Fast-track development of a TOFD inspection procedure for forged Steam Generator channel heads

Forestier, Yann; EDF-CEIDRE; France

Forestier, Y.; EDF-CEIDRE; France
Herault, C.; EDF-CEIDRE; France
Brun, P.; AREVA/Intercontrôle; France
De Roumilly, L.; EDF-CEIDRE; France
Martin, E.; EDF-CEIDRE; France

ID: ECNDT-0081-2018
Download: PDF
Session: Nuclear Industry 3
Room: H2
Date: 2018-06-13
Time: 15:20 - 15:40

This paper presents the work performed in order to develop, validate and apply a TOFD inspection procedure on-site, all of which were completed in a few weeks’ time.
This inspection was a consequence of the discovery of a carbon macro-segregation issue in steam generator channel heads (SG primary side) that could potentially have affected the mechanical properties of the material for SGs in several different NPP Units. The SGs are thick carbon steel spherically forged components, for which no in-service inspection had ever been performed. The inspection aimed at detecting postulated planar defects in the outer half of the channel heads.
The project deadline was that the first PWR reactors were scheduled for outage 1 month later. Therefore, an innovative approach was chosen and several actions were performed in parallel in order to reduce the development duration, most of which with a joint EDF-Framatome team:
• A wide selection of probes, holders and scanning equipment were tested;
• The capacities of these equipments were assessed on full-size mockups;
• Testblocks containing narrow EDM notches were manufactured;
• Computations with the CIVA UT software were also used to complement the experimental data.
Finally, the inspection procedure was finalized and a personnel training was carried out. This included customization of existing scanning equipment, in order to be adapted to the geometry of the component and to deal with some obstacles welded onto the scanning surface.
The first inspection and all the subsequent ones were performed successfully, requiring only minor adjustments to the procedure along the way. None of the inspected steam generators were found to contain the targeted defects.