ORNL-2106 - the Molten Salt Energy Technologies Web Site

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depths greater than the background dimensional
variations in the tube,
ULTRASONIC INSPECTION OF TUBING
R. W. McClung
Approximately 6000 ft of Cx-900 lnconel tubing
has been inspected by the immersed ultrasound
method. Two sizes of tubing 3/ in. OD, 0.025 in.
'4
wall and 0.229 in. OD, 0.025 in. wall, were inspected
and the average rejection by this test
was about 2%. Each tube received a double inspection,
with the ultrasound being beamed around
the tube in two different directions to improve the
chance of detection of unfavorably oriented cracklike
defects. This double inspection of the precut
tubing reduced the inspection rate to below the
original estimate. The current inspection rate is
approximately 500 ft in an 8-hr day for lengths
up to 10 ft.
Defects 0.0015 in. deep and b6 in. long on
polished, scratch-free tubing can be detected with
PERIOD ENDING JUNE 10, 1956
'an estimated confidence of 80 to 90%. If scratches
are present they will produce signals comparable
to those from the very small defects and effectively
increase the minimum detectable defect size. If
the defect is appreciably deeper than the scratches
and if its length exceeds the maximum dimension
of the transducer, it is not difficult to differentiate
between defects and scratches. Since the ultrasonic
method is insensitive to dimensions, the
inherent dimensional variations that give trouble
in an eddy-current inspection have no effect on
ultrasonic inspection. Both the eddy-current and
the ultrasonic methods are capable of detecting
very small defects, with the eddy-current inspection
being confused by dimensional variations and
the ultrasound method being confused by scratches.
A comparison of the results of the two tests aids
in the identification of spurious signals.
A typical small defect found on the inside of
the $,-in.-OD, 0.025-in.-wall CS-900 tubing is
shown in Fig. 3.7.2. This crack is 0.0015 in.
deep (6%) and about t6 in. long.
Fig. 3.7.2. Small Defect Found by Ultrasonic Inspection on the Inner Surface of a 3/,6-in.pOD,
0.025-in.-Wall Inconel Tube. The defect is 0.0015 in. deep and gpproximately t6 in. long,
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