Feature-based imaging for cast stainless steel components: 1987 and 1988 field examinations: Final report
Digital-based inspection systems were used for the ultrasonic examinations and analysis of the hot-leg elbow in the Trojan Nuclear Power Plant in 1987 and 1988. This was the first time advanced systems were utilized during successive plant outages to monitor inspection data. The hot-leg elbow is made of statically cast stainless steel known for its mechanical strength and corrosion resistance. However, it presents unique difficulties in ultrasonic inspection because the large grain sizes can cause severe signal attenuation and beam redirection. The 1987 examination was authorized by Portland General Electric of Portland, Oregon, based on a study in 1985 which revealed that the hot-leg elbow could have experienced maximum strain and loading conditions because of steam generator snubber lockup. Seven indications were discovered during this examination; none of them was larger than the expected grain size in this material. The data were digitally processed at the EPRI NDE Center utilizing a personal computer based system that was integrated to other commercial systems and capable of feature-based imaging. Bandpass filtering and spatial averaging were found to increase signal-to-noise-ratio by as much as a factor of 2, i.e., 6 decibels. The hot-leg elbow was reexamined in 1988 using similar apparatus and inspection procedures. In addition to the seven 1987 indications, three more indications were discovered. These were determined to be in the midwall region. The largest of all the indications as reported by the inspection vendor was comparable to the average grain size, approximately 0.50 inch. The data were digitally processed at the EPRI NDE Center using similar techniques. Feature-based imaging of 1987 and 1988 inspection data made it possible to evaluate elbow conditions more reliably. 15 refs., 52 figs., 2 tabs.
- Research Organization:
- Electric Power Research Inst., Palo Alto, CA (USA); EPRI Nondestructive Evaluation Center, Charlotte, NC (USA)
- OSTI ID:
- 6768176
- Report Number(s):
- EPRI-NP-6177; ON: TI89006678
- Country of Publication:
- United States
- Language:
- English
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