John Cookson - Institute of Railway Technology - Improving Weld Performance in Heavy Haul Railways

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

[email protected]

http://www.irt.monash.edu/

Institute of

Railway Technology


Heavy Haul Conference, Mackay August 2016

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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Railway Technology



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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Railway Technology



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– Previous AS1085.15 (now superseded)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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Railway Technology



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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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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Railway Technology



Aluminothermic welds

Key requirements

• Bond integrity

• Hardness distribution

• Running surface alignment

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Railway Technology



Aluminothermic welding

• Manually intensive manufacturing process

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Railway Technology



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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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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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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Railway Technology



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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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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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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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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Railway Technology



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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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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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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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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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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Railway Technology



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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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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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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Railway Technology



Summary

Current welding standard issues - AT welds• Training

• Accreditation of Training Organisations

• Training Programs

• Welder certification

• Auditing requirements

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Railway Technology



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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Railway Technology



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.

John Cookson - Institute of Railway Technology - Improving Weld Performance in Heavy Haul Railways

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