john cookson - institute of railway technology - improving weld performance in heavy haul railways
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Institute of
Railway Technology
Institute of Railway Technology
Department of Mechanical Engineering, Monash University, Australia
PO Box 31, Monash University, Victoria 3800, Australia
www.irt.monash.edu
Improving Weld Performance in Heavy Haul Railways
25 Aug 2016
Mackay Convention Centre
John Cookson
Team Leader, Rail Materials
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 2
Outline
• Influence of rail grade on welding requirements
• Key aspects of flashbutt and aluminothermic welding processes that impact on weld performance
• Standards and specifications; do they address the critical performance aspects
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 3
Rail welding
Setting the scene:– Rail quality has and continues to improve
• Increasing focus (and importance) attached to weld performance, as this may determine rail maintenance and replacement requirements, particularly in more demanding service environments
– Increasing diversity of rail grades in use.
– Increase in mobile flashbutt welds at the expense of AT welds
• Places more reliance on qualification requirements for this equipment
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 4
Rail welding standard
Australian Standard AS1085.20-2012
• Introduced in 2006: AS1085.20-2006
• Combination of:
– Previous AS1085.15 (now superseded)
- Aluminothermic welding
– New sections:
- Flashbutt welding
- Electric Arc Rail Head Repair welding
- Aluminothermic Head Repair welding (2012)
– Extensive revision of NDT inspection process & acceptance requirements (2012)
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 5
Rail grades
Wide diversity of rails entering Australian Market
• Previously – dominated by OneSteel in Whyalla
• International suppliers now have significant presence
• Steel originates from multiple mills, multiple grades from each mill
• Produced to European or American standards, rolled to AS1085.1 sizes
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 6
New rail grades – Welding issues• AT welding
– Does the AT welding process need to be fully/partially requalified for each new grade/size combination?
• FB welding
– Different alloying approaches and rail hardenability significantly complicates the welding and quenching requirements
– Rail grades with higher silicon content can be more difficult to weld
• Si levels alter kinetics of oxidation during flashing
• Can result in bond line discontinuities
– Current welding standard does not address rail grades other than those covered under AS1085.1
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 7
Aluminothermic welds
Key requirements
• Bond integrity
• Hardness distribution
• Running surface alignment
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 8
Aluminothermic welding
• Manually intensive manufacturing process
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 9
Aluminothermic welding
Weld quality control is critical• Many points in the process where
issues can and do arise
• Training quality and adhering to the process are critical
• Additional document or section in the standard required to mandate accreditation of trainers, training programs, welder certification, auditing, recording, etc.
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 10
Flashbutt welds
Key requirements • Bond integrity
• Hardness distribution
• Running surface alignment
Aspects not adequately covered
• Combination welds (different rail grades)
• Mobile vs stationary welders
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 11
Flashbutt weld bond integrity
Issues degrading performance• Insufficient maintenance leading to
degradation in weld quality
• Introduction of new rail grades that are inappropriately implemented
• Lack of clarity in the requirements for requalification following maintenance
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 12
Flashbutt weld bond integrity
Slow bend test• Bond integrity evaluated via the three
point bend test
• Simple, effective, conclusive
• Minimum load (stress) requirement
• Minimum deflection requirement to establish ductility
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 13
Slow Bend test requirements
• Comparison with International Standards
Standard Section Load (kN)
Outer fibrestress(MPa)
Deflection (mm)
AS1085.20 60kg/m 1330 900 20
AS1085.20 68kg/m 1670 900 12
EN 14587 60E1 grade R260& R320 fixed
60kg/m 1600 1068 20
EN 14587 60E1 grade R260& R320 mobile
60kg/m 1520 1015 20
AREMA High strength (4-point loading) 68kg/m(136lb/yd)
1745 860 19(0.75”)
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 14
Slow Bend tests – variation in results
68kg/m rail
• Compilation of past results for different rail grades– wide variation in data– should be possible to achieve at least 20mm
deflection in all rail welds with correct setup.
• Proposed combination of 2000kN and 16mm for high strength rail welds: – 3000µε plastic strain at base of foot,
– 1000µε plastic strain on top of foot
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 15
Slow bend tests
When are they required?• Australian Standard does not mandate frequency
of slow bend tests – many welds may be produced that have issues
Regular tests are advised• Ideally:
- One per shift for fixed welders
- One per 200 welds for mobile welders
- After any maintenance operation
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 16
Hardness requirements
Objective - Minimal deviation along running surface• Needs better definition of measurement zone (suggest ±10mm)
• Consider lower value for minimum hardness (-30HV rather than -20HV)
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 17
Hardness requirements
Width of softened zone
• Required in AS1085.20, but not in other standards
• Values may be 20mm, 30mm or 40mm.
• Contact length of wheel rail interface is ~20mm, so this width should be minimized.
200
250
300
350
400
-60 -40 -20 0 20 40 60
Har
dn
ess
(H
V1
0)
Distance from bond line (mm)
Head Hardened Rail
60kg
50kg
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 18
Quenching requirements
• Critical for OneSteel head hardened rail• Effectiveness varies significantly - design, configuration and application.
• Tremendous diversity of rigs - no guidance provided in AS 1085.20
– Role for supplementary document to provide information?
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 19
Hardness from mobile FB welders
Hardness difficult to achieve in OneSteel head hardened rail• Requirement for only -20HV below
parent rail hardness
• Consider reduction of minimum hardness to -30HV below unaffected parent rail for mobile FB welders
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 20
Combination welds
Welding different grades• Hardness mismatch means that neither FB
nor AT welds can meet the requirements
• Advise using cooling conditions to achieve intermediate hardness.
• Guidance required to formalize this approach.
200
250
300
350
400
-60 -40 -20 0 20 40 60
Har
dn
ess
(H
V1
0)
Distance from bond line (mm)
Standard Carbon/Head Hardened Rail
60kg
50kg
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 21
Alignment control
Alignment measurement• Currently measured by straight edge –
assumes peaking to a single point.
• More general case is that an offset is present, leading to impact loads.
– Mobile welders in particular
• Local slope limited to 7milliradians for AT1 welds – but unclear in current version of the standard.
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 22
Alignment issues
Significant impact loads due to offsets• Recent data – correlation between impact loads and weld gradient. • Better measurement and control - significant reduction in impact loads.
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Imp
act A
cce
lera
tio
n a
t 6
0km
/h (
g)
1 2 3 4 5 6 7 8 9 10 11 12
Maximum Gradient in Weld (mm/m)
Max weld gradient(mm/m)
7mm/m (or 7 milliradians)
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 23
Mobile FB welding issues
Substantial increase in FB mobile welders
• Mobile welders have less power available, which affects bond strength and hardness.
• Control of alignment is intrinsically more difficult.
• Maintenance intervals, operation, records, degradation significantly more challenging
• Separation or clarifying requirements for hardness, as well as re-qualification should be considered
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 24
Summary
Current welding standard issues - AT welds• Training
• Accreditation of Training Organisations
• Training Programs
• Welder certification
• Auditing requirements
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 25
Summary (continued)
Current welding standard issues - FB welds• Requalification requirements
• Definition of hardness measurement location
• Softened zone requirements
• Quenching rigs - guidelines
• Combination weld requirements
• Alignment measurement and control
• Requirements for mobile vs. fixed flashbutt welders
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Institute of
Railway Technology
Improving Weld Performance in Heavy Haul Railways
Heavy Haul Conference, Mackay August 2016Page 26
Where to from here?
• The process for modifying the AS 1085 suite of standards is in stasis at present – may be transferred to RISSB.
• “Buy in” from railways on the overall process, to provide momentum to the industry
• Preparation of proposed modifications to the AS 1085.20
• Training – set minimum requirements for accreditation of training organisations – either within standard or as a separate initiative.