Study of Rail Structure: Risk Analysis and Failure Mode

Study of Rail Structure happen Analysis and Failure ModeStudy of Rail StructureRisk Analysis and Failure Mode AvoidanceIn this case study, a brief overview of prepareroad track structure is discussed. Defects related to caterpillar track failure are considered infixed to frame out the correct maintenance strategy. As it is closely associated with safety of passenger and cargo transportation, hence it retains high venture in ground of tender-hearted lives and personify of resources. There will always be some risk associated with collisions and de vilifyments except it can be descendd by eradication of the root causes. delineation and amendment of train defects are major issues for all complain companies around the world.There are challenges to the infrastructure maintenance individuals to perform efficacious inspection and cost efficacious rectification decisions. If addressed properly these can scale down capability risk of civilize breaks and de educatements.Risk assessment and Failure mode avoidance has become a vital constraint for the organisations to decide a cost effective and improved solution that could meet the financial constraints regarding inspection, renewal and replacement of inveighs and vagabonds. This study aims to reduce cost and risks related to rail operation by effective approaches. The issues and challenges related to rail maintenance are outlined. The maintenance strategy followed by well-nigh railway companies is also defined.Large Railways infrastructures are the prime manner of transportation in several countries. Improved and better safety measurements are continuously presented but dumb could not be considered as incidents proof. There will always be some risk related with derailments and other occurrences such as major intermission to services, which can furthered be minimised by detailed examination of the root causes. Some of the causes require improvement in skill and efficiency, for example human error, a nd some may be improved by optimization of inspection regularity. Therefore, a appropriate thorough study of the defects which develop both on the rolling stock and rail infrastructure is vital to frame out the correct maintenance approach. European Union spends around 2 billion every year for maintenance and repairing of distressed rails (European Commission Cordis, 2017). It is understood that the consequential cost collect to derailment decreases with rise in inspection, lubrication and grinding charges. Risk in railways could be expressed in terms of cost, loss of human lives, infrastructure unavailability, traffic delay and environmental impact which may be cause referable to derailment of a train carrying hazardous sensible.In this report, diametrical kinds of rail defects and maintenance procedures followed aredescribed. Different risk assessment and failure mode avoidance methods and tools have been discussed briefly in this report. Some of the issues and challenges related to railmaintenance are also addressed with an aim to reduce the total cost and risks associated with rail operations.Rails are longitudinal make members that accommodate wheel around loads and distribute these loads over the standoffs or supports, guiding the train wheels evenly and continuously. It is one of the most important components of the track structure. Usually a insipid bottom railis used in conventional railway track, which can be separated into 3 parts rail engineer, rail weband rail foot. Many standards are used for rail pens. (Kumar, 2007) issue 1 shows the 2 parkland rail profiles. write in code 1 Flat bottom and Bullhead rail profilesThe rails must possess sufficient insensibility so that they can act as beams and transfer the concentrated wheel loads to the spaced sleeper supports without excessive deflection between supports. (Ernest and lav, 1994)Due to economic pressure, there is a world-wide trend to increase axle loads, traffic densityand speed to reduce the operating cost and increase the efficiency of railways. Axle loadsaround the world have increase in general from 22.5 to 32.5 Tonnes in last ten years (Allen, 1999). This has led to increased rate of defect formation in rails. Some of the common defects are described in the following sections.4.1. ShellingShelling is a defect caused by loss of material initiated by subsurface fatigue. Shelling normally takes place at the gauge corner of high rails in curves. An elliptical dress down like crack propagates in the subsurface parallel to the rail surface. When these cracks emerge on the surface, they cause the metal to come out from the crack area. It is generally eliminated by grinding. (Kumar, 2007)Figure 2 Shelling caused by Head Checks4.2. Head ChecksIn the crown area, the contact stresses are generally low as it has greater profile radius incomparison to the gauge side of rail. However, high contact stresses are produced on the high rails gauge corner, which usuall y has curve radius from 1000 to 1500 m. Headchecks are known to occur in tighter ((IHHA, 2001).If head checks are not statementled, they can cause a rail break. Grinding is the most common practice to remove head checks. Severe head checks need rail section replacement.4.3. SquatsUnlike shelling, squats appear in crown area of uncoiled rail sections. They are surfaceinitiated defects formed by RCF. A squat is formed by two cracks, a leading crack and atrailing crack. Both these cracks propagate in opposite direction. These defects could be prevented by grinding. (Kumar, 2007)4.4. SpallingSpalling occurs, when the surface initiated crack development path is intersected by other similar shallow cracks on the rail head area, a shallow chip of rail material falls out. Spalling is more common in cold climates as rail stiffness increases.Figure 3 Gauge Corner Spalling in rails 4.5. Tache OvaleTache Ovale is a subsurface defect formed around 10-15 mm below the rail head surface (see Figu re 4). This is caused by hydrogen accumulation during manufacturing of rail or when poor welding is done in rails. Thermal and residual stresses also summate to form this defect.Figure 4 Tache Ovale 4.6. Plastic Flow and Tongue LippingPlastic flow occurs in rail head area, the depth of which may be up to 15 mm. Plastic flowoccurs on the field side of the low rail due to overloading. Tongue lipping is also a form of plastic deformation, but it is initiated by surface cracks. These cracks partially separate a layer of material from the bulk of rail. (IHHA, 2001)4.7. Bolt Hole CrackBolt holes appear in the rail web often starting from the fastening point of fishplates. Butthese become weak points to resist crack initiation. These cracks have a very high capability to cause rail break and needs urgent replacement.4.8. Longitudinal Vertical CrackThis is a manufacturing defect, which usually appears in the rail web and may transmit in railhead also. If this crack is intersected by some other crack, it may lead to an early rail suspension. Odds of sudden fracture due to this become predominant in cold climate.Figure 5 Longitudinal vertical crack 4.9. thwartwise CrackTransverse crack is mostly developed in the cross-sectional area of wrong weld joints. Awelding defect may be due to variation in weld material or rail manufacturing defect. Figure 6 shows a Transverse crack develops from the centre of the rail head or the rail foot. Use of clean steel and deeper hardening of rail head may avoid its formation. (Kumar, 2007)Figure 6 Transverse crack 4.10. BucklingLateral buckling in rails is a very common defect in which the rail bulges out on its either sidedue to expansion. As the temperature rises, longitudinal expansion in rail takes place.4.11. CorrugationCorrugation is a rail flaw consisting of the wave-like go intoing of the rail tread visualized aspeaks and valleys, in other words, it is a periodic irregularity of the rail surface (IHHA, 2001),see Figure 7.F igure 7 Corrugation in railsRail corrugations are the result of a damage mechanism, such as wear etc. Rail corrugations do not pose risk of immediate derailment, but they may be responsible for loosening of rail fastenings, ballast deterioration, increase in noise and thrill level leading to passenger discomfort, etc.Two main types of corrugations which generally occur in rails areShort stagger corrugationsLong pitch corrugationTables below show the percentage and type of defect detection by different rail infrastructurecompanies.RailwayFirstSecondThird after partRail track (1999/2000)Squats 21.7%Vertical/transverse 20.1%Horizontal/longitudinal 12.5%Bolt holes 9.6%SNCF (1999)Squats 23.4%Internal fatigue 11.5%Shells 8.4%Thermite welds 4.7%HSPC (1999)Thermite welds 31.5% roll out burns 17.2%Horizontal split webs 13.3%Bolt holes 11.3%NS (1997)Insulated Joints 59.4%Transverse defects 18%Thermite welds 15%Fatigue Failure5.2%DB (1996)Thermite welds 29%Sudden fracture 18%Fatigue Failure 16%Electric bonds4.0 %Banverket(1998)Transverse fracture 55.1%Welded joint 32.7%Horizontal defect 6.1%Vertical split2.0%HH1 (1999)Vertical split heads 34.7%Thermite welds 20.3%Detail fractures 13.1%Bolt holes 12.2%HH2 (1999)Transverse defects 23.6%Thermite welds 15.5%Wheel burns 13.2%Shells 9.6%Table 1 Causes of defective rails (Source Kumar, 2007)Rail breaks and derailments can cost the rail players in terms of loss of revenue, property, environmental damage or even loss of life. Estimation of these costs and analysis of risks are important in deciding effective maintenance strategies. In simple terms, risk can be defined as the find out or probability of loss, damage or injury. (Reddy, 2004)5.1. Failure Mode and Effects Analysis (FMEA)FMEA is a step-by-step procedure for systematic evaluation of the severity of potential failure modes in a system. This process was originally developed in the 1960s, to analyse the safety of aircrafts, but has been since applied to several other fi elds, including nuclear condition plants and the military. (Villemeur, 1992-A)Figure 8 Schematic representation of the FMEA. (Source Villemeur, 1992-A).5.2. Risk Priority Number (RPN)Risk priority number (RPN) is a methodology for analysing the risk associated with potentialproblems identify during (FMEA) (for details refer Reliasoft, 2005).Assigning RPN requires the analysis team to rate each potential problem per three rating scalesSeverityOccurrenceDetectionafter the ratings, have been assigned the RPN for each issue is calculated as mentioned below,RPN = Severity x Occurrence x DetectionRail maintenance issues can be broadly classified intoInspection issuesIssues related to rail wear, RCF and rail weldingRectification and replacement issues6.1. Rail Inspection IssuesThe effectiveness of rail inspection depends on the efficiency and accuracy of the inspectingequipment. It also depends on the skill and experience of inspectors. Error in inspection is an important issue and its re duction is a big challenge. This principally depends on the technological limitations of the inspection equipment and the skill level of the rail inspectors.Figure 9 Rail inspection issues (Source Kumar, 2007)6.2. Issues related to Rail Wear, RCF and Rail WeldingFigure 11 outlines the rail maintenance issues. The following sections briefly describe someof these issues.Figure 10 Rail maintenance issues (Source Kumar, 2007)6.2.1. Rail Wear IssuesWear occurs due to interaction of rail and wheel. It includes mild and severe wear. Mild wear takes place slowly but severe wear is often much faster. Severe wear is predominant in curves and occurs dry conditions. Lubrication techniques are used to prevent such wears.Four commonly used techniques which are followed for rail-wheel lubrication areTop of rail lubricatorsWheel flange lubricatorsWayside lubricatorsOn board lubricators6.2.2. Rolling Contact Fatigue (RCF) IssuesIn the late 1990s RCF accounted for about 60% of defects found by eins teinium Japan Railways, while in France (SNCF) and UK (Railtrack) the calculates were about 25% and 15%,respectively. RCF is a major future concern as business demands for higher(prenominal) speed higher axle loads, higher traffic density and higher tractive forces increase (see Cannon et al, 2003).Rail grinding removes surface metal from the rail head. It is done mainly with intensions to control RCF defects and rail wear. Rail grinding became increasingly recognized for controlling RCF defects from 1980 onwards, prior to that it was mainly focused on corrugation removal.6.2.3. Rail Welding IssuesSmall imperfection in welds can cause cracks to initiate. A defect free weld requires skilledworkforce, better weld material along with improved welding techniques and equipment.6.3. Other Issues bear upon Rail Wear, RCF and Rail WeldingRisk and cost are analysed by rail infrastructure operators in maintenance decisions. It covers rail lubrication, rail grinding and rail weld.Other impor tant issues areRail materialRail traffic density and axle loadTrack geometryIn Conclusion, first a brief overview of rail structure is discussed. Then, diverse range of rail defects and degradation processes have been studied. From the literature analyses done, it is interpreted that there is a need for better ways to monitor and divine rail defects over a period based on operational conditions and maintenance tactics. A good knowledge of risk along with an idea of the methods used for risk analysis is also required. Hence, before improvement of any model or any empirical relationship associated with risk and failure, there should first be a familiarity with risk management tools and failure mode avoidance. This study focuses on some such tools.Also, the issues and challenges related to rail maintenance are discoursed. The aim is to reduce risks related to rail operation that leads to failure mode, by effective decisions associated to rail inspection, grinding, rectifications lubri cations, and rail replacements. Some of the challenges in this area include development of cost effective maintenance decisions, reliability and availability of logistics support, which include availability of capable equipment, skilled personnel and availability of rail track.8.1. ReferencesAllen, R., (1999) Finding best practice at the wheel/rail interface, International RailwayJournal, flock 6, pp. 48-50.European Commission Cordis (2017) AutoScan Rail inspection. useable from http//cordis.europa.eu/project/rcn/203338_en.html sighted February 2017Cannon, D. F., Edel, K.O., Grassie, S. L. and Sawley, K. (2003) Rail defects an overview,Fatigue Fracture of Engineering Materials Structures, Volume 26, October 2003, pp.865-886.Ernest, T. S. and John, M. W. (1994) Track Geometry and Substructure Management,Thomas Telfold.IHHA (2001) Guidelines to best practices for heavy haul railway operations wheel and railinterface issues, International Heavy Haul Association, whitethorn 2001, V irginia, USA.KUMAR, S. (2007). Study of Rail Breaks Associated Risks and Maintenance Strategies. Lulea Railway Research Center (JVTC)MIL-STD-1629A, (1980) Military Standard Procedures for Performing a Failure Mode,Effects and Criticality Analysis, Department of Defence, USA. Available from http//www.uscg.mil/hq/g-m/risk/e-guidelines/RBDM/html/vol4/Volume4/Toolspec_Rec/FMEA/MIL-STD-1629A.pdf sighted February 2017Reddy, V. (2004) Modelling and Analysis of Rail Grinding Lubrication Strategies forControlling Rolling Contact Fatigue (RCF) and Rail Wear, Master Thesis, QueenslandUniversity of Technology, Brisbane, Australia.Reliasoft (2005) Examining risk priority numbers in FEMA, Reliability Edge, volume 4,issue1. Available from http//www.reliasoft.com/newsletter/2q2003/rpns.htm sighted February 2017VILLEMEUR, Alain (1992-A, 1992-B). Reliability, Availability, Maintainability and Safety Assessment, A Vol. 1 Methods and Technique. B Vol.2 Assessment, Hardware, software product and Human Factors John Wiley Sons.8.2. FiguresFigure 1 https//upload.wikimedia.org/wikipedia/commons/thumb/4/4b/Rail_profile.svg/800px-Rail_profile.svg.png?1487817217791Figure 2 http//www.ndt.net/article/v07n06/thomas/fig3.jpgFigure 3 http//www.railwayexpertwitness.com/images/inspect9-300.jpgFigure 4 https//www.researchgate.net/publication/229632336/figure/fig8/ASemailprotected/Figure-1-Tache-ovale-or-kidney-rail-failure.pngFigure 5 http//www.ndt.net/article/0698/schub/fig1.gifFigure 6 http//mikes.railhistory.railfan.net/imfile/09192.jpgFigure 7 http//railmeasurement.com/wp-content/uploads/2015/04/corrugation-track1.jpgFigure 8VILLEMEUR, Alain (1992-A, 1992-B). Reliability, Availability, Maintainability and Safety Assessment, A Vol. 1 Methods and Technique. B Vol.2 Assessment, Hardware, Software and Human Factors John Wiley Sons.Figure 9 and 10KUMAR, S. (2007). Study of Rail Breaks Associated Risks and Maintenance Strategies. Lulea Railway Research Center (JVTC)