TM 1-1520-264-23
Change 1 2-38.7/2-38.8 blank)
“S” SCAN
SUPPLEMENTAL SCAN FOR THE STRAP PACK BOLT INSPECTION
Description. An additional scan is required to detect cracks initiating at more severe
angles from the inner wall of the strap pack bolt.
(1)
SET UP
(a) Apply couplant to the calibration standard, and smooth the couplant with your
finger to produce a uniform thin layer.
(b) Place the POSITIONER on the calibration standard, and insert the
TRANSDUCER in the “S” guide hole until it bottoms. Align the transducer
with the lower OD EDM notch.
(c) Identify the signal received from the notch, and adjust the gain to obtain 100%
FSH. Reference Figure 1 for a CRT display of the calibration notch.
Figure 1. “S” scan calibration notch signals
(2)
INSPECTION PROCEDURE
(a) Do to the increased angle of inspection additional signals are received within
the gate. Reference Figure 1 to assist with signal interpretation. Damp
signals on the calibration standard with a finger moistened with couplant to
gain familiarity.
(b) This inspection technique focuses the sound beam on the ID mid-shank of the
bolt but will detect ID and OD cracks at other locations.
(a) Place the positioner on the bolt to be inspected, slowly rotate the
positioner making two passes with the “S” scan.
(3)
ACCEPTANCE/REJECTION CRITERIA
ID or OD cracks can appear anywhere within the gated area. The signal received
from a small crack will usually have a very quick rise and fall time when scanning.
Any relevant signal exceeding the gate threshhold is rejectable.
Lower OD
Shoulder
