IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
Table 1 : Different parameters to be considered for immersion TOFD
which were earlier confirmed
through radiography. The
combination of TOFD and
immersion could pick up these
defects, which was not possible
with conventional TOFD
method. Typical TOFD images
are shown in Fig. 2 (c) and 2(d)
respectively. The welded
specimens were subjected to
radiography and the
radiographic images were
processed with appropriate
methodologies and dimensions
of the defects estimated.
Dimensional measurements
from radiographs were
compared with the dimensions
from TOFD measurement. A
very good correlation was
obtained with errors being less
than 5%.
This experiment establishes
that TOFD combined with
immersion extends the limits of
examination of conventional
TOFD and is a novel solution
for the examination of thin
weldments.
V.A.2. Infra Red Thermal Imaging of Weld Pool in
Real Time during GTAW of Type 316 LN Stainless Steel
In remote welding operations,
on-line monitoring and control
of Gas Tungsten Arc Welding
(GTAW) process is very
essential and a methodology is
being established using IR
Thermography. The infra red
camera was mounted on the
torch assembly to facilitate online
monitoring of the welding
process and determine surface
temperature distribution
surrounding the weld pool
during GTAW. The interference
from the arc light and the hot
tungsten electrode on the
image quality is minimized by
using band pass filters. The
instantaneous thermal images
of the weld pool that were
captured by the infra red
camera was transferred to a
computer. The infra red camera
determines the surface
temperature distribution of the
plate by capturing the emitted
energy within a wavelength
band of 4 - 6 µm. Each scan of
the camera was transferred as a
frame consisting of
320 x 240 discrete temperature
measurements. Full frame
analysis was carried out to
determine the temperature
surrounding the weld pool for
the entire length of the plate
being welded and is shown in
Fig. 1. This data was very useful
in validating the heat flow
118 ENABLING TECHNOLOGIES