Inspection Qualification II

Transcription

1 Inspection Qualification II The Benefits of Technical Justification in the Inspection Qualification of Nozzle Inner Radius R. Martínez-Oña, J. Sánchez, R. Jiménez, Tecnatom, Spain INTRODUCTION Technical justification plays an important role in the qualification of non destructive examinations. The different types of technical justifications and their contents have been described in the ENIQ Methodology and recommended practices. The main idea of ENIQ approach to qualification is the use of a combination of technical justification and test piece trials to provide confidence in inspection performance. The technical justification compiles all the supporting evidence for the adequacy of an inspection and therefore minimises the reliance on test pieces, it can also allow generalising specific test piece data very effectively and identify defect worst case among other questions. For these reasons, using technical justifications can produce more effective qualification processes. The objective of this paper is to present the benefits of technical justifications in the inspection qualification of complex components. This will be done by means of the description of the nozzle inner radius technical justifications carried out in the framework of the Inspection Qualification Spanish Methodology. The physical reasoning of essential variables and the evidence to support the chosen procedure are ones of the most important information that should include the technical justification. In addition to the experimental data, the evidence could also include theoretical assessment, prediction by modelling, coverage analyses, and parametric studies among others; the availability and use of these studies contributes to reduce the costs of the experimental part and increase the reliability of the obtained results. This is especially of interest when the availability of mock ups is scarce and their costs are expensive due to the geometry and configuration of the component. In this paper a description of the ENIQ technical justification content is first outlined. It follows the discussion of nozzle inner radius technical justifications prepared for GRUVAL (the Spanish Validation Group) inspection qualifications, and description of the coverage, complementary modelling and parametric studies, which has been prepared for supporting the new technical justification based on the first one. The examples quoted show the benefit of using technical justifications. PURPOSES AND CONTENTS OF TECHNICAL JUSTIFICATIONS ENIQ methodology document defines a technical justification as a collection of all the information that provides evidence about the reliability of an NDT technique as applied to a specific component [1]. The purpose of the technical justification is: To overcome the limitations of the limited number of test pieces that can be used by citing all the evidence which support an assessment of the capability of the NDT system to perform to the required level and hence provide a better defined confidence in the inspection. To complement and to generalise any practical trials by demonstrating that the results obtained on the specific defects in the test pieces would equally well have been obtained for any other of the possible defects. To provide a technical basis for designing efficient test piece trials. To provide a technical basis for the selection of the essential parameters of the NDT system and their valid range. The three most common applications of technical justifications are to justify the use of: inspection procedures, test pieces and defect populations, and inspection equipment. However, there are cases where it is desired to extend an existing qualification to a new situation, for example from one component geometry to another or from one component material to another material structure [2]. The technical justification can be composed of the following main sections:

2 Input information regarding component to be inspected, postulated defects, and overview of inspection system. Analysis of influential parameters to identify the essential variables. Physical reasoning, qualitative assessment and justification of the main inspection parameters selected. Supporting evidence including: Prediction of theoretical modelling, Experimental studies, test results, field experience, Parametric studies. The flow chart showing the interactions of these technical justification (TJ) sections is summarised in Figure 1. In the example that follows will be shown the development of a new TJ based on an existing TJ and specific supporting evidence such as modelling (ray tracing coverage, pulse echo response) and parametric studies. This will make clear the benefits of TJ by reducing the availability of mock-ups and generalising the results of practical trials. Introduction Input information Analysis of influential parameters Physical reasoning Prediction by modelling Experimental evidence Parametric studies Conclusions Figure 1 - Scheme of the main contents for technical justification as recommended by ENIQ SPANISH QUALIFICATION METHODOLOGY AND STUDY CASE As it was presented in the 6 th edition of this series of conferences, the Spanish Qualification Methodology of inspection systems is based on the ENIQ European Methodology and takes into consideration, according to the Spanish Law, the requirements of the country of origin of the nuclear power plant [3]. The areas and components subject to qualification are the ones established according to ASME Code Section XI; one of these is the Appendix VIII Supplement 5: Nozzle Inner Radius

3 Section. In relation to this area, according to the existing NPPs, two qualification groups have been defined: Nozzle inner radius (IR) without cladding, and Nozzle inner radius with cladding. Taking into account the geometry of this component, bulky and complex, it is difficult and expensive to have available test mock-ups to obtain all the necessary experimental evidence for the two qualification groups; for this reason, to develop the corresponding TJ we have made use of prediction by modelling and parametric studies as supporting evidence as much as possible. Input data A Qualification Objectives report for each qualification group is prepared. It contains input data information partly presented as tables; one of these tables addresses the component influential variables and other one the defect influential variables. In the Tables 1 and 2 are summarised the component and defect influential variables of the two qualification groups that are the object of our analysis. The main differences between the two qualification groups mentioned above are: nozzles have the same morphology but different geometrical dimensions and the nozzles of one group have a cladding layer and the nozzles of the other group do not have a cladding layer. Thereby the approach followed, to prepare the TJs required, has been: 1) to elaborate the TJ of the group of nozzles without cladding, based on this, 2) to perform modelling and parametric studies, and 3) to complete the TJ of the group of nozzles with cladding. Variable Group Nozzle IR without Group Nozzle IR with cladding cladding Surface roughness < 250 µinches < 125 µinches Nozzle thickness mm mm RPV thickness 139 mm mm Nozzle OD mm mm RPV OD 5848 mm mm Nozzle inner radius mm mm Nozzle outer radius mm mm Cladding thickness -- 4 mm Table 1 - Component influential variables Variable Group Nozzle IR without Group Nozzle IR with cladding cladding Orientation Axial Axial Type Postulated Postulated Depth 6.4 mm 6.4 mm Position Surface breaking Surface breaking or under cladding Tilt ±10 ±10 Skew ±10 ±10 Roughness No No Table 2 - Defect influential variables

4 To accomplish this, the following main steps were carried out in our study: 1) Inspection volume coverage of a group of nozzles without cladding and with dimensions similar to an existing nozzle test mock-up named N5. This would allow us to define the ultrasonic (US) inspection techniques. 2) Inspection volume coverage of group of nozzles with cladding and with different dimensions than the previous group. This would allow us to determine the range of applicability of the technique. 3) Experimental evidence from test specimen containing realistic defects. This would allow us to determine the capability of the inspection techniques for the geometry under study. 4) Parametric study to assess the cladding influence. This would allow determining the capability of the inspection techniques for the cladding configuration. Coverage of inspection volume of nozzles without cladding Coverage of inspection volume is a difficult question to assess when the component has a complex geometry as is the case of the nozzle inner radius (see Figure 2). The assessment study was carried out with Tecnatom Ray Tracing program. The coverage map shows the angle of incidence at each point of the inner radius surface (see Figure 3); the colour of each point indicates the angle of incidence according to the colour code given in the figure. The study concluded there is 100% coverage. A B C E D F Figure 2 - N5 nozzle geometry and inner radius inspection volume Figure 3 - US inspection coverage map in N5 nozzle IR without cladding

5 Figure 4 - US inspection coverage map of nozzle IR with cladding Coverage of inspection volume of nozzles with cladding To extend the applicability of the experimental evidence, an inspection volume coverage study of the nozzles with cladding has been carried out using the Ray Tracing program explained in section above. The nozzle configuration with the most limitative dimensions has been simulated and analysed. The results are presented in figure 4; they show, applying the same inspection variables than before, that the required volume is covered. Other essential variable that would be assessed, when the component geometry dimensions varies, is the scanning path overlap between the scan lines. The most critical scanning path sector of the nozzle inner radius examination is the one along the outer radius surface due to its curvature; this is assessed for both nozzle groups with and without cladding. The scanning path overlap for N5 nozzle assures a good coverage between scan lines as shown in Figure 5 and corroborated by the experimental results. A similar assessment for N6 nozzle with cladding and with the dimensions more far apart of N5 also demonstrates a good coverage (see Figure 5b) R80 R65 R R R30 Figure 5 - Scanning path overlap between scan lines for N5 nozzle and N6 nozzle. The dimensions of these nozzles are in the upper and lower limits of the dimension range Experimental evidence This complement the coverage studies and provides support for the detection and sizing techniques. The test mock-up includes 37 realistic and mechanised implanted defects distributed in the inner

6 E7R 15 E8R E6R E9R E11R E1R E5R E10R 16 E12R E2R E4R 17 E3R radius and nozzle body areas that represent the worst case locations (see Figure 6). The ultrasonic inspection techniques were defined according to the results provided by the coverage studies. The experimental evidence results were the following: a) Detection: 100% of defects detected, b) Length sizing: the root mean squared error in each one of the four zones (± 18.3mm, ± 9.8mm, ± 7.5mm and ± 6.2mm) is less than the specified error RMS (± 19.1mm), c) Depth sizing: the root mean squared error in each one of the four zones (± 1.2mm, 0mm, ± 1.4mm and ± 1.5mm) is less than the specified error RMS (± 3.8mm). In figure 7 is shown an example of a defect B and A-scan located in the inner radius curve part. 0º Zone 1: IR curve part Zone 2: IR straight part Zone 3: Nozzle body next to IR 270º 90º A B Zone 4: Nozzle body next to S-E C E D F 180º Figure 6 - Nozzle test mock-up four zones where the defects are implanted and distribution of defects in zone 1 Defect tip signal Inner radius surface Defect corner signal Reflection signal Diffraction signal Figure 7 - B and A-scan of a defect located in the N5 mock-up inner radius area Assessment of cladding influence The objective of the parametric study carried out is to characterise the effect of cladding on the ultrasonic signals that are relevant to the applied examination techniques. The US technique is aimed to detect and size defects equal or larger than the specified in the input data table. The technique

7 investigates all signals that are above the noise level and satisfy certain conditions such as location, echo dynamic evolution, and persistence. We have studied signals coming from defects of different depths in test pieces without and with cladding and we have also modelled their responses with CEA s CIVA program. As example, in Figure 8a could be shown the response of a 6mm depth surface breaking defect in a test block without cladding with a probe of 2.25MHz, 45 and in Figure 8b its expected response by modelling. Accordingly, in Figure 9a is presented the B-scan of a surface breaking defect in a test block with cladding and in Figure 9b the modelled B-scan; the defect is 11mm depth, the cladding thickness is 5mm and the probe equal to the one in previous example. The results indicate that the modelling helps to understand and generalise the test data, the technique is able to characterise, detect and size surface breaking defects through the cladding larger than the specified in the input data table. These results together with the previous finding allow us to elaborate the new TJ of nozzles group with cladding based on these studies and without the need of making use of test mock-up with cladding. Inner radius surface Figure 8 - B-scan of a surface breaking defect of 6mm depth in a test block without cladding, actual data, simulated data Figure 9 - B-scan of a surface breaking defect of 11mm depth in a test block with 5mm cladding, actual data, simulated data

8 CONCLUSIONS Technical justification plays an important role in the qualification of non destructive examinations. By compiling all the supporting evidence available, TJ minimises the reliance on test pieces and it also allows generalising specific test piece data very effectively. A study case of the nozzle inner radius technical justifications carried out in the framework of the Inspection Qualification Spanish Methodology have been analysed. By means of using theoretical assessment such as prediction by modelling, coverage analyses, and parametric studies, a new technical justification has been elaborated without the need of making use of new and expensive test mock-ups. These studies contribute to reduce the costs of the experimental part and increase the reliability of the obtained results. The example quoted shows the benefit of using technical justifications. REFERENCES (1) European Methodology for Qualification of Non-Destructive Testing, 2nd issue, ENIQ Report nr. 2, EUR EN, (2) ENIQ Recommended practice 3: Strategy document for technical justification, 1 st issue, ENIQ Report nr. 5, EUR EN, (3) Martínez-Oña R, Qualification Methodology of Inspection Systems at Spanish NPPs: Status and some Examples, Proc. 6 th Intl. Conf. on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components, EUR EN-2008.