CHAPTER 9
ULTRASONIC
TESTING OF ALUMINO THERMIT WELDED JOINTS
(Chapter revised vide ACS
No.6 of 1999)
9.1 Scope
: This procedure covers the requirement of ultrasonic testing of alumino
thermit (AT) welded rail joints immediately after execution of the weld and
also for periodic examination.
9.2 General conditions of test
9.2.1 Surface preparation: After execution of the
AT weld, the welded zone shall be dressed properly to facilitate placement of
probes and to avoid incidence of spurious signals on the CRT. The rail table
shall be dressed to obtain reasonably
flat and smooth surface. The
flange and the web up to a distance of 200 mm on either side of the
weld collar shall be thoroughly cleaned with a wire brush to ensure freedom
from dust, dirt, surface unevenness etc. (ACS No.6 of 1999)
9.2.2 Couplant
: Water/oil /soft grease shall be used as couplant. (ACS No.6 of 1999)
9.2.3 Sensitivity : The
equipment sensitivity shall be set for normal, 70
and
70,
1.25 MHz probes in accordance with the
procedure laid down in para 9.4. The sensitivity so adjusted shall be
considered as normal gain sensitivity and shall be utilised during ATW testing.
The sensitivity level shall not be altered during the course of testing. (Para 9.2.3 revised vide ACS
No.10 of 2002 by superceding ACS
No.6 of 1999)
9.3 Apparatus required
9.3.1 Equipment: Any model of RDSO approved
rail tester shall be considered suitable for testing of AT welded rail joints.
9.3.2 Probes: During
ultrasonic examination of AT welded joints, the following probes shall be
utilized :
a. Normal
(0),
4 MHz -Double crystal fitted in
trolley.
b.
70,
2 MHz -Double crystal
fitted in trolley.
c.
70,
2.0 MHz -Single crystal for hand probing
9.3.3
Cable : One co-axial cable of suitable length for
connecting 70,
2.0 M.Hz probe to flaw detector shall be used.
The length should not exceed more than 5 m. (Paras
9.3.2 and 9.3.3 revised vide ACS No.10
of 2002 by superceding ACS No.6 of
1999)
9.4 Sensitivity setting procedure
9.4.1
Calibration : The equipment should be set
for a depth range of 300 mm (longitudinal wave) by adjusting depth control knob
suitably. Each division, therefore, shall correspond to 30 mm. (longitudinal
waves) (Para 9.4.1 revised vide ACS No.10 of
2002 superceding ACS No.6 of 1999)
9.4.2
Test rail: The sensitivity of the ultrasonic equipment shall
be set with the help of a standard AT welded rail piece of 1.5 m length having
a simulated flaw at standard locations as shown in Fig. 17.
9.4.3
Alignment of probes : The
alignment of normal and 70
probes fitted with the trolley may be checked by placing the rail tester on
the test rail using water/oil as couplant and ensuring that the
probes travel along the vertical axis of the rail.
9.4.4
Sensitivity setting
9.4.4.1
Place the trolley on the test rails shown in fig. 17. Keep the switches
of all the probes in off positions and turn the potentiometer knobs of all the
probes to 50% of their highest working range.
9.4.4.2
Switch on only 70forward
probe and move the equipment towards the drilled hole of 3 mm dia in the rail
head. When the probe is just in the reflecting range, a pulse corresponding to
the hole shall appear on the screen which during onward travelling shall show
higher amplitude. The pulse shall appear moving from right to left The
equipment should be progressively moved forward till maximum height of the
pulse is obtained. At this location, the height of the pulse shall be adjusted
to 60% of full screen height by suitable manipulation of the gain knob.
9.4.4.3
The forward probe shall be switched off and the 70%
backward probe shall now be switched on. In this case a flaw signal shall
appear moving from left to right. The signal height in this position shall also
be adjusted to 60% of full screen height. This can be accomplished through
suitable manipulation of relevant potentiometer.
9.4.4.4 The sensitivity setting
for the normal probe has to be done while keeping all other probes in off
position. Switch on only the normal probe and bring it above 3 mm dia hole at
head of the test rail. Manipulate the potentiometer control knob to obtain echo
height of 60% of full screen height at 1.0 division horizontal scale.
9.4.4.5
70,
2.0 MHz
probe shall be connected to the socket available in the ultrasonic
equipment The selectors switch may be set to single crystal mode. Move the
probe towards the 3 mm dia hole drilled at the middle of flange through the AT
weld and manipulate knobs to obtain a
60% full screen height on the CRT.
9.5
Criteria for defect classification for
initial testing
9.5.1 Till
such time more exhaustive studies are carried for strengthening the initial
testing of AT welds, any flaw signal
obtained by normal probe in the head of 40% height or more shall be treated as
a defective AT welded joint. Any flaw signal
of 10% height or more obtained
from the normal probe either from the web or the foot location shall also be a
cause for rejection of the AT weld. (Paras 9.4.4.5 and 9.5.1 revised vide ACS No.10 of
2002 by superceding ACS No.6 of 1999)
9.5.2
In the case of lack of fusion, inclusions, blow holes etc, in the rail head,
moving signal shall be obtained while testing with 70probe.
The position of onset of the signal and its corresponding range on the
horizontal screen as well as their maximum amplitude shall be recorded.
A
welded joint showing the moving signal of 40% or more of the full screen height
shall be considered as a defective welded joint.
9.5.3 70,
2.0 MHz
probe shall be placed on the flange at a distance of 180 mm corresponding to position 'L' in Fig. 18 such
that ultrasonic waves are directed towards the weld. The probe shall thereafter
be moved slowly in a zigzag pattern towards the weld. A welded joint showing a
flaw echo of 40% vertical height or more with the stipulated gain setting shall
be treated as a defective welded joint. Similar testing shall be carried out
from 'C' and 'U' region as shown in Fig. 18.
In these cases also the criteria for rejection shall remain the same. (Para
9.5.3 revised vide ACS No.10 of
2002 superceding ACS No.6 of 1999)
9.6 - A thermit welding done in-situ shall
be joggled fish plated with four clamps and supported on wooden blocks till
tested as good by USFD" (ACS No. 6 of 1999)
9.6.1 The defective joints based on the criteria
mentioned at para 9.5 shall not be allowed to remain in service and these
joints shall be cropped, re-welded and tested again. This execution shall be
done by the contractor free of cost. The re-welded joints shall be scanned
ultrasonically again with the same set of acceptance criteria to ensure freedom
from any harmful detects.
9.7
Periodic testing of welds in service
9.7.1
Testing with 0
and 70probes
: During on track periodic testing of AT welded rail joints gain setting shall
be done in respect of 0
and 70angle
probes on standard test rail, (need based/conventional as the case may be) as
applicable for rail testing (Refer Fig. 3 and 4).
9.7.1.1 The testing of weld using 0
and 70probe
shall be conducted with the help of rail test trolley during routine rail
testing.
9.7.2
Testing with 70,
2.0 MHz
probe (Flange testing): Gain setting of the USFD equipment during
testing shall be such that a flaw peak height of 80% of full screen height is
obtained from 3 mm dia hole at the flange through the AT weld (Fig. 17).
9.7.2.1 The
testing of the flange using 70,
2.0 MHz
probe shall be conducted in the same manner as outlined for testing of
new AT welds (Para 9.4.4.5). (Para 9.7.2 and 9.7.2.1
revised vide ACS No.10 of 2002 by superceding ACS No.6 of 1999)
9.8 Criteria for
classification of defective joints based on 0and
70probe
shall be as per Annexure IV for testing with conventional criteria and as per
Annexure VII for need based criteria.
9.9 Criteria for classification of defective
joints in the flange location tested by 70,
2.0 MHz
probe shall be as per Annexure V for conventional testing and as per
Annexure VII for need based concept of USFD testing. (Para
9.9 revised vide ACS No.10 of 2002 by superceding ACS No.6 of 1999)
9.10. Procedure
for detection of half noon cracks in AT welds.
9.10.1 Preamble: Half moon cracks are found to be present in the
rail foot centre of AT welds and are oriented transversely. In AT welds these defects are associated
with fins formed during AT welding. For
avoiding such defects and consequent failure in service, the following
procedure shall be followed :
9.10.2 Procedure: All
AT welds in service are required to be examined visually and through ultrasonic
examination for detection of cracks emanating from rail foot. Visual examination can be carried out by
PWI/USFD or sectional PWI and USFD examination shall be carried out by
PWI/USFD. The procedure for visual and
USFD examination shall be as under.
9.10.3 Visual Examination: All the welded joints shall be cleaned and
examined carefully to detect any visible defects like cracks, blow holes,
shrinkage, mismatch, surface finish (smooth surface required) etc. Any joint which shows visible defect shall
be declared defective.
The bottom of the joint shall
be checked by feeling with fingers as well as inspected with the help of a
mirror for presence of fins at the parting line of the mould. If fin is observed in any joint, the joint
shall be declared defective.”
9.10.4.
Ultrasonic Examination
9.10.4.1
Scope-This procedure covers the
requirements of ultrasonic examination of Alumino-Thermic joints for detection
of half moon cracks emanating transversely from the centre of the rail foot.
9.10.4.2
Apparatus required:
9.10.4.2.1
Equipment-Any RDSO approved equipment
meeting the requirements of RDSO
specification.
9.10.4.2.2 Probes: The following probes shall be used for
Ultrasonic Examination of AT welded joints.
(i)
Normal (0—),
2 MHz 18mm PZT double crystal probe for calibration.
(ii)
45—
/2MHz, 20mm x 20mm PZT crystal forward and backward probe housed in one
assembly or single 45—
/2 MHz, 20mm x 20mm PZT crystal probe.
(iii)
70—
/2 MHz, 8mmx8mm, PZT crystal probe-1 Nos.
9.10.4.2.3 Cables: Coaxial cable for each probe shall be
used. The length shall be approximately
2 metre.
9.10.4.2.4 Couplant: Soft
grease/Oil/water shall be used as couplant.
9.10.4.3 General condition of test: The welded zone of the joint shall be dressed
on all sides properly to facilitate placement of probe and to avoid incidence
of spurious signals on the CRT. The head surface shall be dressed to obtain
reasonably flat and smooth surface. The
outer faces of the flange shall also be clean and smooth.
9.10.4.4. Standard Test Piece: Standard A.T. welded rail piece of 1.5 metre
length with AT joint in the middle having simulated flaw as shown in fig.36.
9.10.4.5
45º forward and Backward probe
9.10.4.5.1 Range calibration: The equipment shall be set for depth range
of 500mm for longitudinal wave using 0—
probe.
9.10.4.5.2 Sensitivity setting: Place 45—
/2MHz (F&B) probe or 45—
/ 2MHz probe on the rail head surface at a distance equal to height of rail
from the centre of the AT weld Move the probe 40mm either side of this position
to pick up half moon crack at lower fins on zone of the flange. This exercise shall be carried out twice,
once from each side of the weld and signal from simulated flaw as shown in fig. Should appear at a distance approx 400mm for
52 kg rail. This distance will vary
with respect to rail section height.
The signal so obtained shall be adjusted to 60% of full screen height by
manipulating the gain control knob.
9.10.5 Test Procedure: The probe 45—
/2MHz (F&B) probe or 45—
/2MHz single probe shall be placed on the railhead of AT weld under test with
same sensitivity as per para 9.10.4.5.2.
This testing technique will scan the bottom of the flange weld in the
central zone. If 45 —
2MHz single probe is used the scanning shall also be done from one side of
railhead of the weld with beam directing towards the web foot region of the
weld. 45—
/ (F&B) probe shall be moved on the railhead table crossing the weld region
on the other side as shown in fig.37.
9.10.6 70— /2MHz, size
8mm x 8mm probe. This technique shall
be used when due to presence of hole in
the web; the above procedure is no possible to adopt.
9.10.6.1 Range calibration: The equipment shall be set for a depth
range of 300 mm (longitudinal wave) by manipulating the depth control knob
suitably.
9.10.6.2. Sensitivity Setting: One
70—/2
MHz, size 8mmx8mm probe shall be connected to the unit by means of one coaxial
cable. The selector switch shall be in
T+R (single crystal) mode. Apply the
couplant and place the probe at a distance of 100 mm from edge of the weld near
to root of the flange with beam direction towards simulated flaw. Move the probe slightly in zigzag manner to
get reflection from simulated flaw. Set
the height of signal to 60% of full screen height. The gain level will be utilized during testing.
9.10.6.3 Test Procedure: 70—
probe shall be placed on the root of the flange at a suitable distance (100mm
approx) with beam directing toward web-foot junction and scanning shall be
carried out as per para 9.10.6.2. This
exercise shall be carried from all the four sides of rail flange and any moving
signal on the screen shall be recorded.
The method is not capable of
detecting all half moon defects due to its position of probing.
9.10.7 Defect Classification: Any
flaw signal of height 10% or more than
of the full screen height shall be considered as defective AT weld in both the
technique applied for 45—
and 70º probes. and shall be classified as DFW.
(New para 9.10 introduced vide ACS No.
12 of 2002)
(Underlined extension done in para 9.10.7 vide ACS No.13 of 2003)