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:
ts 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 defect depends on the proportion of the ultrasonic beam reflected back to the probe. The reflection behavior of a planar defect, which largely depends on the incident beam angle when a single search unit is used to characterize the flaw, is thus a decisive factor in flaw estimation. The larger the size of a planar defect, the narrower is the reflected sound beam. The narrow reflected sound beam makes the flaw very difficult to detect in most cases (unless the beam angle is right). 6 ' 7 6"Probability of Detecting Planar Defects in Heavy Wall Welds by Ultrasonic Techniques According to Existing Codes," Dr. Ing. Hans- Jurgen Meyer, Quality Department of M.A.N., Nurnberg, D 8500 Nurnberg 115. 7"Reflection of Ultrasonic Pulses from Surfaces," Haines and Langston Central Electricity Generating Board, U.K. (CESB) Report Number RD 18/N4115. I 4 I 1.150-4 Therefore, the beam angles used to scan welds should be optimized and should be based on the geometry of the weld/parent-metal interface. At least one of these angles should be such that the beam is almost perpendicular (±15 degrees to the perpendicular) to the weld/parent-metal interface, unless it can be demonstrated that large (Code- unacceptable) planar flaws unfavorably oriented, parallel to the weld-metal interface, can be detected by the UT tech- nique being used. In vessel construction, some weld preps are essentially at right angles to the metal surface. In these cases, use of shear wave angles close to 75 degrees is not recom- mended. Two factors would make the use of shear wave angles close to 75 degrees inadvisable, - first, the test distances necessary become too large resulting in loss of signal, and second, the generation of surface waves tends to confuse the interpretation of results. In these cases, use of