Page 264 - CITS - Welder - Trade Theory

WELDER - CITS

The Principle : In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over
the object being inspected. The transducer is typically separated from the test object by a couplant (such as oil)
or by water, as in immersion testing.

There are two methods of receiving the ultrasound waveform, reflection and attenuation. In reflection (or pulse-
echo) mode, the transducer performs both the sending and the receiving of the pulsed waves as the “sound” is
reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object
or from an imperfection within the object. The diagnostic machine displays these results in the form of a signal
with an amplitude representing the intensity of the reflection and the distance, representing the arrival time of the
reflection. In attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface,
and a separate receiver detects the amount that has reached it on another surface after traveling through the
medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount
of sound transmitted, thus revealing their presence.
Advantages:
• High penetrating power, which allows the detection of flaws deep in the part.

• High sensitivity, permitting the detection of extremely small flaws.
• Only one surface need be accessible.
• Greater accuracy than other non-destructive methods in determining the depth of internal flaws and the
thickness of parts with parallel surfaces.
• Some capability of estimating the size, orientation, shape and nature of defects.
• Non-hazardous to operations or to nearby personnel and has no effect on equipment and materials in the
vicinity.
• Capable of portable or highly automated operation.
Disadvantages:
• Manual operation requires careful attention by experienced technicians
• Extensive technical knowledge is required for the development of inspection procedures.

• Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
• Surface must be prepared by cleaning and removing loose scale, paint, etc, although paint that is properly
bonded to a surface usually need not be removed.

• Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts
being inspected unless a non-contact technique is used. Non-contact techniques inclined Laser and Electro
Magnetic Acoustic Transducers (UMAT)
• Inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors,
• inspected items must be water resistant, when using water based couplants that do not contain rust inhibitors,

251

CITS : C G & M - Welder - Lesson 83 - 97