L. Examine all noise signals to make sure the signal-to-noise ratio is larger than 3:1. If the signal-to-noise
ratio is less than 3:1, try a different transducer or a higher frequency transducer.
NOTE: Make sure the initial pulse is not greater than 8% of full screen width. If necessary, adjust the
instrument controls or use a different transducer.
5. Inspection Procedure
NOTE: Each fuse pin must be examined from the inboard and outboard ends of the pin. Make sure the
correct reference standard step is used for each fuse pin to be examined. 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 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 is at the
correct screen location identified in Table 1. If you do not bet 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
the initial pulse signal and 40% 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: 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.
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. See
the Note at the start of Paragraph 6. and then do more analysis in the monitored area 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 54-30-05
Page 3
Nov 15/2015D6-7170
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
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