizes
Table below provides a summary of Gasket Ring Numbers for API Type 6B and Type 6BX flange sizes for various ratings.
It is noted that for API Type 6BX flanges for ratings 2000, 3000 and 5000 are available only in larger sizes. The 6BX type flanges are not available for smaller sizes in these ratings.
ASME B16.5 Flange - Gasket Ring Numbers
Table below provides a summary of Gasket Ring Numbers for ASME B16.5 flange sizes for various ratings.
ASME B16.47 Series A Flange - Gasket Ring Numbers
Table below provides a summary of Gasket Ring Numbers for ASME B16.47 Series A flange sizes for various ratings.