Document: NRC Regulatory Guide
Document ID: c55ba6c5-aa2d-4ad6-aba2-2001e16524ab
Document Type: regulatory_guide
Title: Ultrasonic Testing of Reactor Vessel Welds During Preservice and Inservice Examinations (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1221/ML12216A015.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.150
CFR Part: 
CFR Title: 

Content:
tatic Versus Dynamic Reflector Responses With some automated systems, the DAC curve is manually established. In these cases, the signal is maximized by optimizing the transducer orientation toward the calibration holes. Subsequently, detection and sizing of flaws are based on signals received from a moving transducer where no attempt is made (or it is not possible) to maximize the signal even for significant flaws. This procedure neglects several sources of error introduced by the possible variation in signal strength caused by: (1) Differences between the maximized signal and the unmaximized signal. (2) Loss in signal strength due to the separation of the transducer from the metal surface because of the viscosity of the coupling medium (plan- ing effects). (3) Variation in contact force and transducer coupling efficiency. (4) Loss in signal strength due to structural vibra- tion effects in the moving transducer mount and other driving mechanisms. (5) Loss in signal strength due to the tilting caused by the mounting arrangement in some trans- ducer mounts. Because of the above, it would be advisable to establish the DAC curve under the same conditions as those under which scanning is performed to obtain data for detection and sizing. It would be acceptable to establish a DAC curve by maximizing signal strength during manual scans when signals are also maximized for flaw sizing. However, it would not be advisable to use manually maximized signals to establish the DAC curve when data are obtained later by mechanized transducers (where signals cannot be maximized) for the detection and sizing of flaws without adjustment for the potential error introduced. In these situations, an acceptable method would be to establish DAC curves using moving transducers or to establish correction factors that may be used to adjust signal strength. It would be prudent to use care and planning in establishing correction factors. For example, establishing a ratio between a dynamic and