Ultrasonic Flaw Sizing with Variable, Unknown Surface Geometry, 14-9556

Principal Investigators
Jay L. Fisher
Jim F. Crane
Richard F. Tennis

Inclusive Dates:  07/01/05 – Current

Background - Pressure-retaining welds in the primary system of nuclear power plants require periodic inspection to ensure that system integrity is maintained throughout the life of the plant. These inspections are usually performed during plant refueling outages using remote manipulators operating underwater to scan ultrasonic sensors over the welds and specialized data-acquisition systems to record the test data. A worldwide trend in the industry requires inspectors to demonstrate their ability to detect, locate, and characterize the size of defects found in plant components. Regulatory requirements for performance-based qualification tests have been implemented in stages to allow time to qualify their inspection equipment. The most recent inspection area to be included in the regulation is the weld joining the main recirculation loop piping to the reactor vessel. Unfortunately for the inspection service companies, the practice and test samples developed for this series have proven to be very difficult to inspect because of the irregular surface condition on the inside of the pipe where the ultrasonic probe is applied. Lack of adequate probe contact can defeat the test completely in some areas and partial contact or deviations of probe location from a nominal pipe surface can cause the data to be plotted incorrectly, thus misleading the inspector.

Approach - The current research includes a novel approach that uses surface profile measurements to calculate the focal law for a phased array-type probe at each location in the scan pattern. The resulting waveform data will be suitable for display using conventional data analysis software and free of the types of errors caused by irregular surface geometry. Experiments will include collecting data from conventional contact phased array, contact pulse echo, and immersion-type probes. These data will be manipulated using software to correct for measured surface geometry and the results compared with the adaptive phased array-type probe to determine the most effective method of dealing with irregular front surface conditions.

Accomplishments - Two new axes of motion have been added to our scan tank for scanning pipe samples. Software for the two new axes has been written and is currently under test. We are investigating methods for extracting A-scan waveform data from the phased array system that will be used to collect the adaptive beam scans. Three test blocks have been fabricated for collecting data that can verify that the surface correction software is working correctly.

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