Ring type joints (RTJs) were initially developed for use in the petroleum industry, where high pressure/temperature applications necessitate a high integrity seal. They are mainly used in the oil field on drilling and completion equipment. Ring type joints are also commonly used on valves and pipework assemblies, along with some high integrity pressure vessel joints.
The material hardness of the RTJs must be less than the hardness of the flanges, to ensure that the RTJ is deformed and not the flanges when assembled.
How They Work
Under axial compressive load, RTJs plastically deform and flow into the irregularities of the flange groove. Since the load bearing area of the RTJ 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 allow very high internal pressures to be sealed. Since ring type joints are solid metal, their recovery characteristics are poor.
Standard Style R Ring Type Joints are manufactured in accordance with both API 6A and ASME B16.20 size/ratings. Available in both oval and octagonal configurations, both types are interchangeable on the modern octagonal type grooved flanges.
RX is an adaptation of the standard Style R and is designed to fit the same groove design as a Style R, making the gasket interchangeable. Consideration should be given to the difference in finished make-up distance. The modified design uses an energizing on assembly effect, which improves the efficiency of the seal. Designs are also available for Subsea applications.
The Style BX Ring Type Joints, manufactured in accordance with API 6A, are designed for use on pressurized systems up to 20,000 psi. When correctly fitted, the style BX gasket allows virtual face to face contact of the flange faces which means that the gasket is fully trapped on both the inner and outer diameters. All BX gaskets incorporate a pressure balance hole to ensure equalization of pressure which may be trapped in the grooves. Designs are also available for Subsea applications.