UT PROCESS CONTROL
ULTRASONIC PROCESS CONTROL REQUIREMENTS.
The Ultrasonic Process Control Requirements.
In the ultrasonic inspection process like the eddy current process you must know your equipment and probe
or transducer or search unit is functioning properly. The following information on process control in
ultrasonic testing is designed to help ensure repeatability and accuracy. All new transducers should be
checked against a reference transducer of the same dimension and frequency. Only transducers in use
require documentation on serviceability. For example, you may have 5 of the same transducers in stock but
only be using one. The one in use should be labeled to show the required gain to achieve a 100% amplitude on
a specific size f law. If a transducer requires more gain than the reference transducer, you know it is then a
suspect. 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 separate
from the damping material. This will cause the initial pulse to become a long ringing signal. Such a situation
will cause the transducer to fail the dead zone test. The transducer must be replaced. This type of process
control will help ensure quality inspections without assuming everything is working properly. Frequency of
process control checks on equipment should come from the operations manual on the equipment. Frequency
of transducer checks should be determined by the amount of use, which will be determined by the lab
supervisor. The operator is the critical link in this process. Even if all the equipment is working properly, the
inspector must follow the written procedure and use the correct standard. No deviations SHALL be made
without 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. Reference
standards are used by the instrument operator. Calibration of reference standards by laboratories is not
required. However, to insure uniform inspection sensitivity, reference standards shall be traceable to a
master standard in terms of discontinuity response.
All inspections shall include the use of one or more reference standards for setting up the inspection. In
addition, all discontinuity indications shall be compared to a reference standard by comparing the signal
amplitude of the discontinuity with the signal amplitude of the reference standard. This is done either in
percent signal amplitude or by noting the difference in amplitude in decibels (dB) when the instrument is
equipped with dB attenuation controls.
The reference standard may be a block containing a known size f lat-bottom or side-drilled hole, machined slot
or notch, or a real discontinuity of known size in the test part or a piece similar to the test part. Inspection
procedures must be carefully reviewed for the following specific requirements:
Flat surface reference standards used for test set-up and for evaluation of discontinuity size and metal
travel shall be fabricated and checked in accordance with ASTM standard practices. For more
information see ASTM E127, E128, and E1158, 2nd para. 188.8.131.52.
Curved surface reference standards may be required when performing straight beam inspection of
curved entry surfaces on cylindrical or irregularly shaped products. Special ultrasonic test blocks
containing specified radii of curvature and f lat-bottom holes of standard diameter shall be used. For
parts with convex radii over 4 inches, use standard f lat face blocks. Flat blocks may be used to
inspect other curved surfaces when supported by test data showing correction factors, and must be
acceptable to the responsible engineering activity.