ASME V-2008 pdf download

ASME V-2008 pdf download.NONDESTRUCTIVE EXAMINATION.
B-463.2 Calibration From Unclad Surface. When the examination is performed from the outside surface, cali- brate on the 1 ⁄ 8 in. (3 mm) diameter side-drilled holes to provide the shape of the DAC from 1 ⁄ 2 in. (13 mm) to 1 ⁄ 4 T depth.Setthegaintomaketheindicationfrom 1 ⁄ 8 in.(3mm) diameter side-drilled hole at 1 ⁄ 4 T depth the same height as the indication from the 1 ⁄ 4 T depth hole as determined in B-462.1 or B-462.2 above. Without changing the gain, determinethescreenheightoftheothernearsurfaceindica- tions fromtheremaining 1 ⁄ 8 in. (3mm) diameter side-drilled holes from 1 ⁄ 2 in. (13mm) deep to the 1 ⁄ 8 in. (3 mm) diameter side-drilled hole just short of the 1 ⁄ 4 T depth. Connect the indication peaks to complete the near surface DAC curve. Return the gain setting to that determined in B-462.1 or B-462.2. B-463.3 Calibration From Clad Surface. When the examination is performed from the inside surface, calibrate on the 1 ⁄ 8 in. (3 mm) diameter side-drilled holes to provide the shape of the DAC and the gain setting, as per B-463.2 above. B-464 Position Calibration (See Fig. B-464) The following measurements may be made with a ruler, scale, or marked on an indexing strip. 3 B-464.1 1 ⁄ 4 T SDH Indication. Position the search unit for maximum response from the 1 ⁄ 4 T SDH. Place one end of the indexing strip against the front of the search unit, the other end extending in the direction of the beam.
B-464.2 1 ⁄ 2 T and 3 ⁄ 4 T SDH Indications. Position the search unit for maximum indications from the 1 ⁄ 2 T and 3 ⁄ 4 T SDHs. Keep the same end of the indexing strip against the front of the search unit. Mark the numbers 4 and 6 on the indexing strip at the scribe line, which are directly above the SDHs. B-464.3 5 ⁄ 4 T SDH Indication. If possible, position the search unit so that the beam bounces from the opposite surfacetothe 3 ⁄ 4 TSDH.Markthenumber10ontheindexing strip at the scribe line, which is directly above the SDH. B-464.4 Notch Indication. Position the search unit for the maximum opposite surface notch indication. Mark the number 8 on the indexing strip at the scribe line, which is directly above the notch. B-464.5 Index Numbers.
This technique provides good resolution in the axial direction by using broadband search units. These search units transmit a very short pulse, and therefore the axial resolution is improved. The maximum bandwidth may be 20 MHz without using filtering, and up to 8 MHz using an integrated filter. Analysis measurements, in general, are performed to obtain information on size, volume, location, and configu- ration of detected flaws. The results of the holography- measurements per scan line show a two-dimensional image of the flaw by color-coded display. The size of flaws can be determined by using the 6 dB drop in the color code. More information on the flaw dimensions is obtained by scans in different directions (ie, parallel, perpendicular) at different angles of incidence. To decide if the faw is a crack or a volumetric flaw, the crack tip technique offers one criterion and comparison of two measurements from different directions of incidence offers another. Measure- ment results obtained by imaging techniques always require specific interpretation. Small variations in material thickness, sound velocity, or refracted beam angle may influence the reconstruction results. The holography pro- cessing calculations also assume that the velocity is accu- rately known and constant throughout the material. Flaw sizing is normally performed by measuring the vertical extent (in the case of cracks) or the cross-sectional distance (in the case of volumetric/planar flaws) at the 6 dB levels once the flaw has been isolated and the image normalized. Tandem sizing and analysis uses techniques similar to pulse echo but provides images that are easier to interpret since specular reflection is used for defects oriented perpendicular to the surface. For cracks and planar defects, the result should be verified using crack-tip-diffrac- tion signals from the upper and lower ends of the flaw, since the phased array approach with tomographic recon- struction is most sensitive to flaw tip indications and is able to give a clear reconstruction image of these refraction phenomena. As with other techniques, the phased array process assumes isotropic and homogeneous material whose acoustic velocity is constant and accurately known.