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:
valuated. 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 not be generated unless they are required. If electronic DAC is used and amplitudes are maintained above 20 percent of full screen height, a secondary DAC would not be necessary. f. Component Substitution A calibration check should be made each time a component is put back into the system to ensure that such components as transducers, pulsers, and receivers were not damaged while they were in storage. This will ensure elimination of the error band and mistakes in resetting the various control knobs. g. Calibration Holes Comparison of results between examinations performed at different times may be facilitated if the same equipment is used and if the reflections from growing flaws can be compared to the same reference signal. Reference signals obtained from a calibration block depend on, among other things, the surface roughness of the block and the reflector holes. Therefore, these surfaces should be protected from corrosion and mechanical damage and also should not be altered by mechanical or chemical means between successive examinations. If the reference reflector holes or the block surface are given a high polish by any chemical or mechanical means, the amplitude of the reflections obtained from these reflector holes may be altered. Polishing the holes or the block surface is not forbidden by the ASME Code. However, this possibly altered amplitude could affect the sizing of indications found during any examination. At this time, no recommendations are being made to control the surface roughness of the block or the above-mentioned reflector holes; however, if the block 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