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:
, - 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 alternative volumetric nondestructive examination (NDE) techniques, as permitted by Subarticle IWA-2240, Section XI of the ASME Code, should be considered. Alternative NDE techniques to be considered may include high-intensity radiograph or tandem-probe ultrasonic examination of the weld-metal interface. To avoid the possibility of missing large flaws, particularly those that have an unfavorable orientation, it is desirable that the back reflection amplitude, while scanning with a straight beam, be monitored over the entire volume of the weld and adjacent base metal. Any area where a reduction of the normal back-surface reflection amplitude exceeds 50 percent should be examined by angle beams in increments of ±15 degrees until the reduction of signal is explained. Where this additional angle beam I examination is not practical, it may be advisable to consider examining the weld by a supplementary volumetric NDE technique. 6. SIZING The depth or through-wall dimension of flaws is more significant than the length dimension, according to fracture mechanics analysis criteria. Using the single-probe pulse-echo technique, it is possible, depending on flaw orientation, that some large flaws may not reflect much energy to the search unit. 6 Because of this possibility, the depth dimen- sion of the flaw should be conservatively sized unless there is evidence to prove that the flaw orientation is at right angles to the beam. It is recommended that indications that are asso- ciated with through-thickness flaws and do not meet Code- allowable criteria or criteria recommended in this guide be sized at 20 percent DAC as well as at 50 percent DAC. In certain cases, it is possible for various reasons that a flaw would not reflect enough energy to the search unit to make the