High-Accuracy Defect Sizing for Nozzle Attachment Welds
T. Bloodworth, AEA Technology, Warrington, U.K.; L Johansson, Å. Pettersson, OKG Aktiebolag, Sweden
ABSTRACT
Inspection procedures for the detection, characterisation and high-accuracy sizing of defects in "Type J" nozzle attachment welds in Swedish BWRs have been developed. Type J welds are set-on nozzle-to-pipe attachment welds between the main recirculation pipe and related piping systems. The nozzles and the main recirculation pipe are made of ferritic steel with austenitic stainless steel cladding on the inner surface. The overall wall thickness of the nozzle is 30mm. The inspection uses an automated pulse-echo technique for the detection and length sizing of defects. Software for the display of complex geometry ultrasonic data is used to assist in data analysis. A novel automated ultrasonic TOFD technique is used to measure the through-wall height of defects. This technique deploys probes on both the nozzle and main pipe surfaces. The TOFD data for this complex geometry are then analysed using the CGTOFD software, to locate the origin of defect edge signals. The Qualification detection criterion for this inspection is the detection of defects 6mm´18mm (height´length) or greater. The required length measurement accuracy is ±14mm and the required through-wall height measurement accuracy is ±2.3mm. This last requirement is very demanding. The inspection procedures for detection and sizing passed Procedure Qualification when measured against the above criteria on an "open" test specimen. Data collection and analysis personnel have subsequently passed Personnel Qualification using "blind" specimens.
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission. Publisher:Woodhead Publishing Limited
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