is because angle beams can travel through a part by bouncing from surface to surface. Useful inspection information
can be obtained at great distances from the search unit. Angle beam inspections are particularly applicable to
Inspections around fastener holes, inspection of cylindrical components, examination of skins for cracks, and inspection
Surface Wave Method. The surface wave method uses surface (Rayleigh) waves. When inspecting thin objects
(less than one wave-length thick) with sound propagated perpendicular to the thickness direction, Lamb waves are used.
Surface Preparation. The sound entry surface is visually examined to determine if any special preparation is
required to provide a suitable condition for ultrasonic inspection. The surface finish should be 250 rhr or smoother.
Painted surfaces can normally be inspected without removing the paint if the paint is uniform and adheres tightly to the
surface. Loose paint or uneven, patched paint shall be stripped prior to ultrasonic inspection.
Inspection of Metal Plates and Sheets. Metal plates and sheets should be inspected for laminations, surface
cracks, and weldment defects. These defects are explained in the following paragraphs.
Laminations. Laminations in rolled plate or strip are formed when blowholes or internal fissures are not
welded tight during rolling, but are enlarged and flattened into sometimes quite large areas of horizontal discontinuities.
Laminations may be detected by magnetic particle testing on the cut edges of plate, but do not give indications on plate
or strip surfaces, since these discontinuities are internal and lie in a plane parallel to the surface. Ultrasonic mapping
techniques are used to define them. When inspecting parts fabricated from sheet or plate, laminations can be detected
by noting a reduction in the distance between back reflection multiples.
Surface cracks. When inspecting for surface cracks, the sound should be directed normal to the expected
plane of the discontinuity. The straight beam method is used for laminar discontinuities and the angle beam method for
Weldment defects. Several kinds of discontinuities may be formed during welding. Some are at the
surface and some are in the interior of the metal Ultrasonic testing can detect some types of weldment defects. Refer to
the applicable maintenance manual.
Inspection of Bar Stock. Bar stock should be inspected for blow holes and cracks. These are explained in the
Blow holes. A blow hole is a hole in a casting or weld caused by gas entrapped during solidification.
Cracks. Various types of cracks can be detected by ultrasonic testing methods. Refer to the applicable
maintenance manual for detection methods and interpretation.
Inspection of Tubes and Pipes. Inspection of tubes and pipes using ultrasonic testing methods should be done in
accordance with the applicable maintenance manual.
6-10. Calibration of Ultrasonic Equipment. The most important calibration is the verification of each inspection setup
through use of the applicable reference standard. It is essential that this verification be performed for each and every
inspection Attenuation measurements should be made using ASTM test block, angle beam blocks, and a surface wave
reference standard. This IS done to minimize the scattering of the sound beam. Complete procedures are found in TM