Challenges and Capabilities for Inspection of Cast Stainless Steel Piping
Studies conducted at the Pacific N¬orthwest National Laboratory (PNNL) in Richland, Washington, have focused on developing and evaluating the reliability of nondestructive examination (NDE) approaches for inspecting coarse-grained, cast stainless steel reactor components. The objective of this work is to provide information to the United States Nuclear Regulatory Commission (US NRC) on the utility, effec¬tiveness and limitations of NDE techniques as related to the inservice inspec¬tion of primary system piping components in pressurized water reactors (PWRs). This paper describes results from recent assessments built upon early work with low frequency ultrasonic testing (UT) coupled with synthetic aperture focusing technique (SAFT) signal processing, and has subsequently evolved into an approach using low frequency phased array technology as applied from the outer diameter surface of the piping. In addition, eddy current examination as performed from the inner diameter surface of these piping welds is also reported. Cast stainless steel (CSS) pipe specimens were examined that contain thermal and mechanical fatigue cracks located close to the weld roots and have inside/outside surface geometrical conditions that simulate several PWR primary piping weldments and configurations. In addition, segments of vintage centrifugally cast piping were also examined to understand inherent acoustic noise and scattering due to grain structures and determine consistency of UT responses from different locations. The advanced UT methods were applied from the outside surface of these specimens using automated scanning devices and water coupling. The phased array approach was implemented with a modified instrument operating at low frequencies and composite volumetric images of the samples were generated with 500 kHz, 750 kHz, and 1.0 MHz arrays. Eddy current studies were conducted on the inner diameter surface of these piping welds using a commercially available instrument and a cross point probe design operating at a frequency of 250 kHz. Results from the laboratory studies indicate that 500 kHz phased array methods are capable of detecting flaws greater than 30% through-wall in the cast specimens. Length-sizing of flaws is possible, but no diffracted signals could be observed to support time-of-flight depth sizing. The work with eddy current examinations on the inner diameter surface indicate that, while certain cast austenitic microstructures provide excessive background noise due to permeability variations, surface-breaking flaws are quite easily detected. This work was sponsored by the U.S. Nuclear Regulatory Commission under Contract DE-AC06-76RLO 1830; NRC JCN Y6604; Mr. Wallace Norris, NRC Project Monitor.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 966019
- Report Number(s):
- PNNL-SA-55129; 401001060; TRN: US0904015
- Resource Relation:
- Conference: Proceedings of the 19th International Conference on Structural Mechanics in Reactor Technology, August12-17, 2007, Toronto, Canada, Paper #O-02/3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
36 MATERIALS SCIENCE
ACOUSTICS
APERTURES
BACKGROUND NOISE
DEFECTS
EDDY CURRENTS
FOCUSING
PERMEABILITY
PROBES
PWR TYPE REACTORS
REACTOR COMPONENTS
REACTOR TECHNOLOGY
RELIABILITY
SCATTERING
SIZE
STAINLESS STEELS
ULTRASONIC TESTING
Cast Stainless Steel Welds
Low Frequency Phased Array
Eddy Current Testing