NDTnet 1998 Aug, Vol.3 No.8

Abstract

During the last few years a new repairing technology on austenitic steam generator (SG) tubes for nuclear power plants was developped. With the pepairing technique also an inspection technique was commanded. This was the begin of the sleeving technique and with it a chance for remote field eddy current technique.

It was a demand to repair plugged SG-tubes (022xl,2mm) to get them back for heat exchange. In Germany the sleeving technique was developped simultaneously by Siemens KWU and ABB Reaktor. While ABB first used the wig-welding and then the thermo-sleeve technology, KWU started with the Laser welding technology. Common technology is, that short sleeve tubes were inserted into the area of defect SG-tubes and the upper and lower ends of the sleeves were expanded. In the expansion zones both tubes then can be welded together.

With the KWU technology the welding is done by laser. To ensure that the weldings were good and without flaws and the welding widths were sufficient (demand: width larger than 0,8mm), the weldings have to go through a manufacturing-inspection. This inspection first was done with ultrasonic, but it showed, that on good weldings the inner surface of the weld were uneven and total reflection resulted with using ultrasonic inspection. Using the RFEC-technique the material changes in the weld area could be descibed very well on small as well on extented weldings.

The new RFEC-Technique uses 2 frequencies, the 2 frequencies will be mixed (least square fit method) to establish the welding width between the sleeve and the steam generator tube.The RF-results were compared with absolute results after sleeve probe destruction. It showed, that an accuracy of 0,10 to 0,l5mm could be reached. The RFEC-method was qualified in 1997 in Germany. The first inservice inspection was performed in February 1997 at a Nuclear Power Plant in Germany.

It will be tamed about the sleeving technology of laser weldings. The RFEC-System as well as Data Evaluation Methods will be discussed and some examples with different weldings will be shown. Finally new applications will be introduced.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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