Metals Testing Company
C-Scan Primer
The following is a quick introduction to ultrasonic (UT) C-Scan terminology and technology.
C-Scan: A view within a part from the perspective of the ultrasonic transducer’s scanning surface (a.k.a.,
top or plan view). For example, if scanning a pipe from its outer diameter, the C-Scan is the view looking
into the part from OD to ID.
B-Scan: A cross-section view within a part perpendicular to the scanning surface (a.k.a., side view). The BScan slice is in the same direction as the scanning path of the transducer.
B’-Scan: An additional cross-section view within a part perpendicular to the scanning surface and also
perpendicular to the B-Scan (a.k.a., end view, B-Prime Scan view). The type of system we own can display
either a B-Scan or B’-scan, not both at the same time on the same image (other ways exist to show both).
A-Scan: The raw data, ultrasonic signal captured by the system. Its location is at the pixel at the cursor
cross hair in the C-Scan. It is also the vertical cursor shown in the B-Scan and B’-Scan views. The overall
digitized and saved UT signal is each entire A-Scan (green & red areas on A-Scan signal). The red portion
of the signal is the C-Gate. The C-Gate represents the volume within the material that the C-Scan
interrogates. The A-Scan signal can be as many as 4096 data points. Once collected, a C-Gate can be
changed to focus on a different area of interest within the part without having to physically rescan it.
The following is an example of thickness and simulated flaw size changes using C-Scan imaging. Note that
a photograph of the actual part scanned is not available, but a similar sample is shown below. Also note that
the data is from a composite material, not steel. Additional information about the composite image and
application can be found in MTC UT Capabilities literature entitled “Composite Inspection”.
Top/Scanning Surface
Backwall
thickness
changes
Cross Sectional View
Example of a step wedge calibration standard laying on its side
An images of a similar step wedge made out of composite materials is shown on the following page.
Voice: 860-289-8225
Fax: 860-289-5970
80 Kimberly Drive
South Windsor, CT 06074
e-mail: mtc62@aol.com
website: www.mtc62.com
Metals Testing Company
C-Scan
(top view)
Holes drilled from
backside
B-Scan
(side view)
Backwall steps
A-Scan
UT Signal
Front surface interface noise
The above images provide positional location (XY), depth, relative size, and magnitude of indications in
the inspected sample.
Note that the A-Scan is of the smallest diameter flat bottom hole drilled to the mid-wall of the third thickest
area of the sample. Note that the colors in the C-Scan view represent material thickness. Colors in the BScan represent UT signal amplitude. Other views and scales are also available for both the C & B-Scans.
The red signal in the A-Scan is the window in time that the C-Scan pixel’s value originates from. Note that
the front surface interface noise ring down is captured in the recorded A-Scan signal but is not masking
signals of interest behind it. This is the result of setting the C-Gate (red line) to begin after the front
interface signal.
This is just a quick overview of how UT signals can be more readily recognized when part of a bigger
image. If you have any questions in this subject, please don’t hesitate to contact us.
Voice: 860-289-8225
Fax: 860-289-5970
80 Kimberly Drive
South Windsor, CT 06074
e-mail: mtc62@aol.com
website: www.mtc62.com