ORNL-2106 - the Molten Salt Energy Technologies Web Site

ANP PROJECT PROGRESS REPORT
EDDY-CURRENT TESTING OF
SMALL-DIAMETER TUBING
J. W. Allen
Continued study of the application of the cyclo-
graph' to the problem of the inspection of small-
diameter tubing has revealed that, in addition to
its use as a flaw detector, the cyclograph may
also be used to gage adherence to dimensional
tolerances. Although changes in diameter and in
wall thickness are inseparable in the readout of
the instrument, the tolerance limits for both di-
mensions may be established by utilizing two
standards: (1) the minimum acceptable diameter
and wall thickness and (2) the maximum allowable
diameter and wall thickness. Dimensional checks
made by using this method, augmented with me-
chanical measurements, have been used success-
fully to determine the dimensional acceptability
oi approximately 6000 ft of ?,,-in.-OD, 0.025-in.-
'R. B. Oliver, J. W. Allen, and K. Reber, ANP Quar.
Prog. Rep. March 10, 1956. ORNL-2061, p 164.
- .- -
6 0.0275
% 0.0270
W
z
5 0.0265
-
I
k- 0.0260
J
2 0.0255
2 0.0250
3.7. NONDESTRUCTIVE TESTING STUDIES
R. B. Oliver
wal I and 0.229-in.-OD,
lnconel tubing.
0.025-in.-wall CX-900
The 200-kc cyclograph trace of a 0.229-in.-OD,
0.025-in.-wall lnconel tube that has small wallthickness
variations along its length and no perceptible
diameter variations is shown in Fig.3.7.1.
The wall thickness was plotted from Vidigage
(u I trason ic-resonance-type thickness gage) and
mechanical measurements. It may be seen that,
although there is not perfect agreement, there is
a fairly close correspondence between the two
types of checks. The disagreement is probably
due to minute amounts of eccentricity and intergranular
attack on the inside surface of the tube
having been detected by the cyclograph.
The confidence level of the interpretations of
indications from this instrument is increasing
with continued use. Because the sensing coil
observes at any one instant a section of tubing
approximately
3 /s in. long, it is not possible to
detect pin holes, except when they occur in
clusters. In general, defects can be resolved if
they have a length of b6 in. or longer and have
I
AVERAGE WALL THICKNESS DETERMINED WITH VlDlGAGE
OUTSIDE DIAMETER CONSTANT AT 0.230 in.
200-kc CYCLOGRAPH TRACE
UNCLASSIFIED
ORNL -LR-DWG 13970
0 6 12 48 24 30 36 42 48 54 60 66 72 78
LENGTH (in.)
Fig. 3.7.1. Cyclograph Record at 200 kc from a 0.229-in.-OD, 0.025-in.-Wall CX-900 lnconel Tube
Compared with Dimensional-Variation Measurements Made Mechanically and with the Vidigage.
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