In December 2013, a new version of EN 1591-1 (1) was issued. Apart from several other modifications, the treatment of external loads was included in this calculation standard for circular bolted flanged joints. In the former standard, only axial forces and bending moments resulting from the piping system were considered; in the new issue lateral forces and shear moments can also be treated.
There are two possibilities to counterbalance the lateral forces and the shear moments: firstly by metallic contact of the flanges and secondly by friction between the gasket and the flange surfaces. While the first option cannot occur in the type of flange connection (with a floating gasket between the flanges) covered by EN 1591-1, the lateral displacement of the flanges can only be prevented by friction between the gasket and flange surfaces. Therefore, the friction factor μG was introduced in the calculation procedure.
In an informative annex of EN 1591-1 (Annex E), some friction factors are published exemplarily. These factors are based on values published in the German nuclear codes KTA 3201.2 (2) and KTA 3211.2 (3). The origin of these values can’t be retraced anymore. For this reason, it is stated in Annex E that these values are probably very conservative, and that an experimental determination of the factors should be preferentially used. Incidentally, overly conservative friction factors lead to higher required bolt forces to counterbalance the external loads, which may result in an overstressing of the components of the bolted flanged joint.
Therefore, the European Sealing Association (ESA) decided to determine generic data for different types of gaskets which could be published in the next revision of EN 1591-1. In this paper the results of this project are presented.