Modeling of Thermal Shock Effects on a Globe Valve Body-Bonnet Bolted Flange Joint

Advances in computational mechanics allow to improve safety and reliability of many components used in nuclear applications. Although valves are numerous and critical for safety considerations, many difficulties arise that highly complicate the use of numerical methods for qualification and testing. Thus, valves are mainly tested by experimental simulation in representative conditions, which is sufficient to prevent failures, but do not help to comprehensively analyze mechanisms of failure. This paper attends to demonstrate efforts made at EDF R&D to improve comprehension of valve parts loadings during operation. Thermal shock in a globe valve is represented and modeled using EDF R&D Finite Element Analysis (FEA) code (Code_Aster). Since the globe valve representation implies several parts, attention is first focused on Boundary Conditions (BC) and meshing refinements to allow calculation on a standard engineering workstation. Materials characteristics are mainly given by standard industrial codes and modeling hypothesis relies on elastic behavior of materials. Thermal BC consists in a thermal field beforehand calculated with a coupled approach between EDF computational fluid dynamics code (Code_Saturne) and its thermal code (Syrthes). Simulation results are presented. Attention is then focused on the evolution of the body-bonnet bolted flange joint tightening forces which are simulated during the thermal shock. Choices of modeling are addressed: for example, it is shown in this paper that the contact modeling hypothesis have to be discussed in order to allow good parts behavior description during transient.