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20th November 2012

Rail Choice, Modelling and Materials Brian Whitney Principal - Track Engineer Network Rail

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Rail Loading - Surface Damage •  This type of damage accounts for the majority of defects we see in track and is a result of

cumulative damage from the repeated passage of a wheel over a rail leading to RCF, squats, wheelburns, corrugation, rail deformation etc.

•  The main factors influencing this type of damage are

–  Contact stresses primarily influenced by axle weight, wheel and rail profile

–  Longitudinal creep and lateral forces from curving, traction and braking

–  Vehicle suspension design particularly primary yaw stiffness and bogie unsprung mass

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Rail Forces – Surface Damage

•  In many cases these excessive loads may not instantly break the rail but can initiate small fatigue cracks that subsequently propagate under normal loading

•  Rail life is dependant on the forces it is subjected to and the length of time it is subjected to them

•  Work is being carried out to better the identify precursors to defective and broken rails to prevent premature degradation and failure, better management of geometry such as dipped joints to reduce the forces acting on the track system

•  Measurement and management of abrupt changes in track stiffness which lead to higher forces on the track system

•  Fixing faults quickly and early to greatly reduce the cumulative damage and increase component life

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Reducing Surface Damage •  Use of modelling tools to analyse vehicle track interaction to better

prioritise remedial action to those features giving rise to most damage

•  Development of harder rail steels to combat low rail plastic flow and preserve the high rail profile longer – Tata Scunthorpe HP premium grades now being installed in track and showing significant performance benefits

•  Top of Rail Friction Modification to control friction levels on the running surface particularly in tight radius curves

•  Modified wheel profiles (P12) and vehicle suspension characteristics (Hall Dynamic Bush) to reduce RCF now both under trial and showing significant benefits

•  Improved grinding planning to deliver timetabled C21 grinders with modified frequencies and patterns

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Prediction and Prevention •  Early identification of RCF and monitoring of initiation and growth using

surface crack detection techniques

•  Use of modelling to improve management of the wheel rail interface

•  Better understanding to identify key locations where the use of premium rail steels is of greatest benefit

•  Avoidance of immediate action defects and the need for immediate speed restrictions

•  Optimisation of grinding plans to control initiation and early growth

•  Understand RCF deterioration rates to plan re-railing at the optimum time

•  Link RCF damage with geometry faults to prevent initiation by correcting underlying faults

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Typical Bogie Forces & RCF Understanding and Modelling • The leading axle tends to exhibit over shifting and positive angle

of attack while the trailing axle typically shifts to the equilibrium line and remains aligned with the track centre line

•  Leading axle forces usually exceed those of the trailing axle

Lo

Li Cl

EQl

Leading Axle Trailing Axle

Motion

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RCF Forces

• The dominance of longitudinal forces explains why so much of the RCF is in curves where we are close to flange contact and small changes in position of the wheelset has a dramatic effect on the contact position and rolling radius difference

• This also accounts for the angle of cracking on the surface and the inclination that the crack grows into the rail

•  When RCF is found in straight track, it is usually associated with a track geometry feature that causes a significant change in the contact position and induces high longitudinal and lateral forces

• Track-Ex developed to enable RCF damage and wear to be assessed and modelled for actual routes, real vehicles and a range of track conditions

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From Theory to Observation:

The RCF Crack angle

•  Cracks generally grow perpendicular to the resultant force and the angle of the cracks as predicted in analysis matches that observed in the field

RCF Forces

Direction of Travel

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Localised RCF at Weld

Direction of Travel

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RCF Management

RCF Continues To Be A Major Cause Of Premature Rail Replacement And A Major

Drain On Maintenance Inspection Resources

RCF Continues Represent A Major Risk To Rail Integrity If

Not Adequately Managed

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Low Rail Damage

• The forces shown on the earlier slide also give rise to low rail damage

• This frequently is in the form of low rail corrugation, particularly in tight radius curves less than 400m, and is caused by the repeated slip of the wheels causing localised wear which becomes worn into the surface of the rail leading to increased dynamic forces and in turn plastic flow, longitudinal cracking towards the field side of the rail and lipping. In extreme cases this can lead to gross plastic flow and partial collapse of the rail head

•  In other instances, 400 to 800m, the surface forces cause shallow surface cracking leading to light surface spalling

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Leading wheelset

Trailing wheelset

Leading wheelset

Trailing wheelset

Low Rail RCF Damage

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Track-Ex: Theory Into Practice • Track-Ex uses several sources of data as inputs and essentially “adds value” to the data by using the theory of the Wheel/Rail Interface to create new information for industry engineers

Track Geometry Data: curvature, gauge, etc

ACTRAFF Data: Fleet composition (vehicles)

Vehicle Library: Vehicle Damage Potential

GEOGIS Data: locations of S&C, etc

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WLRM Reports: Rail Damage info

Exception Reports: Standards Compliance

Track Plots: Rail Damage, Exceptions etc plots

Track-Ex

WRI Theory

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TrackEx: Improved User Interface Design

• New interfaces are based upon a common format

• Easier For The User to Run Multiple Analysis

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Track-Ex: Theory WLRM

•  TGamma increases as the contact patch moves from top-of-rail to the gauge face for the high rail leading axle

–  this occurs in curves & in response to lateral track perturbations

– Tread TGamma above 175 is rare

•  The WLRM drop in RCF is due to the onset of wear that removes metal even as the cracks grow. Eventually wear dominates

•  Therefore RCF damage is most likely on the rail shoulder for Grade 260 and the gauge corner for Grade 400 rail

Now Provides Model for Premium Rail Analysis

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Track-Ex Gap Loss Feature

• NWR has developed a Gap-Loss index that estimates the reduction in the anti-RCF gap as a function TGamma

Ground Rail Gap

• This should enable the benefits of grinding to be better analysed. Wear rates can be assessed and grinding plans optimised in conjunction with the use of premium rail steels and revised wheel profiles

•  Life of a anti-RCF ground high rail is critical to rail life cycle costs & in future may be used to define grinding plans

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Track-Ex: Route/Fleet Analysis • The Route/Fleet Analysis can present results for the route as a

whole

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Effect of New Vehicles and Wheel Profiles

0

5

10

15

20

25

30

0 2 4 6 8 10

Year

Mile

s of

trac

k w

ith R

CF>1

5 woking-southamptonwoking-portsmouthwaterloo-woking

P8, 0CD, PYS=8

Old vehicles, P8 wheel profile (P1 wheel profiles=no RCF)

Predicts 4 track miles of heavy/severe RCF in 10 years Old vehicles, P8 wheel profile (P1 wheel profiles=no RCF)

Predicts 4 track miles of heavy/severe RCF in 10 years

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Effect of New Vehicles and Wheel Profiles

0

5

10

15

20

25

30

0 2 4 6 8 10

Year

Mile

s of

trac

k w

ith R

CF>1

5

woking-southamptonwoking-portsmouthwaterloo-woking

P8, 0CD, PYS=24

Desiro vehicles, new P8 wheel profile

Predicts 27 track miles of heavy/severe RCF in 10 years

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Rail Grinding

0.6mm •  The Target Ground profile:

– Provides relief in gauge shoulder area on the high rail of curves

– prevents wheel/rail contact in this area and reduces conicity

– Prevents generation of forces sufficient to initiate RCF

– Can increase gauge face contact

– Can` increases the need for gauge face lubrication

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Ground Profiles

New P8 on new rail profile – straight

track

New P8 on ground rail profile with

shoulder relief – curved track

New P8 on new rail profile – curved

track

Contact Position

Contact Positions

Contact Position

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HP Steel Development – The Basis

•  Virtually all rail steels in use today have a pearlitic microstructure comprising a lamellar of “soft ferrite” and “hard cementite”

•  Pearlite is a 3-dimensional entity and the wheel encounters both the ferrite & cementite laths at a wide range of orientations

•  How does this composite microstructure react to ratchetting or the initiation of RCF

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HP Steel Development – The Basis

•  RCF Cracks – a high resolution 3D view reveals formation of a ledge from the ratchetting action on the surface of the rail

•  The widely different properties of the ferrite and cementite and the wide range of orientations at the running surface must react differently to ratchetting action

•  Basis of HP steel development:

– Not essential to increase hardness of steel through alloying and/or heat treatment

–  Instead, increase volume fraction of cementite and increase the strength of ferrite to make ratchetting more difficult.

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The Goals

• Maximise average rail life

– CEN60 rail on concrete >1200 EMGT

– CEN56 (113A) on concrete > 750 EMGT

• Grinding typically £1 per m per cycle

•  Lubrication, typical curved site £2 per m per year

• HP rail steel typically an extra 15% increase on std rail costs

• At approximately £200 per metre to replace rail there is a huge benefit in avoiding premature rail replacement and maximising rail life

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Rail Wear Rate

Gra

de 2

60 HP

MH

H

Rail Steel

Wea

r R

ate

RCF Resistance

Gra

de 2

60 HP

MH

H

Rail Steel

Tim

e fo

r R

CF

to A

pp

ear

RCF Resistance and Rail Wear

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Premium rail – life cycle costs

£0

£50,000

£100,000

£150,000

£200,000

£250,000

£300,000

£350,000

0 2 4 6 8 10Year

Life

Cyc

le C

ost

Grade 260 No Grinding or Lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 1 – Grade 260 rail with no grinding or lubrication

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Premium rail – life cycle costs

£0

£50,000

£100,000

£150,000

£200,000

£250,000

£300,000

£350,000

0 2 4 6 8 10

Year

Life

Cyc

le C

ost

Grade 260 No Grinding or Lubrication Grade 260 Grinding and Lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 2 – Grade 260 rail with grinding and lubrication

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Premium rail – life cycle costs

£0

£50,000

£100,000

£150,000

£200,000

£250,000

£300,000

£350,000

0 2 4 6 8 10

Year

Life

Cyc

le C

ost

Grade 260 No Grinding or Lubrication Grade 260 Grinding and LubricationPremium Rail Grinding and Lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 3 – Premium rail with grinding and lubrication

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Life Cycle Costs Grade 260 vs HP, grinding & lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 1 – Grade 260 vs HP rail, grinding & lubrication, 10 Year costs

£0

£50,000

£100,000

£150,000

£200,000

£250,000

£300,000

£350,000

£400,000

£450,000

0 1 2 3 4 5 6 7 8 9 10

Years

LCC

HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication

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Life Cycle Costs Grade 260 vs HP vs MHH, grinding & lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 1 – Grade 260 vs HP vs MHH rail, grinding & lubrication, 10 Year costs

£0

£50,000

£100,000

£150,000

£200,000

£250,000

£300,000

£350,000

£400,000

£450,000

0 1 2 3 4 5 6 7 8 9 10

Years

LCC

HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication MHH Rail Grinding and Lubrication

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Life Cycle Costs Grade 260 vs HP vs MHH, grinding & lubrication

Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 1 – Grade 260 vs HP vs MHH rail, grinding & lubrication, 40 Year costs

£0

£200,000

£400,000

£600,000

£800,000

£1,000,000

£1,200,000

£1,400,000

£1,600,000

0 5 10 15 20 25 30 35 40

Years

LCC

HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication MHH Rail Grinding and Lubrication

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Hett Mill Up Fast Rail management costs 260 vs HP

Rail Management Cost for Hett Mill Up Fast

100000

150000

200000

250000

1 2 3 4 5 6

Year

Cos

t

Grade 260 Rail HP rail

•  Historical grade 260 costs vs. forecast HP rail costs •  HP rail expected to give a cost benefit from early year 4 due to lower grinding and

inspection costs

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Thank You

Brian Whitney Principal - Track Engineer Network Rail