Advanced NDE Techniques for Reliable Crack Inspection and Fitness-for-Service Assessments

Reliable and accurate NDE (Non-Destructive Evaluation) techniques are required to conduct FFS (Fitness-For-Service) assessments for crack type flaws in equipment. FFS assessments rely on certain flaw detection and flaw sizing assumptions which can only be provided through NDE. The detection and sizing provided by the NDE work is highly dependent on both inspection methodology (e.g., operator, equipment, and procedure) as well as the specific component and application (e.g., part thickness and geometry, flaw type, damage mechanism, etc.). Therefore, the accurate determination of these detection and sizing assumptions requires thorough consideration, modeling, assessments, and determination by NDE specialists. This paper will describe factors that affect flaw detection and sizing results by NDE, the use of synthetic flaws to assess and improve NDE performance, the verified performance of advanced NDE techniques on natural flaws, and the integration of NDE performance results with FFS assessments.

Technical Basis for a Flaw Tolerance Option for Code Case N-770-1 for Large Diameter Cold Leg Piping to Main Coolant Pump Welds, With Obstructions

An extensive series of evaluations have been performed on the Alloy 82/182 dissimilar metal butt welds located at the safe end regions of the CE designed reactor coolant pump suction and discharge nozzles. These nozzles present inspection coverage challenges, which hinder the likelihood of obtaining the required inspection coverage of MRP-139, and the successor document, ASME Code Case N-770. Furthermore, the geometry of the region also contributes to the difficulty of performing standard mitigation techniques. However, these nozzle regions operate at cold leg temperatures, nominally 550°F, and have a very high resistance to the potential for PWSCC, and a low predicted crack growth rate, if such a flaw were to exist in the region. This leads to the suggestion that the required inspection regimen may be too strong for these regions, and the study described herein was structured to investigate that possibility and develop a technical basis for proposing changes to inspection requirements consistent with the flaw tolerance of the region. Specifically, changes to Code Case N-770 are proposed herein, to take advantage of the flaw tolerance of the region. These proposed changes are described in this paper, and the technical basis for them is described in the remainder of the paper. The technical basis rests on three complementary findings: 1. The probability of a flaw existing or initiating in this region is very low; 2. There is a significant margin between the size flaw which would leak at a detectable rate, and the size flaw which would cause the pipe to fail. This provides a significant level of defense in depth for the region; and 3. The flaw tolerance of the region, for both axial and circumferential flaws, is very high, as measured by the size flaw which could grow to the Section XI allowable flaw size for either flaw type.

Research on Automatic Flaw Classification and Feature Extraction of Ultrasonic Testing

In this paper, Lifted Wavelet Transform (LWT) and BP neural network are used for automatic flaw classification of pipeline girth welds. LWT is proposed to extract flaw feature from ultrasonic echo signals, ideally matched local characteristics of original signal and increasing the computational speed and flaw classification efficiency. After extracting features of all flaw echoes, a feature library is constructed. A modified BP neural network is followed as a classifier, trained by the library. When feature of any flaw echo is extracted and sent to BP network, flaw type is the output, realizing automatic flaw classification. Experiment results prove the proposed method, LWT with BP neural network, is more fit for automatic flaw classification than traditional methods.

Characterization of Mechanical Reliability of Silicon Nitride Microturbine Rotors

This paper summarizes the recent results on component characterization efforts carried out to verify the mechanical reliability of SN237 and SN281 silicon nitride microturbine rotors manufactured by Kyocera. Mechanical properties of biaxial discs machined from airfoils of microturbine rotors were evaluated by a ball-on-ring test technique. Results showed that the mechanical properties of samples from airfoils with as–processed surfaces exhibited lower characteristic strength than those machined from the hub region with as-machined surfaces. The differences in mechanical performance and reliability between asprocessed components and simple-shaped test coupons appear to arise mainly from differences in strength limiting flaw type and population.