Leak Tests at Real Bolted Flange Joints - Verification of Gasket Characteristics determined with Standardized Test Procedures

摘要

A prerequisite for the strength and tightness proof of bolted flange joints is the knowledge of gasket behaviour represented by several gasket factors. For floating type flanges joints, different calculation methods are used (e.g. ASME code in USA, the new European code EN 1591, or the KTA code 3211.2). Specific sets of gasket factors are defined which can be related to each other. For the choice of a gasket for given boundary conditions (construction, loading, temperature, medium,..) as well as for the calculation of bolted flanged joints (strength and tightness proof) gasket characteristics are required which reflect the deformation behaviour and sealing capability of the gasket. These gasket characteristics have to be determined with standardized test procedures in order to obtain comparable, reproducible and transferable results. For technical and economical reasons, the testing conditions of the standardized test procedures have to be idealised and simplified. But it is obvious that these testing conditions are not fully capable to consider the real conditions at bolted flange joints e.g. bending of flange blades, finite bolt distance, scatter of bolt load, or surface quality of flange face which might influence the actual leak rate significantly. Especially for existing flange joints at running power plants, there an exchange of flanges should be avoided, the fully knowledge about the actual leak behaviour during service is required to maximize tightness and to minimize material stress.