N. Set the back wall signal to 100% of full screen height.
O. Add 4 dB. During the inspection, if there are cracks the crack signals will be above 40% of full screen
height.
5. Inspection Procedure
NOTE: Each fuse pin must be examined from both the inboard and outboard ends of the fuse pin. Each
scan will examine the bottleneck area on the far side of the fuse pin for cracks. This is done so that
the internal reflection signals will not be in the inspection area and will not be incorrectly identified as
cracks. See Paragraph 4.
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 at one end of the fuse pin. See Figure 6.
D. Put the transducer guide on the fuse pin. Make sure the signal from the back surface is at the correct
screen location identified in Table 1 for the specific fuse pin that is examined. If you do not get a back
surface signal, move the transducer to a different position and try again.
E. Make a scan of the fuse pin. As you make a scan, monitor the ultrasonic signals which occur between
42% and 65% of full screen width. Also monitor the first signal from the back surface to make sure the
transducer fully touches the fuse pin.
NOTE: A loss of 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 ultrasonic signals that are out of the area of interest (between 20%
and 35% of full screen width) but stay on the screen during the full inspection of the fuse pin. These
signals can occur because of internal reflections of the ultrasonic sound waves (see Figure 5, Detail
I). Cracks which are located on the near end of the pin will show on the screen in the internal
reflection area (outside the area of interest), or close to the initial pulse. These cracks will be found
when the inspection is done from the opposite end of the fuse pin.
(2) A crack will usually cause the ultrasonic signal from the back surface to decrease below 100%
full screen height.
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 in the inspection range that is 40% or more of
full screen height. See Note (1) at the start of Paragraph 6. and then 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.
747
NONDESTRUCTIVE TEST MANUAL
PART 4 54-30-07
Page 3
Nov 15/2015D6-7170
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
ALL
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