Rail Choice, Modelling and Materials. Brian Whitney Principal - Track Engineer Network Rail 20 th November 2012

Transcription

1 Rail Choice, Modelling and Materials Brian Whitney Principal - Track Engineer Network Rail 20 th November

2 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 2

3 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 3

4 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 4

5 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 5

6 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 EQl Li Trailing Axle Leading Axle Cl Motion 6

7 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 7

8 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 8

9 Localised RCF at Weld Direction of Travel 9

10 RCF Management RCF Continues Represent A Major Risk To Rail Integrity If Not Adequately Managed RCF Continues To Be A Major Cause Of Premature Rail Replacement And A Major Drain On Maintenance Inspection Resources 10

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12 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 12

13 Low Rail RCF Damage Leading wheelset Trailing wheelset 13

14 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 Track-Ex WLRM Reports: Rail Damage info ACTRAFF Data: Fleet composition (vehicles) Vehicle Library: Vehicle Damage Potential GEOGIS Data: locations of S&C, etc + WRI Theory Exception Reports: Standards Compliance Track Plots: Rail Damage, Exceptions etc plots 14

15 TrackEx: Improved User Interface Design New interfaces are based upon a common format Easier For The User to Run Multiple Analysis 15

16 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 Now Provides Model for Premium Rail Analysis 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 16

17 Track-Ex Gap Loss Feature Life of a anti-rcf ground high rail is critical to rail life cycle costs & in future may be used to define grinding plans 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 17

18 Track-Ex: Route/Fleet Analysis The Route/Fleet Analysis can present results for the route as a whole 18

19 Effect of New Vehicles and Wheel Profiles Miles of track with RCF> woking-southampton woking-portsmouth waterloo-woking P8, 0CD, PYS= Year Old vehicles, P8 wheel profile (P1 wheel profiles=no RCF) Old Predicts vehicles, 4 track P8 wheel miles profile heavy/severe (P1 wheel profiles=no RCF in 10 RCF) years Predicts 4 track miles of heavy/severe RCF in 10 years 19

20 Effect of New Vehicles and Wheel Profiles Miles of track with RCF> woking-southampton woking-portsmouth waterloo-woking P8, 0CD, PYS= Year Desiro vehicles, new P8 wheel profile Predicts 27 track miles of heavy/severe RCF in 10 years 20

21 Rail Grinding The Target Ground profile: Provides relief in gauge shoulder area on the high rail of curves 0.6mm 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 21

22 Ground Profiles Contact Position New P8 on new rail profile straight track Contact Position New P8 on new rail profile curved track Contact Positions New P8 on ground rail profile with shoulder relief curved track 22

23 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 23

24 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. 24

25 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 25

26 RCF Resistance and Rail Wear RCF Resistance Rail Wear Rate Grade 260 HP MHH Grade 260 HP MHH Time for RCF to Appear Wear Rate Rail Steel Rail Steel 26

27 Premium rail life cycle costs Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 1 Grade 260 rail with no grinding or lubrication 350, ,000 Life Cycle Cost 250, , , ,000 50, Year Grade 260 No Grinding or Lubrication 27

28 Premium rail life cycle costs 350, ,000 Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 2 Grade 260 rail with grinding and lubrication Life Cycle Cost 250, , , ,000 50, Year Grade 260 No Grinding or Lubrication Grade 260 Grinding and Lubrication 28

29 Premium rail life cycle costs Typical 1100m Radius Curve (500m long, 25MGTPA) LCC plot 3 Premium rail with grinding and lubrication 350, ,000 Life Cycle Cost 250, , , ,000 50, Year Grade 260 No Grinding or Lubrication Premium Rail Grinding and Lubrication Grade 260 Grinding and Lubrication 29

30 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 450, , , ,000 LCC 250, , , ,000 50, Years HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication 30

31 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 450, , , ,000 LCC 250, , , ,000 50, Years HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication MHH Rail Grinding and Lubrication 31

32 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 1,600,000 1,400,000 1,200,000 1,000,000 LCC 800, , , , Years HP Rail Grinding and Lubrication Grade 260 Grinding and Lubrication MHH Rail Grinding and Lubrication 32

33 Hett Mill Up Fast Rail management costs 260 vs HP Rail Management Cost for Hett Mill Up Fast Cost Year 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 33

34 Thank You Brian Whitney Principal - Track Engineer Network Rail Date