AT welding in Railway track, INDIAN RAILWAYS

1. QUALITY IMPROVEMENT IN AT WELDS
 AT Weld failures continue to haunt the Indian
Railways. These failures are of serious concern as
each weld failure has the potential to cause a
derailment and also they lead to disruption to traffic
and reduce effective line capacity. Statistics shows
that failures of alumino-thermic welds account for 90
to 95% of total weld failures and approximately 34%
of AT welds failures are of welds younger than five
years, there is certainly a need to look ahead and
identify deficiencies. New techniques adopted in
recent years such as combination joints and wide gap
welding have aimed at removing some of the
handicaps in the in-situ welding of rails. But there has
been no major improvement in the technology for AT
welds in the last decade. Hence, there is tremendous
potential to improve the quality of AT welds.

2. AT WELDS DONE/DEFECTIVE REPORT INDIAN RAILWAYS LOCATED ON : ALL LINES
PERIOD : 01/01/2014 - 25/08/2019
Railway Division
No. of
AT Welds Done
No. of
AT Welds Tested
No. of
AT Welds
Untested
No. of
Defective AT
Welds
Defective Welds
(%)
CR BSL 35998 28854 7144 2383 8
CR CSTM 19920 15285 4635 1744 11
CR NGP 36692 29559 7133 4037 14
CR PA 19947 13504 6443 1525 11
CR SUR 25103 19105 5998 2387 12
CR Total 137660 106307 31353 12076 11
ECOR KUR 47787 26773 21014 7317 27
ECOR SBP 28667 17166 11501 2142 12
ECOR WAT 70741 42450 28291 3115 7
ECOR Total 147195 86389 60806 12574 15
ECR DHN 18334 12803 5531 1837 14
ECR DNR 15610 9564 6046 1142 12
ECR MGS 15213 9489 5724 1013 11
ECR SEE 20212 8488 11724 2562 30
ECR SPJ 4114 2909 1205 259 9
ECR Total 73483 43253 30230 6813 16
ER ASN 23795 19354 4441 1544 8
ER HWH 29265 22938 6327 2214 10
ER MLDT 12966 10267 2699 322 3
ER SDAH 19637 14678 4959 682 5
ER Total 85663 67237 18426 4762 7
MR MRD 2 0 2 0 0
MR Total 2 0 2 0 0
NCR AGC 24842 21486 3356 5232 24
NCR ALD 42483 37436 5047 5653 15
NCR JHS 26208 19891 6317 1889 9
NCR Total 93533 78813 14720 12774 16

3. AT WELDS DONE/DEFECTIVE REPORT INDIAN RAILWAYS LOCATED ON : ALL LINES
PERIOD : 01/01/2014 - 25/08/2019
NER BSB 28494 12944 15550 2166 17
NER IZN 11536 7653 3883 1038 14
NER LJN 20023 14163 5860 1845 13
NER Total 60053 34760 25293 5049 15
NFR APDJ 29701 22221 7480 1805 8
NFR KIR 19303 11913 7390 885 7
NFR LMG 25224 12206 13018 416 3
NFR RNY 14516 8104 6412 37 0
NFR TSK 6910 2563 4347 54 2
NFR Total 95654 57007 38647 3197 6
NR DLI 53686 47365 6321 9244 20
NR FZR 23473 20028 3445 2175 11
NR LKO 41149 32455 8694 4842 15
NR MB 54917 49642 5275 9213 19
NR UMB 38613 33149 5464 4975 15
NR Total 211838 182639 29199 30449 17
NWR AII 14318 9628 4690 1626 17
NWR BKN 17573 15828 1745 3259 21
NWR JP 22942 18120 4822 2000 11
NWR JU 19541 16447 3094 1913 12
NWR Total 74374 60023 14351 8798 15
SCR BZA 51014 42437 8577 4973 12
SCR GNT 19320 15079 4241 3801 25
SCR GTL 46746 37203 9543 4200 11
SCR HYB 11456 9077 2379 809 9
SCR NED 7863 6271 1592 288 5
SCR SC 49146 41184 7962 966 2
SCR Total 185545 151251 34294 15037 10
SECR BSP 45955 33779 12176 7933 23
SECR NAG 36431 26894 9537 5931 22
SECR R 32286 21554 10732 5303 25
SECR Total 114672 82227 32445 19167 23

4. AT WELDS DONE/DEFECTIVE REPORT INDIAN RAILWAYS LOCATED ON : ALL LINES
PERIOD : 01/01/2014 - 25/08/2019
SER ADA 22222 17177 5045 1626 9
SER CKP 33468 22974 10494 6383 28
SER KGP 32508 21477 11031 852 4
SER RNC 9675 7621 2054 1223 16
SER Total 97873 69249 28624 10084 15
SR MAS 19030 13410 5620 1612 12
SR MDU 16352 12300 4052 1188 10
SR PGT 23413 17154 6259 2306 13
SR SA 19497 16544 2953 2214 13
SR TPJ 14751 10760 3991 1057 10
SR TVC 23407 16207 7200 1147 7
SR Total 116450 86375 30075 9524 11
SWR MYS 13518 10638 2880 1755 16
SWR SBC 26231 21586 4645 4309 20
SWR UBL 18592 13715 4877 1054 8
SWR Total 58341 45939 12402 7118 15
WCR BPL 39929 30988 8941 5544 18
WCR JBP 54999 38715 16284 3478 9
WCR KTT 43392 35462 7930 6814 19
WCR Total 138320 105165 33155 15836 15
WR ADI 31124 26455 4669 2824 11
WR BCT 37686 30224 7462 2538 8
WR BRC 26462 20968 5494 2141 10
WR BVP 5751 4702 1049 283 6
WR RJT 17267 14217 3050 780 5
WR RTM 35584 29429 6155 3063 10
WR Total 153874 125995 27879 11629 9
Total 1844530 1382629 461901 184887 13

5. PROCEDURES FOR ALUMINOTHERMIC
WELDING
The rails are cut square and the gap to be
welded is prepared within prescribed limits1. (If
the rail ends are cut skewed, the gap will be non-
uniform and the fusion of the rails will be
asymmetric.)

6.  The cut faces are cleaned with kerosene oil
and a wire brush to remove rust, dust, or
greasy material, etc. (Otherwise, this material
may get fused with the weld material and this
may render the weld defective.)

7.  A 1m-long steel straightedge is used to align the
running edge2 of the rail head. The rail ends are
'peaked' to accommodate contraction during
solidification and cooling of the 'Thermit' steel. If
'rising' of the rails is not done, the joint will sag
due to differential cooling of the rail head (where
more material is available and hence the cooling
is slower) and rail foot after cooling. A sagged
joint gives bad riding and becomes a
maintenance problem. Such a joint will be
subject to larger stresses due to the dynamic
augment. For lateral and vertical alignment,
wedges are used.

8.  Stands for crucible and torch are fixed on the
railhead, at appropriate locations, on
opposite sides of the welding gap and
position and the height of the torch stand is
checked and adjusted by placing the
preheating burner or welding torch on it
which is then removed and set aside for later
use.

9.  A set of prefabricated moulds of the appropriate rail section is
selected and examined for suitability3. The rail profile of the mould
is checked4 by placing the mould against the side of the rail to be
welded. If required, small adjustments to the mould profile are
made by rubbing the mould gently against the sides of the rail.
Then the moulds are placed in the mould shoe (i.e., clamp),
seating it properly using luting sand. The placement of the mould
should be central over the gap as otherwise while pouring the
molten metal, one rail end will get more heat than the other and
the fusion of the metal at the other rail end may not be complete.
The recess, if any, between the mould and the rail profile is
sealed with luting sand. A slag bowl is attached to the mould shoe
to collect the overflowing slag and molten metal during the
pouring.

10.  The magnesite lines crucible is housed at the
correct height and alignment on the swiveling
crucible stand. A closing pin is placed at the
bottom over the opening. This pin's head is
covered by about 5g of asbestos powder, so
that it does not melt in contact with the
molten metal and 'auto tapping' takes place.

11.  The crucible is swung away from the rail and
the 'portion' (self-igniting mixture which yields
the molten metal) is poured into the crucible,
heaped in a conical shape.

12.  Using LPG (commercial use cylinders) and
oxygen (or petrol and compressed air, an
older technique, but still in use), the
preheating burner or welding torch is lit and
the flame is tuned. This torch is placed in its
stand which is fixed over the gap, and the
flame is directed into the mould through the
central opening. The flame heats the rail
ends and this is done for a specified time for
each rail section and the pre-heating gases
employed.

13.  As the preheating is completed, the Thermit
reaction is initiated by igniting a sparkler and
putting it into the crucible. The reaction is
allowed a specified time and the slag is
allowed to be separated from the molten
metal. Thereafter, the closing pin is tapped
from the outside, thus discharging the metal
into the top central cavity of the mould.
Thereafter, the crucible and torch stands are
removed.

14.  The excess Thermit steel over the head of
the rail (head riser) is removed after
solidification (but when the metal is still red
hot) by either manual chiseling or using
hydraulic weld trimmers.

15.  The remaining refractory material is removed
and the steel vent risers attached to the
collar of the foot of the weld are snapped off.

16.  The wedges, etc., are removed, any
fastenings that were removed, are re-fixed
and the railhead is ground manually or using
grinding machines.

17. Time for each activity
Nominal Gap 25mm gap 50mm gap 75mm gap
Gap Width 25±1mm 5±1mm 75±1mm
Portion weight — 52kg section
(kg)
10.8 13.5 22
Vertical alignment, either side of
1m straightedge
1.0-1.25mm high 1.25-1.50mm high 2.5-3.0mm high
Lateral alignment (gauge side),
at end of 1m straightedge
0-0 0-0 0-0
Heating time with petrol and air
at 100-110 psi, 7-7.7kg/cm2
(minutes)
10-12 18-20 20-25
Heating time with LPG at 2.0-
2.5kg/cm2 and O2 at 7-8kg/cm2
(minutes)
2.0-2.5 2.5-3.0 3.0-4.0
Heating time with petrol and
compressed air at 0.2-0.3
kg/cm2 (minutes)
5.0-5.5 10-11
Reaction time (seconds) 20±3 20±3 25±5
Mould waiting time (minutes) 04-05 06-07 10-12
Chipping time — manual
(minutes)
4 05-06 08-09
Chipping time — weld trimmer
(minutes)
0.5-1 0.5-1 0.5-2
Train passing time after pouring
(minutes)
30 30 30
Vertical tolerance for finished
weld
�0.4mm at centre of 10cm
straightedge
�0.4mm at centre of 10cm
straightedge
�0.4mm at centre of 10cm
straightedge
Lateral tolerance for finished
weld
0-0.3mm at centre of 10cm
straightedge
0-0.3mm at centre of 10cm
straightedge
0-0.3mm at centre of 10cm
straightedge

18. THERMIT REACTION PRINCIPLE
 Thermit reaction details Aluminium reacts
with iron oxides, particularly ferric oxide, in
highly exothermic reactions, reducing the
iron oxides to free iron, and forming a slag of
aluminium oxide.
 3Fe3O4+ 8Al = 4Al2O3+ 9Fe (3088°C,
719.3kCal↑)
 3FeO + 2Al ⇒ Al2O3 + 3Fe (2500°C,
187.1kCal↑)

19. RAIL AND GAP RELATED
 Rail ends should be cleaned with wire brush and
K.oil.
 Gap at rail joint prior to welding should be as
under : SPW = 25 ± 1 mm
Wider gap welding = 75 ± 1 mm
 Ensure correct alignment of rails prior to
welding. The joint shall be kept higher by 3 to 4
mm for 72 UTS rails and 2 to 2.4 mm for
higher UTS rails when measured at the end of
1m straight edge.

20. MOULD RELATED
 Ensure that prefabricated moulds are as per the
welding technique, free from any moisture and
cracks.
 10. Prefabricated mould should be dressed w.r.t.
actual rail profile being welded prior to their
fixing.
 11. Prefabricated mould should be centrally
fixed and centre lines of two halves of
prefabricated moulds should coincide with each
other.
 12. Ensure that mould shoe are in proper

21. MOULD AND LUTTING RELATED
13. Prefab mould/ shoe should be gently
pressed to ensure flush fitting.
 14. The gap between mould and the rail
should be packed firmly with luting sand to
prevent leakage of liquid weld metal.
 15. Ensure that no foreign elements should
be mixed in luting sand.

22. HEATING RELATED
 For proper and uniform preheating of both
rail ends, vaporiser should be placed at
proper height. Maximum height of Goosen
neck from rail top should be 40mm.
 17. Ensure that crucible is properly dried/
changed and repaired prior to pouring of
portion.

23. CRUCIBLE RELATED
 Ensure that thimble is dry & free from moisture
and thimble shape is round and dia is as under :
 72 UTS rails - 14mm to 16mm 90 UTS rails -
18mm to 20mm
 Max. height of crucible from top of prefabricated
mould should be 50 mm.
 Workability of pressure gauge fitted on petrol
tank in case of air petrol heating and gauge
fitted on oxygen & LPG cylinders in case of
preheating with OxyLPG mixture, should be
checked before carrying out welding of rails.

24. PORTION RELATED
 Ensure that portion bags are properly sealed &
intact at the time of opening.
 22. 90UTS portion should be used when
welding of 72 UTS & 90 UTS rails is being done
under unavoidable circumstances.
 23. Portion being used should not be more than
2 year old provided packing is intact and there is
no entry of moisture.
 24. Portion should be properly stored at the site
of welding so as to prevent entry of moisture

25. REACTION RELATED
 Ensure proper plugging of crucible
 27. Portion should be thoroughly mixed in the pan
before pouring it into the crucible for ignition.
 28. Ensure reaction time of ignition of portion as 20 ±
3 seconds and portion in the crucible should be
covered by crucible cap.
 29. Molten metal should be tapped within 20 ± 3
seconds after start of reaction.
 30. In case of 90 UTS rails, controlling of cooling
should be ensured by post heating of rail & flange
upto 50 cms on either side of mould box with the help
of vaporisor.

26. POST WELDING RELATED
 Bottom half of prefab mould should be
preserved at the time of demoulding to
ensure controlled cooling.
 Chipping of hot metal should be done within
4 to 5 minutes of pouring of molten metal into
the gap with the help of weld trimmer.

27. FINISHING RELATED
 Ensure final finishing of joint within 24 hours of
its execution, to the following tolerances.
 a) Vertical alignment +1 mm (at the end
of 1.0m - 0 mm straight edge)
 b) Lateral alignment = ± 0.5mm on 1.0 m
straight edge.
 c) Finishing on sides of head of welded joint
= ± 0.3 mm on 10cm straight edge
 d) Finishing at top table surface + 0.4 mm (at
the end of 10 cm - 0.0 mm straight edge).

28. POST WELDING RELATED
 Ensure that there is no chisel mark on rail
surface after final finishing.
 Ensure that 100m on either side of weld is
destressed at the time of permanent repairs in
LWR/ CWR panel as per instructions laid in
LWR manual 1996.
 Moreover weld collars should be painted.
 Ensure that trimming of all new welds are done
with the help of weld trimmer and grinding with
the help of weld profile grinding trolley.

29. DON’TS OF AT WELDING OF RAILS
 1. No ultrasonically untested rail should be welded.
 2. No A.T. welding should be carried out by
incompetent staff.
 3. Don’t weld second hand rail without its end
cropping.
 4. Don’t cut the rails by flame cutting.
 5. Don’t weld rails having battering/ hogging and
without cleaning rail ends with wire brush and K. Oil.
 6. Don’t weld rails having bolt holes at the ends.

30. DON’TS OF AT WELDING OF RAILS
 Don’t use consumable items like portion, luting sand
if their validity has expired.
 8. Don’t use worn out and defective welding
equipments.
 9. Don’t carry out in-situ welding during inadequate
traffic block.
 10. Don’t use damaged prefabricated moulds.
 11. Don’t add any extra material in the premixed
luting sand.
 12. Don’t use loose portion.
 13. Don’t add or subtract any material from the
portion.

31. DON’TS OF AT WELDING OF RAILS
 14. Don’t carry out welding in rain.
 15. Don’t pour portion into the crucible without mixing
it properly in the pan.
 16. Don’t pass the first train over newly welded joint
without its rough grinding joggle fish plating and
wooden block support, in case of in-situ welding.
 17. Don’t pass the train before 30 minutes after
pouring the molten metal.
 18. Don’t carry out welding at incorrect pressures of
compressed air petrol mixture, O2 and LPG (in case
of OxyLPG preheating)

32. DON’TS OF AT WELDING OF RAILS
 19. Don’t remove/ loosen the wedge used
for aligning the rail ends prior to 20
minutes after trimming i.e. prior to weld
had fully cooled down. (MOST
IMPORTANT). 20 min time starts after
stripping not pouring.
 20. Don’t remove/ loosen the rail tensor prior
to weld has fully cooled down.
 21. Don’t store the portion at a place having
dampness.

33. PAINTING OF WELD COLLAR
 Painting of weld collar should be done on
all the welds to protect them against
corrosion immediately after the welding.
 In service, painting of thermit welds should
be carried as per following frequency :
 Once in four years in areas not prone to
corrosion.
 Every year at locations prone to corrosion.

34. PAINTING PROCEDURE FOR NEW WELDS
 In normal areas
 After surface preparation, one coat of ready
mixed paint, brushing bituminous black
conforming to IS: 9862-1981 is applied on the
welded area upto 10 cms on either side. After
eight hours drying, also a second coat of the
same paint is applied. In corrosion prone
areas
 After surface preparation, one coat of high build
epoxy paint (two pack) conforming to RDSO
specification No. M&C/PCN111/88 is applied on
the welded area up to 10 cm on either side.

35. MAJOR DEFECTS IN AT WELDING
Major Defects in AT Welding
 The common defects in thermit
welds due to deficiency in
execution are as under:
 a) Lack of Fusion
 (i) Causes
 Improper cleaning of rail
ends.
 Inadequate or non-uniform
pre-heating
 Inadequate or non-uniform
gap.
 Delayed tapping.
 This is serious defects and
makes the weld weak.

36. PREVENTIVE ACTION FOR LACK OF FUSION
 (ii) Preventive Action for lack of fusion
 Maintain the welding gap between rail ends specified in the approved
parameters of the technique. Never attempt to weld a gap, which is too
wide, with standard mould.
 Take care to centralise the mould to the gap. Never try to fit both
mould halves simultaneously.
 Take care to fit mould both vertical and central to the weld gap. Do not
incline mould to the vertical.
 Do not try to weld worn to new rail, or rails dissimilar depth with
standard mould.
 Rail ends should be properly cleaned.
 The tapping shall be done within the time specified for that particular
technique.
 Special care shall be given to the tank pressure, efficiency of burner
and flame condition for achieving required rail temperature within the
stipulated time.

37. MAJOR DEFECTS IN AT WELDING
 b) Slag inclusion
 (i) Causes
 Early tapping.
 Pouring without plug in
position.
 (ii) Preventive Action
 After preheating fit the sand
core with the riser aperture of the
mould and press down lightly.
 Ensure that the crucible is
positioned centrally the over the
sand core and the crucible does
not move during the thermit
reaction.
 Never allow the thermit steel to
pour directly into either pouring
gate.

38. MAJOR DEFECTS IN AT WELDING
 c) High porosity in weld
metal (gross/local)
 (i) Causes
 Use of damp crucible. Use
of damp mould. Use of
damp portion.
 (ii) Preventive Action
 Crucible must be pre-heated
before first weld of the day to
remove any moisture.
 Damp portions and damp
moulds should not be used in
welding.

39. MAJOR DEFECTS IN AT WELDING
 d) Sand Inclusion
 (i) Causes
 Dropping of luting sand into mould. Broken
pieces of mould getting into the mould.
 (ii) Preventive Action
 Take care when sealing the mould with luting
sand. It must not be allowed to drop into the
mould. If the welder is careful, these defects can
be easily avoided.

40. DEFECTS IN AT WELDING

42. DEFECTS IN AT WELDING

43. PRECAUTIONS TO AVOID DEFECTS IN AT WELDED RAIL JOINTS
 (i) It should be ensured that the portion being used matches with type and
chemistry of rail.
 (ii) Rail ends should be square.
 (iii) Alignment of rail ends should be perfect as checked by straight edge.
 (iv) Rail ends should be properly cleaned with kerosene oil and wire brushes.
 (v) Stop watch should be provided to the welding supervisor at each welding
site.
 (vi) Pressure in the tanks/cylinder should be properly maintained during pre-
heating.
 (vii) Correct gap between rail ends at head, web and foot shall be ensured.
 (viii) Correct preheating time for rail ends shall be ensured.
 (ix) Tightness of clips fitted with hose connections to compressor tank and
burner shall be checked before commencing preheating.
 (x) Nozzles of burners shall be cleaned periodically to avoid back fire.
 (xi) The tapping shall be done within the time specified for that particular
technique. For special type of welding i.e. 75mm gap, combination joint etc. the
time of reaction and tapping shall be as stipulated by RDSO for that particular
welding technique.
 (xii) Boiling portion shall be tapped outside the welding gap
 (xiii) No moist portion/ torned bag portion shall be used for welding.

44. PRECAUTIONS TO AVOID DEFECTS IN AT WELDED RAIL JOINTS
 (xiv) Dampness in moulds can lead to porosity and early fatigue
failure of welds.
 (xv) Only those contractual agencies as have clearance from the
RDSO/Railway Board can execute welding work. Supply of
portions must be from sources approved by RDSO/Railway
Board.
 (xvi) Many weld failures show evidence of badly cut rail ends.
The evenness and verticality of a rail cut depends solely upon the
skill of the welder. With portable disc cutters, less skill is required
to produce good cut.
 (xvii) A Thermit weld done in situ shall be joggle fish plated.
(para 502 of IRPWM & USFD Manual Revised -2012). Anti
corrosive painting of all the Thermit welds should be carried out
as per provision of manual for fusion welding of rails by AT
process.
 (xviii) The compressor tank shall be kept 2 to 3 meter away from
heating torch to prevent fire hazard.
 (xix) Welders should be provided with gloves and coloured
glasses.

45. HALF MOON DEFECT IN AT WELDS
 DETECTION OF
HALF MOON CRACK IN AT
WELDS Half moon cracks are
found to be present in the rail foot
center 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,
procedure laid down for visual
examination by sectional
SSE/JE/P.Way and USFD
examination by SSE/P.Way /
USFD as per para 8.7 and 8.1 (b)
of USFD manual revised -2012,
should be followed.

46. PRECAUTIONS AND PREVENTIONS DURING MAINTENANCE OF TRACK GENERALLY FOR
WELD FAILURE IN WINTER SEASON
 (i) Do De-stressing of LWR/CWR whenever due. Special
attention should be given to the location where high temperature
de-stressing was done for BCM or other planned work and de-
stressing to be done again at appropriate temp.
 (ii) Duty hours of Keymen should be changed so that failures, if
any, can be detected in time. Keymen and patrolmen should be
suitably trained to detect fractures and to take protective
measures.
 (iii) Weld Fracrture prone locations of LWR/CWR should be
identified and measures like recoupment of missing fitting and de-
stressing at lower temperatures for winter season may be taken
as per requirement.
 (iv) It should be ensured that there are no arrears of USFD
testing.
 (v) All Arrangements for cold weather patrolling should be made
as per para 9.1.2 (ii) of LWR Manual.

47. PRECAUTIONS AND PREVENTIONS DURING MAINTENANCE OF TRACK GENERALLY FOR WELD
FAILURE IN WINTER SEASON
 (vi) A close watch on rail temperatures should be kept and temperature
record register should also be maintained by the SSE (P-Way).
 (vii) Rails having corroded flange should be kept under special watch.
 (viii) Inspection of LWRs/CWRs & SEJs by SSE/JE (P-Way) as per
para 8.1.5(i) of LWR Manual.
 (ix) DFWR welds more than three month old to
be removed either by replacing the rail or by 75
mm gap AT welding. (As per para 8.14 of manual
for ultrasonic testing of Rails & Welds)
 (x) Systematic attention to cupped weld and replacement of corroded
/wheel burnt or worn out rails should be completed before onset of
winter.

48. PHOTOS OF WELD FAILURES

49. PHOTOS OF BAD
EXECUTION OF WELDS

50. THE END
 This presentation is prepared by LKO
division of NR on 25 Aug 2019 in the office of
SSE(P. Way)/Varanasi West for presenting in
IPWE seminar at LKO on 26 Aug 2019.