How They Work:
Under axial compressive load, ring type joints plastically deform and flow into the irregularities of the flange groove. Since the load bearing area of the ring type joint is relatively small, very high surface stresses result between the sealing faces of the ring type joint and the groove. These stresses are further increased on the Style RX and BX rings which allows for very high internal pressures to be sealed.
Since ring type joints are solid metal, their recovery characteristics are poor. The seal is maintained by the action of axial load upon the gasket.
Surface Finish Requirements:
With all metal to metal type seals, it is imperative that the gasket and groove sealing faces are free from indentations, score marks,tool/chatter marks and other imperfections. The surface finish of the gasket and groove sealing faces is also critical and should not exceed the following:
Style R and RX 63 microinches Ra maximum (1.6 micrometer Ra)
Style BX 32 microinches Ra maximum (0.8 micrometer Ra)
Ring type joints are designed to have a limited amount of positive interference, which ensures that the ring type joint seats correctly into the groove on compression. Their reuse is not recommended for two reasons:
The initial seating of the gasket will be impaired.
When the gasket is plastically deformed, work hardening of the external metal surface occurs. This may result in
permanent damage to the groove.
Hardness of Materials:
On compression of the flange assembly, it is imperative that the ring type joint be significantly softer than the flange groove so that the gasket plastically deforms and not the groove. The use of harder ring type joints can result in flange groove damage. For this reason, ring type joints are supplied with the following maximum hardness values: