5. Inspection Procedure
NOTE: Each fuse pin must be examined from the inboard and outboard ends of the pin. See Figure 1.
A. Prepare for the inspection as specified in Paragraph 3.
B. Do the instrument calibration as specified in Paragraph 4.
C. Put couplant on the inspection area of the fuse pin. See Figure 6.
D. Put the transducer guide on the fuse pin and make sure the signal from the back surface agrees with
Table 2 and Figure 6. If you do not get a back surface signal, move the transducer to a different
position and try again.
NOTE: If you do not get a back surface signal, check to make sure there is good transducer contact. If
the transducer has good contact, add more gain to get a signal from the back surface that is
approximately 100% full screen height.
E. Make a scan of the fuse pin. As you make a scan, monitor the ultrasonic signals which occur between
10% and 30% full screen width. Also monitor the first signal from the back surface to make sure you
keep full transducer contact.
NOTE: A loss of the back surface signal can be caused by a cracked fuse pin.
F. Do Paragraph 5.C. thru Paragraph 5.E. again on the opposite end of the fuse pin.
G. Refer to Paragraph 6. to make an analysis of the ultrasonic signals that occurred during this inspection.
6. Inspection Results
NOTE: (1) Some fuse pins can have an ultrasonic signal that is out of the area of interest but stays on the
screen during the full inspection of the fuse pin. This signal can occur because of mode conversion
of the ultrasonic sound waves. If the signal is caused by mode conversion, the signal will be small in
amplitude while the ultrasonic signal from the back surface will be large. A crack will usually cause
the ultrasonic signal from the back surface to decrease below 100% full screen height and a signal
from the crack will occur at a lesser screen range.
NOTE: (2) It is possible that an off angle crack will not give a return echo, but will cause a loss of signal
from the back surface.
A. A fuse pin that does not have a crack indication is acceptable.
B. Do more analysis on a fuse pin with an ultrasonic signal that is 40% or more of full screen height, and
is between 10% and 30% full screen width. Refer to Table 2 for the expected crack locations. Do more
analysis as follows:
(1) Make sure that the signal is not caused by too much couplant. Clean the inspection area of all
couplant and then put only a small quantity of couplant on the inspection area. Do the inspection
one more time. If the ultrasonic signal was caused by too much couplant, it will be gone. If the
ultrasonic signal does not go away, continue to Paragraph 6.B.(2).
(2) It is possible that a surface condition has caused the signal. Look at the inner diameter of the fuse
pin at the approximate location where the ultrasonic indication occurs. Try to finger-dampen the
ultrasonic signal. Put a small quantity of couplant on your finger and rub the inner diameter of the
fuse pin at the location where the ultrasonic signal occurred. The signal will move up and down a
large amount if a surface condition has caused the ultrasonic signal. If the ultrasonic signal can
not be dampened, reject the fuse pin.
C. Make a record of all ultrasonic signals that are less than 40% full screen height and between 10% and
30% full screen width so you can refer to these records when you do this inspection again.
747
NONDESTRUCTIVE TEST MANUAL
PART 4 54-30-08
Page 3
Nov 15/2015D6-7170
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
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