Page 32 - Design Criteria.qxd

33 ® Welcome to the Next Generation of Sealing Technology
Ring Type Joints
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 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 CLA microinches Ra maximum (0.8 micrometer Ra)
Reuse
Ring type joints are designed to have a limited amount of positive interference, which ensures that the ring type joint seats cor-
rectly 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:
Maximum Hardness
Material Werkstoff Identification
Number Brinell* Rockwell B†
Soft Iron 90 56 D
Low Carbon Steel 120 68 S
4 - 6% Chrome 1/2% Moly. 130 72 F5
Type 304 Stainless Steel 1.4301 160 83 S304
Type 316 Stainless Steel 1.4401 160 83 S316
Type 347 Stainless Steel 1.4550 160 83 S347
Type 410 Stainless Steel 1.4006 170 86 S410
* Measured with 3000Kg load except soft iron which is measured with 500Kg load
† Measured with 100 Kg load and 1/16” diameter ball.
Some materials can be supplied with NACE certification on request.
Protective Coating
In accordance with API Specifications, soft iron, low carbon steel, and other ferrous materials ring type joints are protected from
corrosion with electroplated zinc or cadmium to a maximum thickness of 0.0005”. Alternative material coatings can be supplied
on request.