Probabilistic Procedure to Evaluate Integrity of Degraded Pipes

Abstract

The determination of critical crack sizes or permissible/allowable loading levels in pipes with degraded pipe sections (circumferential cracks) for the assurance of component integrity is usually based on deterministic approaches. Therefore along with numerical calculation methods (finite element (FE) analyses) limit load calculations, such as e.g. the “Plastic limit load concept” and the “Flow stress concept” as well as fracture mechanics approximation methods as e.g. the R-curve method or the “Ductile fracture handbook” and the R6-Method are currently used for practical application. Numerous experimental tests on both ferritic and austenitic pipes with different pipe dimensions were investigated at MPA Stuttgart. The geometries of the pipes were comparable to actual piping systems in Power Plants. Different crack geometries and dimensions were considered. A new post-calculation of the above mentioned tests was performed using probabilistic approaches to assure the component integrity of degraded piping systems. As a result the calculated probability of failure was compared to experimental behaviour during the pipe test. The influence of the performance of non-destructive tests on the probability of failure was also taken into account. Different reliability techniques were used for the verification of the probabilistic approaches.