T9074-AS-GIB-010/271 Rev 1
B.5 PREREQUISITES.
B.5.1 Inspection Area. The area requiring sizing and characterization inspection shall be established from prior ultrasonic detection inspections. The original inspection report shall be reviewed and the same ultrasonic detection procedure should be utilized to confirm the presence of the discontinuity prior to ultrasonic characterization or sizing inspection. The same or similar equipment shall be used for the verification inspection. Ultrasonic sizing inspection should only be applied after the ultrasonic characterization evaluation has been completed. Ultrasonic characterization is performed to determine if reported discontinuities are volumetric or planar in nature, and to disposition the type of discontinuity (for example, thinning, corrosion, lamination, inclusion, etc.). B.5.2 Recommended Practice. The nature of the discontinuity requires the use of multiple techniques to accurately characterize and size. No one technique is best for sizing all discontinuities. Whenever possible, the discontinuity shall be evaluated from all sides and verification of the discontinuity characterization and through wall dimension shall be confirmed using more than one technique. B.5.3 Surface Preparation. The inspection surface shall be free of paint, grease, dirt, or any other material that might interfere with scanning. Surfaces to be inspected shall have a finish of not greater than 250 Ra microinches. Surface waviness shall not interfere with search unit contact. Weld crowns may need to be ground or removed to permit transducer access for discontinuity characterization and sizing. B.5.4 Scanning. The inspector shall select areas along the length of the discontinuity to be sized in order to obtain a profile and to aid in identifying the deepest point. B.5.5 Scanning Considerations. An inspection site shall be considered accessible for longitudinal and half skip shear wave inspection if obtaining access to the site: a. Does not require hot work (welding) or docking of the ship. b. Limits the removal of wire ways, piping, ducting, lockers, sheet metal work, foundations, etc. c. Will not cause a major delay to ships schedule. d. Does not prove hazardous to personnel.
B.6 DISCONTINUITY CHARACTERIZATION.
B.6.1 Characterization. Prior to performing ultrasonic sizing, the discontinuity must be characterized as either planar or volumetric. Thinning, corrosion, or laminations may also be encountered and should be clearly characterized. The following techniques are used for characterization of discontinuities and shall be used on each discontinuity that is evaluated as configuration allows. B.6.2 Straight Beam Evaluation. When possible, the inspector shall scan the discontinuity with a dual element straight beam transducer. A planar discontinuity may exhibit little or no amplitude while a volumetric discontinuity should be readily detected. B.6.3 Shear Wave Evaluation. The inspector shall perform shear wave examination of the area of interest, inspecting it from all directions. A planar discontinuity will exhibit a large change in amplitude with changing beam angle. A volumetric discontinuity will exhibit more consistent signal amplitude, regardless of beam angle. B.6.4 Echo Dynamics. The inspector shall evaluate the general nature and echo dynamic characteristics of the signal as the transducer is moved toward and away from the peaked location. A planar discontinuity will show a smooth echo dynamic response, similar to the response from a side-drilled hole. A volumetric discontinuity will exhibit multiple peaks at several depths along the length of the discontinuity.
B-3
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