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Detection of Thermal Fatigue Cracks in Stainless Steel Pipe: Application to the Inspection of RHRS line of Type N4/PWRYves BOUVERET,
Framatome Technical Center, ZIP, BP13, 71380 Saint Marcel Cedex, France, email@example.com.
Jean Michel TCHILIAN,
Framatome QR, 92084 Paris la Défense Cedex, France, firstname.lastname@example.org.
EDF / SQR Immeuble France-Evry, Boulevard de France BP 128, 91004 EVRY Cedex, France email@example.com.
Olivier de VAREILLES,
Intercontrôle, 13 rue du capricorne, SILIC 433, 94583 Rungis cedex.
The program of evaluations have been carried out namely by ultrasonic examinations of the components. A specific ultrasonic examination technique has been developed for the expertise of the damaged components. This technique has been improved through numerous examinations and validated by comparison with penetrant test examinations and metallographic examination, after cutting, of damaged zones. The second step has been to define the parameters, as type of transducers and reporting levels, applicable to the PSI and ISI of the new components in order to guarantee the performance of detection requested. The last step was the formal qualification of the PSI and ISI ultrasonic examination technique according to RSE-M 97 prescriptions.
The program of thorough inspections implemented by Framatome and Intercontrôle, was not limited to the only region comprising a 10" pipe elbow. The investigations were extended to the regions likely to be affected by the temperature variations. In addition to the 10" line, the inspections then covered the "no flow" RHRS line of 4" dia. and the 4" PCTS/RHRS junction.
Since 1998, initial inspection and 100 hours inspections have been carried out on the new designed items of the 10" and 4" line pipes. These checks were performed by ultrasonic testing according to the procedures prepared by the Technical Center of Framatome for the RHRS and PCTS lines. So, searching of the thermal stratification or crackling is mainly carried out using 45° refracted shear waves in half skip. Scanning is made in both directions parallel and normal to the line axes.
Searching of the cracks on the edge of the weld beads is made using 60°-angled shear waves in half skip.
For stainless steel RHRS and PCTS systems, the 2.25 and 3.5 MHz frequencies are used depending on the thickness and attenuation. Validation of these examination techniques was carried out by the Technical Center of Framatome on several mockups representative of the components and welds to be examined.
The qualification of "in-service" inspections is a "specific" qualification according to the RSE-M 97. Firstly, it consists in compiling a file containing the technical justification, an in-service inspection procedure and a qualification program describing the tests to be carried out on mockups representative of the components to be examined and containing artificial defects.
This file is supplemented by the inspection performance validation, after comparison of the results obtained by UT testing on coupons containing actual crackling defects and cracks on the bead edge (coupons taken from the defective components of the Chooz and Civaux N4 units) with the results of the destructive evaluations of these coupons.
When the qualification file was compiled, the qualification tests were carried out by Intercontrôle under the supervision of the Manufacturing Quality Division of EDF (SQR). The qualification file, qualification test results and a summary as well were presented by the Group of Laboratories of EDF (GDL) to the qualification commission in May 2000.
The qualification commission expressed a favourable opinion. The qualified procedures were implemented by Intercontrôle on the 4" RHRS of the Chooz B2 Unit during the first refueling shutdown.
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