In-Service Inspection of Nuclear Power Plants - gnssn - International ...

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This publication is no longer valid Please see http://www-ns.iaea.org/standards/ Eddy current examination is normally used for thin walled non-ferromagnetic materials, e.g. heat exchanger tubing, to detect wall thickness thinning, dents, etc. 5.3.3. Requirements for volumetric examination The examination should be described in a written procedure as specified in Section 4.4.1. This procedure should include: — scope of application — qualifications of examination personnel — examination of the visual acuity of examination personnel — surface preparation — examination techniques (kind of equipment) — equipment calibration — calibration blocks — remote handling devices — acceptance standards — documentation and reports. 5.3.4. Performance of volumetric examination The surfaces to be examined should be prepared according to Section 4.4.2.2 of this Manual. Because there are various application possibilities of the volumetric examination method, it is recommended that in addition to the items listed in Section 5.3.3, specific items, depending on the examination technique, be defined for an inspection area. These items can be: (1) Ultrasonic examination 34 Weld types and configurations to be examined: — the surface or surfaces from which the examination is performed; — couplant; — techniques, orientation of transducers, angles and modes of wave propagation in the material; — transducer characteristics; — specific search units (e.g. wedges, shoes, saddles, cables); — ultrasonic instrument type and characteristics; — calibration technique; — equipment settings; — directions, extent and speed of scanning; — data to be recorded and recording method.
This publication is no longer valid Please see http://www-ns.iaea.org/standards/ (2) Radiographic examination Weld types and configuration to be examined: — the surface or surfaces from which the examination is performed; — radiographic source used, including size, maximum X ray voltage; — geometrical configuration (maximum distance between material surface and film, minimum distance between source and film, film position); — type and designation of film and intensifying screens; — type and location of image quality indicator and quality level required; — viewing screens, light intensities; — radiographic density limitations; — measures to avoid backscatter radiation; — number of required films, e.g. a circumferential weld; — geometrical unsharpness limitation. (3) Eddy current examination Components or parts of components to be examined: — eddy current examination : technique (absolute or differential mode); — single frequency or multiple frequencies; — eddy current examination equipment; — coils and cables; — calibration standards; — equipment settings; — examination speed; — data recording equipment. For better reproducibility of ultrasonic examination, a periodical check of the most important equipment parameters, including the sound field characteristics of the transducers, is recommended. The beam angles should be optimized so that surface defects as well as volumetric defects can be detected. In some Member States, the examination calibration is performed with the help of a cylindrical surface of drilled holes establishing the 'distance-amplitude-correction' (DAC) curve. Some other Member States use the 'Abstandsverstarkungsgrosse' (AVG) diagram, which is based on the comparison of the echo height of flat bottom holes in calibration blocks. To enable comparison with the following ISIs, the calibration method, once selected, should be retained or, if changed, a correlation with the previous one should be established to the extent practical. To facilitate the interpretation of indications from the inaccessible surface, exact drawings and knowledge of the surface conditions are necessary. Wall thickness measurements are also useful. 35
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