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This publication is no longer valid Please see http://www-ns.iaea.org/standards/ — the measures to be taken after the examination to remove all remnants of examination materials which could be detrimental to the installation; — the relevant recording, evaluation and acceptance standards as applicable; — the detailed description of the evaluation of the examination results; — the limitations; — the detailed description of reporting the performance and the results of the ISIs. 4.4.2. Surface preparation of the components Surface conditions as well as surface roughness or surface evenness and cleanliness are dependent on the examination method and should be described in the specific examination specification. Generally all surfaces should be clean from scale, loose paint, dirt, burrs, spatter, slag or other conditions that will interfere with the test results. Specific surface preparation measures are necessary for surface and volumetric examinations. 4.4.2.1. Surface examination method Satisfactory results are usually obtained when the surfaces are in the aswelded, as-rolled, as-case, or as-forged conditions. However, surface preparation by grinding or machining may be necessary where surface irregularities could mask indications due to discontinuities. Shot peening must not be used to prepare surfaces for surface examination. Prior to surface examination, the surface to be examined and all adjacent areas should be dry and free of all dirt, grease, lint, scale, welding flux and spatter, oil, or other extraneous matter that could interfere with the examination. Cleaning may be accomplished using detergents, organic solvents, descaling solutions, paint removers, vapour degreasing, or ultrasonic cleaning methods. The surface roughness should be less than Ra = 10 fim. For magnetic particle examination a colour layer with a thickness of less than 0.04 mm is normally negligible. If indications appear which cannot be distinguished, a better surface condition or another non-destructive technique may be recommended, if they are realistic. 4.4.2.2. Volumetric examination method (1) Radiographic examination 22 (a) Base materials Surfaces should satisfy the requirements of the applicable materials specifications, with additional conditioning, if necessary, by any suitable
This publication is no longer valid Please see http://www-ns.iaea.org/standards/ process to a degree that surface irregularities cannot mask or be confused with discontinuities. (b) Welds The weld ripples or weld surface irregularities on both the inside (where applicable) and outside should be removed by any suitable process to such a degree that the resulting radiographic image cannot, owing to any irregularities, mask or be confused with the image of any discontinuity. (c) Surface finish The finished surface of all butt welded joints should be flush with the base material or should have reasonably uniform crowns, with reinforcement to exceed the specification limits. (2) Ultrasonic examination Normally the surface roughness should be less than Ra = 10 /im. The surface should be sufficiently even that the selected ultrasonic transducer has a proper coupling with the inspection surface. The necessity of grinding a weld surface depends on the width of the inspection area, the wall thickness, the defect orientation and the beam angle. After machining or grinding a weld surface a marking of the former weld shape may be helpful to distinguish between realistic indications and geometrical shape indications. If both an ultrasonic and a surface examination method are used at the same inspection area, the surface examination should be done before the ultrasonic examination because of the use of liquid couplings which could mask surface indications. 4.4.3. Reproducibility The aim of ISI is to show if a component or part of a component is affected by operating conditions. The comparison of the examination results shows if a new defect has developed or if an indication from an earlier examination has changed. To allow such a comparison between pre-service inspection and the inspections within the different inspection intervals a good reproducibility has to be guaranteed. In some cases comparison of examination results is the only way to evaluate an indication. 23
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