Metallic seals, such as lens gaskets and RTJ gaskets, are purely metallic profile gaskets manufactured by turning. They are designed for use at high pressures and temperatures. In the current version of EN 13555 (as of 2021), it is not possible to determine characteristic values for RTJ gaskets, for example, or to calculate joints in accordance with EN 1591-1. This is mainly due to the special geometry of the gasket and flanges compared to flat gaskets, the materials used and the area of application.
Unlike flat gaskets, RTJ gaskets (with oval profile) initially result in line contact between the flange and gasket during assembly due to the geometry of the components. The following figure shows a typical case for the installation situation of a gasket with an oval profile.
Symbolic representation of the installation situation of an RTJ gasket with oval profile
As the preload force increases, the contact area between the gasket and the flange increases. For this reason, a line force rather than a surface pressure should be assumed for this type of joint. RTJ gaskets also have profiles (e.g. octagonal) in which the gasket and flange have surface contact points. What all gaskets have in common is that the resulting leakage depends on how well the contact surfaces between gasket and flange match. The connection with metallic seals has special requirements in terms of the quality of the two surfaces and is also particularly dependent on the material pairing. The current version of EN 13555 does not yet specify any materials for testing these gasket types, and only the surface pressure is specified as a variable; however, in the case of gaskets with line contact, it is better to work with a line force.
Information for manufacturers of RTJ gaskets and users: Under certain conditions, it is possible to determine characteristic values for metallic seals and also provide them for calculation purposes. The data can be made available by the manufacturer via the gasketcloud.com platform for calculation purposes via the API interface. Calculators can import the data released there and use it in calculations with special attention. For more information go to gasketcloud.com.