The Advanced Flaw Sizing Technique Handbook outlines the requirements for contact methods using refracted longitudinal and shear wave techniques for ferritic and austenitic materials. Other techniques may be applicable when an appropriate calibration sizing block is utilized. Special longitudinal and/or shear wave search units and special ultrasonic sizing calibration blocks are used for the sizing examinations. These techniques are applicable to both manual and automated examinations.
ASME Code Section V, Articles 4 and 5 requires flaw sizing using decibel (dB) drop sizing methods. It has been demonstrated that when the flaw is less than the beam spread, the dB drop sizing method tends to size the search unit beam spread in lieu of the actual flaw size or depth. Thus, conservatively over sizing, or maybe under sizing, the actual depth of the flaw. The sizing techniques outlined herein use Time-of-Flight (TOF) or Sound Path (SP) measurements to more accurately size the flaw depth.
Flaw characterization and sizing methods such as ID Creeping Waves, Tip Diffraction, Bi-Modal, and Refracted Longitudinal Waves have demonstrated a higher degree of accuracy for sizing the depth of planar flaws in pipe, plate and vessel components, in lieu of the Amplitude Comparison or dB Drop Techniques.
The advanced ultrasonic sizing techniques used in the Flaw Sizing Handbook have been demonstrated on actual crack specimens and are approved by an ASNT UT Level III and UT Sizing Qualified Examiner.
As with any flaw sizing technique or procedure, the author highly recommends that an approved sizing procedure shall be qualified using actual cracked specimens. An appropriate sizing performance practical demonstration should be performed in accordance with paragraph 4.3 of the UT Sizing Procedure in Chapter 6 page 34 in order to qualify the equipment, technique, and personnel.
An ultrasonic sizing procedure should be developed and qualified for equipment, technique, and sizing examination personnel. At least 10 flawed specimens should be used in the performance demonstration. A Root Mean Square (RMS) evaluation should be used to demonstrate adequate sizing performance. This is given by the formula:
| RMS = |  |
(T - U)2
| ------------
| N
| |
U = Ultrasonic flaw depth estimate
N = Number of test specimens or flaws sized
Acceptable flaw sizing performance demonstration is achieved when the RMS is 12.5% or less. This is comparable to the Appendix VIII criteria proposed in ASME Code Section XI. Accordingly, it was demonstrated that at an RMS of 15% or less, acceptable sizing performance is achieved comparable to the current EPRI NDE Center Intergranular Stress Corrosion Cracking (IGSCC), Sizing Program.
The advanced ultrasonic sizing techniques described in this handbook have been developed in accordance with recommended guidelines of the EPRI NDE Center Ultrasonic Planar Flaw Sizing of IGSCC. Variations or modifications of the techniques have been incorporated to improve accuracy of flaw depth sizing of stress corrosion, thermal fatigue and mechanical fatigue cracks.
The acronyms used in the industry and in this handbook to identify the applicable sizing technique are used only as a reference. Some techniques are identified by two sets of acronyms. However, the appropriate method or technique is best identified by the wave physics terminology and the associated calibration method.
One of the most important aspects of this book for the ultrasonic inspector is to apply the sizing techniques together with detection techniques when examining coarse grain materials. The Refracted Longitudinal wave techniques allow the ultrasonic beam to penetrate coarse grain materials such as weld metal, cast grain structure, and even weldments in nickel based alloys such as incalloy and hastelloy.