Page 108 - SSAB Welding Handbook Edition 2

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18.0 Non destructive evaluations Welding handbook

During conventional inspection, ultrasonic waves are
transmitted to the inspection area by a probe. The
©SSAB
reflected echo of the ultrasonic waves can be identified
by the same unit, which is illustrated in fig. 18.6, or
by a separate probe.

s

20° D

Search angle (45°)
Fig. 18.6: Ultrasonic testing of a joint without discontinuities.

The response from the echo is converted to electrical
signals that can then be displayed with an oscilloscope.
Ultrasonic testing compares echoes from a section
with no discontinuities to deviating echoes from a
section with a discontinuity. Based on the outcome
of the echo, the shape, size and position of a detected
discontinuity can be determined.

Detection of a discontinuity is illustrated in
fig. 18.7 and fig. 18.8, where a discontinuity echo
is illustrated in the latter figure. Discontinuity echo

Fig. 18.8: Detection of a discontinuity with ultrasonic testing. The
discontinuity echo is displayed on the screen of the oscilloscope.

The inspection of the joint starts with cleaning
the area around the joint to remove any foreign
20° D substances and contaminants. This also includes

removal of any outer irregularities such as spatter
and slag that are present on the surface.

Fig. 18.7: Ultrasonic testing of a joint where a crack that is detected.
A couplant is then applied between the probe and
the inspection area. Its function is to support the
transmission of the ultrasonic waves between the
probe/probes and the area to be inspected. Examples
of couplants are oil, glycerin, water and silicon.

108 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.