ASTM-E114:2020 pdf free download – Standard Practice for Ultrasonic Pulse-Echo Straight-Beam Contact Testing.
7.6 For bond/unhond (fusion/lack of fusion) examinations, a reference standard should he used similar to the production item being examined containing areas representing both bonded (fused) and unbonded (lack of fusion) conditions, if geometry and material permit.
7.7 Standardization with respect to reference standards should be penodically checked to ensure that the ultrasonic system standardization is not changing. As a minimum, the standardization shall be checked each time there is a change of operators, when search units are changed. when new batteries are installed, when equipment operating from one power source is changed to another power source, or when improper operation is suspected.
8. Procedure
8.1 When ultrasonic examinations are performed for the detection or sizing of discontinuities, or both, reflectors not perpendicular to the ultrasonic beam may he detected at reduced amplitudes. These indications exhibit a distorted envelope depending upon the reflector area, whether it is curved or planar, whether it is smooth or rough. or perhaps with reflecting facets. Reflector characteristics may also cause rapid shifts in apparent depth as the search unit approaches or moves away from the low amplitude indication. Another effect of these reflectors is the loss of back reflection which occurs when the discontinuity lies directly between the search unit and the back surface. Reflectors detectable due to any of the foregoing phenomena cannot be sized solely on signal amplitude but require special corrections for search unit and flaw characteristics.
8.2 Exa,niizaiion Su,face—Surfaces shall be uniform and free of loose scale and paint. discontinuities such as pits or gouges. weld spatter, dirt, or other foreign matter which affect examination results. Tightly adhering paint, scale, or coatings do not necessarily need to be removed for examining if they present uniform attenuation characteristics. The examination surface must be adequate to permit ultrasonic examination at the sensitivity specified. If needed, surfaces may be ground, sanded, wire brushed, scraped. or otherwise prepared for examining purposes. Curved surfaces, either concave or convex, may be examined: however, the standardization system should compensate for the effective change in search unit transmitting area between the reference standard and production item. If practical, the reference standard should have the same geometry as the item being examined.
8.3 Search Unit—Select a suitable search unit size and frequency after consideration of the acoustic characteristics of material to be examined, the geOmetry of the production item, and the minimum size and type of discontinuity to be detected. The higher the frequency selected, the higher the resolving capability accompanied with a decrease in penetrating power; conversely, the lower the frequency used, the greater the penetrating power with decreasing resolving capability. Factors limiting the use of higher frequencies are the equipment and the material properties. The limiting use of lower frequencies is the loss in sensitivity level for the examination and increasing beam spread. Various types of straight-beam search units are available offering advantages for specific applications. The above statements should be considered when choosing the search unit size, type. and frequency. When delay materials are used in the search unit, the standardization and examination surface temperatures should be within 25 °F (14 °C) to avoid large attenuation and velocity differences.