Ultrasonic Examination of a CVCS Weld

The anisotropic, heterogeneous and coarse granular structures of austenitic stainless steel welds may lead to important disturbances of the ultrasonic propagation : beam skewing and splitting, attenuation, backscattering and spurious echoes. Numerous studies were undertaken by EDF R&D and CEA for a few years to study these disturbances and to improve the ultrasonic NDT in nuclear applications. This paper presents a laboratory study on the ultrasonic examination of the branch pipe weld connecting the Chemical and Volume Control System (CVCS) and the primary coolant piping of PWR circuits. Both experimental and theoretical approaches are used in this work, which helped to set up the methodology for modelling ultrasonic inspection of an austenitic stainless steel weld, presented in this conference [1]. Two theoretical approaches are presented : a FEM code, ATHENA, developed by EDF, and a semi-analytical code integrated in the CIVA simulation platform, developed by CEA. These codes simulate the propagation of the ultrasonic beam in the weld and calculate the defect/beam interaction. Experimental tests are performed on a plane mock-up representative of a CVCS weld in terms of material and welding process. The geometrical effect is not studied here. Experimental cartographies of the transmitted field through the weld were acquired for several orientations of the probe. These cartographies are compared to computed fields. The responses of defect embedded in the weld structure are also presented and compared to experimental measurements. In particular, the influence of the wave characteristics on the detection and on the characterization of the defects is evaluated. 1. CONTEXT AND OBJECTIVES EDF R&D has launched in collaboration with CEA a consistent research program on ultrasonic inspection of austenitic stainless steel welds. This program deals with the comprehension of the structure effect on the NDT performances [2,3]. As far as structural effects are concerned, the main ultrasonic disturbances are: a strong anisotropy of the properties of elasticity which, coupled with the heterogeneity of the orientation of the grains, can produce significant deviation, splitting and distortion of the beam; an important scattering of the ultrasounds by the grains involving an attenuation and a structural noise. This paper presents a laboratory study on the ultrasonic examination of the branch pipe weld connecting the Chemical and Volume Control System (CVCS) and the primary coolant piping of PWR circuits. The objectives are to demonstrate the ultrasonic controllability of a CVCS weld, to improve the understanding of the ultrasonic disturbing phenomena and to provide technical data in support of the development and the qualification of an NDT process. This work is based on both experimental analyses on welded mock-ups and the use of modelling tools (ATHENA 2D code, CIVA software) which allow realistic simulation of the phenomena of propagation in complex mediums. The modelling work is based on a methodological approach whose aim is to provide a realistic description of the austenitic weld. Details on this methodology can be found in an other paper of this conference [1]. For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=70 6th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components October 2007, Budapest, Hungary