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:
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 static mode under laboratory conditions using a precision transducer drive and stiff mounting may have very little in common with the transducer mounting and traverse condi- tions of the actual examination setup. If correction factors are to be used, it would be worthwhile to build either full-scale mockups or consider the variation of all the important parameters in a suitable model taking into 1.150-3 consideration scaling laws on variables such as mass, vibration, and stiffness constants. 'It would be advisable to confirm the scaling law assumptions and predictions for vibration and viscosity effects before correction factors are used for setting scanning sensitivity levels. Differences in the curvature and surface finish between calibration blocks and vessel areas could change the dynamic response, so it may be advisable to establish correction factors between dynamic and static responses from the indications that are found during examination. This would avoid the difficulties associated with establishing a dynamic response DAC curve and still take all the factors into consideration. e. Secondary DAC During some manual scans, the end point of the DAC curve may fall below 20 percent of the full screen height. When this happens, it is difficult to evaluate flaws on the 20 percent and 50 percent DAC basis in this region since the 20 percent and 50 percent DAC points may be too close to the baseline. To overcome this difficulty, it is advisable that a secondary DAC curve using a higher-gain setting be developed so that 20 percent and 50 percent DAC points may be easily evaluated. For this purpose, it is advisable that the gain be increased sufficiently to keep the lowest point of the secondary DAC curve above 20 percent of screen height. The secondary DAC curves need