T.O. 33B-1-1SECTION VIIIUT PROCESS CONTROL1.8ULTRASONICPROCESSCONTROLREQUIREMENTS.1.8.1TheUltrasonicProcessControlRequirements.In the ultrasonic inspection process like the eddy current process you must know your equipment and probeor transducer or search unit is functioning properly. The following information on process control inultrasonic testing is designed to help ensure repeatability and accuracy. All new transducers should bechecked against a reference transducer of the same dimension and frequency. Only transducers in userequire documentation on serviceability. For example, you may have 5 of the same transducers in stock butonly be using one. The one in use should be labeled to show the required gain to achieve a 100% amplitude ona specific size f law. If a transducer requires more gain than the reference transducer, you know it is then asuspect. This transducer can be used, providing you can still find the required defect called by the procedure.You should never have only one transducer for a specific application. A transducer element can separatefrom the damping material. This will cause the initial pulse to become a long ringing signal. Such a situationwill cause the transducer to fail the dead zone test. The transducer must be replaced. This type of processcontrol will help ensure quality inspections without assuming everything is working properly. Frequency ofprocess control checks on equipment should come from the operations manual on the equipment. Frequencyof transducer checks should be determined by the amount of use, which will be determined by the labsupervisor. The operator is the critical link in this process. Even if all the equipment is working properly, theinspector must follow the written procedure and use the correct standard. No deviations SHALL be madewithout proper engineering authority. In this chapter, the terms ‘‘reference standard,’’ ‘‘reference block,’’‘‘test block,’’ and ‘‘calibration standard’’ all have the same meaning as defined in the glossary. Referencestandards are used by the instrument operator. Calibration of reference standards by laboratories is notrequired. However, to insure uniform inspection sensitivity, reference standards shall be traceable to a‘‘master standard’’ in terms of discontinuity response.1.8.1.1RequiredUse.All inspections shall include the use of one or more reference standards for setting up the inspection. Inaddition, all discontinuity indications shall be compared to a reference standard by comparing the signalamplitude of the discontinuity with the signal amplitude of the reference standard. This is done either inpercent signal amplitude or by noting the difference in amplitude in decibels (dB) when the instrument isequipped with dB attenuation controls.1.8.1.2Configuration.The reference standard may be a block containing a known size f lat-bottom or side-drilled hole, machined slotor notch, or a real discontinuity of known size in the test part or a piece similar to the test part. Inspectionprocedures must be carefully reviewed for the following specific requirements:a.Flat surface reference standards used for test set-up and for evaluation of discontinuity size and metaltravel shall be fabricated and checked in accordance with ASTM standard practices. For moreinformation see ASTM E127, E128, and E1158, 2nd para. 4.2.4.5.b.Curved surface reference standards may be required when performing straight beam inspection ofcurved entry surfaces on cylindrical or irregularly shaped products. Special ultrasonic test blockscontaining specified radii of curvature and f lat-bottom holes of standard diameter shall be used. Forparts with convex radii over 4 inches, use standard f lat face blocks. Flat blocks may be used toinspect other curved surfaces when supported by test data showing correction factors, and must beacceptable to the responsible engineering activity.1-52Change 2
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