The search units are tted with wedges in order to transmit ultrasonic waves into the examination object at the desired angle and mode of operation. Typical couplants include glycerin, water, cellulose gel, oil, water-soluble oils, and grease. Corrosion inhibitors or wetting agents or both may be used. Couplants must be selected that are not detrimental to the product or the process.
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The search units are tted with wedges in order to transmit ultrasonic waves into the examination object at the desired angle and mode of operation.
Typical couplants include glycerin, water, cellulose gel, oil, water-soluble oils, and grease. Corrosion inhibitors or wetting agents or both may be used.
Couplants must be selected that are not detrimental to the product or the process. The couplant used in standardization should be used for the 4 examination. The standardization and examination surface temperatures should be within F 14C to avoid large attenuation and velocity differences in the wedge material.
The examination of rough surfaces generally requires a high-viscosity couplant. The temperature of the materials surface can change the couplants viscosity. As an example, in the case of oil and greases, see Table 1.
Further, intermittent contact of the search unit with the surface or auxiliary cooling of the search unit may be necessary to avoid temperature changes that affect the ultrasonic wave transmission properties of the wedge material or the characteristics of the transducer.
At higher temperatures, certain couplants based on inorganic salts or E TABLE 1 Suggested ViscositiesOil Couplants NOTE 1The table is a guide only and is not meant to exclude the use of a particular couplant that is found to work satisfactorily on a particular surface. Approximate Surface Roughness Average Ra in. In this case, the search unit face does not contact the examination surface but is spaced from it a distance of about 0. Liquid owing through the search unit lls the gap.
The owing liquid provides the coupling path and has the additional advantage of keeping the search unit temperature low if the examination surface is hot. The transducer is mounted at the required angle to a stationary axle about which rotates a liquid-lled exible tire.
A minimum amount of couplant provides ultrasonic transmission into the examination surface since the elastic tire material is in rolling contact and conforms closely to the surface.
The articial reectors may be in the form of side-drilled holes, notches, or at-bottom holes. The reference standard and the production material should have similar velocity, attenuation, curvature, and surface nish. Standardization 7. An acceptable linearity performance may be agreed upon between the examining agency and the customer. Reections from concentric cylindrical surfaces, such as provided by some IIW blocks and the AWS distance reference block, may be used to adjust sweep range and delay.
However, if the part has suitable geometry, the part provides a more reliable standardization. Where the inspection 5 zone includes the full volume between parallel surfaces, it is recommended that at least one Vee path be marked on the screen when examining in one direction or at least one-half Vee path when examining from surface to surface in two directions.
Surface notches can also accomplish this end under some circumstances. The reector indication can be used to adjust the gain control in the desired level for detecting the minimum size reector. For quantitative evaluation, distance amplitude correction may be performed electronically, by drawing a distance amplitude correction DAC curve on the screen, or by the use of charts and curves showing the relationship of amplitude and distance for a particular search unit and material.
Move the reector through the beam to 18, 38, 58, 78, and 98 of the Vee path. Adjust delay to place indication 1 at sweep division 1. Adjust range to place indication 9 at sweep division 9. Since these controls interact, repeat the delay and range adjustments until indications 1 and 9 are placed at sweep divisions 1 and 9.
At this gain, mark the maximum amplitudes on the screen from the reector at 1, 3, 5, 7, and 9. Connect these points for the distance amplitude correction DAC curve or compensate electronically if equivalency can be demonstrated.
Corner reections from the hole to the surface may be observed at about 4 and 8 divisions on the sweep. These indications will not be used in the distance amplitude correction DAC curve. Measure position of the reector on the surface from the front of the search unit or the beam centerline projection on the side of the wedge to the surface projection of the hole.
Since the depth to the hole is known, the standardization provides means for estimating the position, depth, and relative response of an unknown reector. The sweep time trace on screen should be standardized for distance from the search unit to the reference reector.
The ordering data shall state the maximum allowable depth discontinuity that can then be used as the reference reector. The examination frequency f should approximately equal the Rayleigh wave velocity VR in the material divided by four times the E FIG.
This frequency will produce a beam with sufficient depth of penetration to give higher amplitudes from reectors with greater depths. The desired reference discontinuity may be either a thickness differential or a discontinuity reector. The Lamb wave travels at its group velocity, which is different for each mode and is different from the phase velocity.
The sweep time trace on the screen should be standardized for distance from the search unit to the reference reector. A suitable Lamb-wave type and mode shall be chosen in order to obtain a reference indication from the reference reector.
Procedure 8. Angle-beam shear waves between 1 and 40 generally should not be used because a higher amplitude angle-beam longitudinal wave may coexist and confuse the examination. In the 1 to 40 beam angle range, angle-beam longitudinal waves will give higher amplitudes than the coexisting lower angle shear 6 7. The phase velocities of the various modes of the asymmetrical and symmetrical waves depend upon the frequency of the ultrasonic wave and the thickness of the material.
Therefore, it is necessary that the E waves. Three subgroups may be identied within this group: single transducer; parallel beam, dual transducer; and crossed beam, dual transducer search units. Scan the material so that the beam is perpendicular to the major face of the aw in areas where the aw may be present. In the dual-transducer search unit, the transmitter transducer and wedge are separated from the receiver transducer and wedge by material that reduces crosstalk.
The beam directions of the transmitter and receiver will be essentially parallel. Except for operation of the instru- FIG. The range of depth that can be examined with these search units depends on the transducer size and beam angle.
Except for improved near-surface resolution, possibly limited depth range, the extra care required for depth standardization, and operation of the instrument in the through transmission mode, application of these search units is similar to straight-beam examination as described in Practice E The principles involved in this technique are illustrated in Fig.
The side of the drilled hole provides a cylindrical reector similar to a slag inclusion. Other aws and aw orientations are possible. It is imperative, therefore, that a study be made of the anticipated aws to determine the most likely orientation so that the ultrasonic beam may be 7 E directed to produce reections.
Often a number of beam directions or a rotational aiming of the beam will be needed if aw orientation can be random. Inclusions of voids that are rough, irregular, or spherical provide multidirectional reections and require less aiming of the beam. Cracks due to stress, incomplete fusion welds, etc. Materials that have been rolled, forged, or otherwise formed in the solid state may exhibit cracks at right angles to the stress direction of ow or laminations in a plane parallel to the examination surface.
Unless otherwise stated, identify the peak indications only. Examination Data Record 9. Interpretation of Results Geometric indications should be identied. Indications that are not identied as geometric and that exceed the rejection level shall be rejected unless it is agreed by the customer or determined from the part drawing that the defects will not remain in the nished part.
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ASTM E587 PDF
Document Center Inc. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Significance and Use An electrical pulse is applied to a piezoelectric transducer which converts electrical to mechanical energy. In the angle-beam search unit, the piezoelectric element is generally a thickness expander which creates compressions and rarefactions. This longitudinal compressional wave travels through a wedge generally a plastic. The angle between transducer face and the examination face of the wedge is equal to the angle between the normal perpendicular to the examination surface and the incident beam.
More E In the angle-beam search unit, the piezoelectric element is generally a thickness expander which creates compressions and rarefactions. This longitudinal compressional wave travels through a wedge generally a plastic. The angle between transducer face and the examination face of the wedge is equal to the angle between the normal perpendicular to the examination surface and the incident beam.