Significance and Use
The practices referenced in this document are applicable to measuring the height of planar flaws open to the surface that originate on the far-surface or near-surface of the component. These practices are applicable to through-wall sizing of mechanical or thermal fatigue flaws, stress corrosion flaws, or any other surface-connected planar flaws.
The techniques outlined describe proven ultrasonic flaw sizing practices and their associated limitations, using refracted longitudinal wave and shear wave techniques as applied to ferritic or austenitic components. Other materials may be examined using this guide with appropriate standardization reference blocks. The practices described are applicable to both manual and automated examinations.
The techniques recommended in this standard guide use Time of Flight (TOF) or Delta Time of Flight (ΔTOF) methods to accurately measure the flaw size. This guide does not include the use of signal amplitude methods to determine flaw size.
Generally, with these sizing methods the volume of material (or component thickness) to be sized is divided into thirds; the inner 1/3, the middle 1/3 and the outer 1/3. Using the far-surface Creeping Wave Method the user can qualitatively segregate the flaw into the approximate 1/3 zone.
The sizing methods are used in 1/3 zones to quantitatively size the crack, that is, Tip-diffraction for the inner 1/3, Bi-Modal method for the middle 1/3, and the Focused Longitudinal Wave or Focused Shear Wave Methods for the outer 1/3. These 1/3 zones are generally applicable to most sizing applications, however, the various sizing methods have applications outside these 1/3 zones provided a proper reference block and technique is demonstrated.
Scope
1.1 This guide provides tutorial information and a description of the principles and ultrasonic examination techniques for measuring the height of planar flaws which are open to the surface. The practices and technology described in this standard guide are intended as a reference to be used when selecting a specific ultrasonic flaw sizing technique as well as establishing a means for instrument standardization.
1.2 This standard guide does not provide or suggest accuracy or tolerances of the techniques described. Parameters such as search units, examination surface conditions, material composition, etc. can all have a bearing on the accuracy of results. It is recommended that users assess accuracy and tolerances applicable for each application.
1.3 This document does not purport to provide instruction to measure flaw length.
1.4 This standard guide does not provide, suggest, or specify acceptance standards. After flaw-sizing evaluation has been made, the results should be applied to an appropriate code or standard that specifies acceptance criteria.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
