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CHAPTER EIGHT
THRU PAINT MEASUREMENT TECHNIQUE
8.1 Introduction to Thru Paint Measurement
The principle behind thru paint measurement is by measuring the time between two
backwall echoes returning from the test material. Since both of these backwall
echoes travel the same path through the paint or coating, the thickness of the coating
is subtracted out of the measurement so that only the actual material thickness can
be measured. This feature saves the user a great deal of time scraping and
removing the coating from tanks and pipes during the inspection process.
The
DFX-7
also has a special echo-echo verify option, or triple echo mode. This
measurement mode is identical to the echo-echo mode described above, with an
additional third echo measurement performed to verify the measurement between the
first 2 echoes. By doing this, the
DFX-7
can confirm that a peak jump has not
occurred, and the measurement made is stable and correct. This mode is only
suitable for thin materials and coatings, as the ability to achieve 3 reflections is not
always possible.
The primary purpose of thru paint measurement is to determine actual or overall
material thickness by eliminating the coating thickness. Thru paint mode cannot be
used for flaw or pit detection. Therefore, inspectors may need to use echo-echo thru
paint mode in conjunction with the standard pulse-echo flaw detection mode for some
applications. The combination of using both modes is ideal for the advanced
inspectors needs.
8.2 Using Thru Paint Mode
The first thing to note in this section, is that by selecting the transducer type from the
list of probes stored in the
DFX-7
, a basic echo-echo thru paint configuration is
recalled from memory. Each of the transducers in the list contains pre-configured
echo-echo settings. However, fine adjustments may be necessary in order to be
suitable for your specific applications. These configurations are general setups only.
Once the transducer has been selected, or auto detected, and the appropriate
calibration procedure completed, the
DFX-7
can toggle between
pulse-echo
(flaw &
pits), and
echo-echo
(thru-paint) modes by simply pressing the
MULTI MODE
key
located on the keypad. The standard transducer that will be used for common steel
applications is a ¼” 5MHz high damped transducer
(1/4IN – 5.0MHZ HD)
. However,
any of the transducers with the
HD
label have been optimized for echo-echo thru
paint applications. Any of the auto recognition coating transducers are also high
damped transducers, and will work in echo-echo mode as well.
Note: When a transducer is selected for use, all of the measurement modes
available for use with this transducer can easily be determined by pressing the multi-
