T9074-AS-GIB-010/271 Rev 1
6.8.2 Transducers. Transducers shall not be greater than 1-inch square or 1 ⅛ -inch diameter, and shall operate within a range of 2.25 to 10.0 MHz. 6.8.3 Calibration of Test Equipment. Calibration of ultrasonic test equipment shall be performed on a calibration block to establish adequate sensitivity for testing. The calibration standard shall meet the surface finish requirements of 6.3.2. The calibration standard shall be prepared by weld deposited cladding, pads, or buttering onto a block of the same S-number (or equivalent as defined in S9074-AR-GIB-010/278) base material as the production part. The weld deposited metal used must be of the same A-number as that on the production part to be examined and may be deposited by any approved welding process. In addition, the following requirements in (a) through (g) shall be met (the S-numbers and A-numbers for base metal and weld metal are defined in S9074-AR-GIB-010/278): a. The microinch surface finish of the calibration standard shall be equal to or greater than the production part to be inspected. b. The calibration standard base material shall be equal in thickness to the production part base material except that, for thicknesses exceeding 1 inch, the calibration standard base material may be 1 inch or greater. For welding large flat or essentially flat surfaces, a 6-inch square shall be the minimum acceptable size of the calibration block. c. The weld metal thickness of the calibration standard shall be within plus or minus 25 percent of that on the production part. d. The transducer contact area of the production part shall be equal to or greater than the transducer contact area on the calibration standard. e. For convex production surfaces, the calibration standard shall be convex with a radius of curvature equal to or less than the production surface to be examined. f. For concave production surfaces, the calibration standard may be flat or concave with a radius of curvature equal to or greater than the production surface to be examined. g. An area of the block approximately 2 inches square shall have the backing material removed, leaving only the cladding. An ultrasonic thickness measurement at 2.25 MHz shall be established in this area, representing unbond. The thickness pattern obtained in the area of integral cladding and base material shall represent good bond and the first clearly visible reflection from the opposite side of the block shall not be greater than full screen amplitude. Calibration shall be obtained with the search unit moving across the surface at approximately the same speed as that to be used during the inspection. 6.8.4 Scanning. Scanning shall be performed manually or automatically by moving the search unit in a directed path or by moving the material in a directed path with the search unit stationary. Scanning shall be performed at a uniform rate of speed determined during calibration, so that any indication relative to the quality of the material shall be detected. 6.8.4.1 Continuous Scanning. Unless otherwise specified in the appropriate specifications, the continuous scanning procedure shall be followed. All testing shall be performed with the search unit in contact with the clad surface. Sound transmission into the base material shall be confirmed by observing the composite thickness pattern as obtained from the good bond area of the calibration standard. When the back reflection is lost due to nonparallel surfaces of the base materials, transmission shall be confirmed by the test specified in 6.8.4.3. 6.8.4.2 Intermittent Scanning. Scanning shall be performed along special paths or on grid lines. The distance between paths or lines shall be as specified in the appropriate specification when the method is required. 6.8.4.3 Calibration for Ultrasonic Testing of Nonparallel Surfaces. Test equipment shall be calibrated with the same calibration standard as specified in 6.8.3. The thickness pattern shall be observed by scanning over the clad surface where the backing material has been removed, and the equipment shall be set to demonstrate a full screen back reflection. Using these settings, the operator shall scan over the composite thickness of the cladding and the backing material and note the normal back reflection from the good bond.
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