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:
or these holes are polished, this fact should be recorded for consideration if a review of the UT data becomes necessary at a later date. 3. NEAR-SURFACE EXAMINATION AND SURFACE RESOLUTION Sound beam attenuation in any material follows a decaying curve (exponential function); however, in some cases the reflection from the nearest hole is smaller than the reflection from a farther hole. This makes it difficult to draw a proper DAC curve. In such cases, it may be desirable to use a lower frequency or a smaller transducer for flaw detection near the beam-entry surface to overcome the difficulty of marginal detectability. Near-field effects, decay time of pulse reflections, shadow effects, restricted access, and other factors do not permit effective examination of certain volume areas in the component. To present a clear documentation and record of the volume of material that has not been effectively examined, these volume areas need to be identified. Recom- mendations are provided to best estimate the volume in the region of interest that has not been effectively examined, such as volumes of material near each surface (because of near-field effects of the transducer and ring-down effects of the pulse due to the contact surface), volumes near interfaces between cladding and parent metal, and volumes shadowed by laminar flaws. 4. BEAM PROFILE Beam profile is one of the main characteristics of a trans- ducer. It helps to show the three-dimensional distribution of beam strength for comparing results between examinations and also for characterizing flaws. The beam profile needs to be determined and recorded so that comparisons may be made with results of successive examinations. 5. SCANNING WELD-METAL INTERFACE The amount of energy reflected back from a flaw is dependent on its surface characteristics, orientation, and size. The present ASME Code procedures rely on the amplitude of the reflected signal as a basis for judging flaws. This means that the size estimation of a