INTRO: Developed by the Wayside Monitoring Alliance, the Supersite condition monitoring station is designed to provide comprehensive data on passing wagons, using root cause analysis and predictive maintenance to prevent small defects leading to major problems
BYLINE: Trevor Bladon PhD
Wayside Monitoring Alliance
SIGNIFICANT progress has been made in recent years to reduce the stress state of railways, helping to lower the forces exerted on track and infrastructure. Attention is now turning from the permanent way towards rolling stock, a field where research has so far been slower to develop.
In 2002 four suppliers of field-proven wayside monitoring equipment joined forces to form the Wayside Monitoring Alliance (right). This has led to the development of Supersite, a comprehensive multi-sensor wayside monitoring system offering far more than the reactive ’go/no-go’ warnings of traditional wagon monitoring devices. Alliance members have had their products co-located in different combinations at various locations in Australia, Europe and the USA since 2001, and sharing findings has helped to improve the accuracy of conclusions drawn.
Until now typical trackside sensors have been neither sensitive nor specific enough for predictive monitoring, instead triggering alarms at a threshold where the wagon is likely to inflict immediate damage to the infrastructure, even though much damage will already have been initiated by then. However, modern detectors are able to detect damage to individual vehicles or components as it first emerges, allowing trends to be identified and maintenance carried out to prevent further damage.
Supersite offers a comprehensive validation of wagon condition (Fig 1), from the wheel-rail contact surface to wheel profiles, dynamic behaviour of axles, bearing health, bogie geometry, wagon stability and train handling. It is designed to be adaptable and can be further developed to incorporate the industry’s future needs.
Identifying the bad actors
The Wayside Monitoring Alliance believes the rail industry needs to review both its existing standards and monitoring methods. North American operators feel bound to abide by legal minimum standards such as the Association of American Railroads interchange rules, which have yet to be brought into line with the capabilities of current technology.
Effective performance management requires accurate assessment of vehicle performance trends and real-time reporting to the appropriate departments, which need raw data, not just symptomatic, normalised or estimated values. Supersite’s data management is accomplished by the Wayside Management System, which collates the outputs of a diverse range of sensors into a database, along with vehicle identities collected from Automatic Equipment Identification radio-frequency tags where available. Trends and root data are available to users, with security and access rights controlled by the WMS owner. Customised data feeds a link to the operator’s IT department, and a full analysis suite allows real-time monitoring of vehicle condition, bogie and train dynamics.
The combined performance parameters help to identify the ’bad actors’ which generate high stresses at the wheel-rail interface.
Three examples illustrate how a damaged component can initiate new and accelerating damage in healthy components.
1. Defect interaction. Although bearing faults often arise with no measured wheel defects or aberrant geometry, on numerous occasions other damage will have preceded the bearing defects. A Teknis wheel condition monitor at one site recorded an abnormal wheel impact on April 5 2003 (Fig 2a), and the impact grew rapidly though July, with some speed dependence as it matured (the jagged trace in Fig 2c) to a peak impact of 350 kN.
Significantly, the Vipac RailBAM began to measure excessive looseness and fretting in the bearing in mid-May (Fig 2b), in addition to wheel flats and noisy wheels. Bearing looseness and fretting readings continued at a high level for 10 weeks before the vehicle owner heeded the warnings and removed the wagon from service for repair (Fig 2d). It seems plausible that the bearing was damaged by high impact forces transmitted through the defective wheel.
2. Defect propagation. Once a wheel defect occurs, the severity of impacts will increase over time, and this often leads to collateral damage. In late September 2002 a wheel on one axle was damaged, and we began to plot its impacts (Fig 3). The second wheel on the axle was soon damaged, and by early January the wheels on the adjacent axle began to show small impacts. The damage continued to worsen on both axles.
3. Bogie Geometry. The Truck/Bogie Optical Geometry Inspection station from Wayside Inspection Devices optically measures the angle of attack of the axles, and their orientation relative to the centreline of tangent track. Bogies with geometry faults can cause expensive secondary damage, and Fig 4 shows the results of a bogie running uncorrected for an extended time with a large tracking error (>21mm) and a small inter-axle misalignment. Wheel wear developed asymmetrically (w, Fig 4), and the flanges were damaged.
These examples clearly reinforce the need to review current outdated practices and standards. The AAR interchange rules require wheels to be removed from service once they reach an impact level of 400 kN, but the impacts in the first two examples never reached this high threshold. The wagon remained in service, but experience shows that impacts of only 200 kN can initiate widespread damage to wheels on the same and adjacent axles.
In some instances there are no industry standards to deal with the data from predictive monitors. A bogie with impaired steering was identified by TBOGI, but not repaired. The ongoing residual rotation on straight track was as small as 2milliradians, but still contributed to a derailment on a curve, causing extensive damage to the track and rolling stock.
Our examples illustrate the seeding of damage which occurs while we wait for today’s alarm thresholds to be reached.
But timing the replacement or repair of failing components is a balancing act. Is there residual value in a damaged component which is repaired before it reaches the accepted high threshold or triggers a hotbox alarm? However, operators must consider the effects and expense of leaving worn wheels or poorly tracking bogies in service, where they will exert cumulative forces on the rails and sleepers.
Our examples hint at the value and cost-effectiveness of predictive condition monitoring, and show that the practice of leaving components in service until failure is imminent or actual must be reviewed in the light of monitoring data.
As another example graphically demonstrating the value of early intervention, Fig 5 shows as a red trace a minor wheel defect which appeared in early May 2003 and developed into a speed dependent major defect (Fig 5b) over five months. Within four weeks of wheel defect initiation, looseness and fretting appeared in the bearing at a high level (Fig 5c), and continued for 14 weeks, with bearing and wheel continuing to deteriorate.
Wanting to obtain residual value from the failing components, the operator did not heed our warnings until the defective truck caused a derailment in September (Fig 5d). Subsequent analysis by the Alliance and discussion with the vehicle owner determined that the incident had begun in May with a small wheelskid caused by improper loading, and this seemingly minor event had catastrophic effects five months later. After a series of derailments, the operator changed its procedure for handling data from the Alliance’s wayside detectors.
As the Alliance developed the sensors and data management systems for the Supersite we anticipated the need properly to assess the condition of rolling stock. Our members have many years’ experience of monitoring traffic around the world, and this has been pooled to create a model of the damage that can follow a defect (Fig 1).
The model includes damage to wheel bearings, bogie geometry and wheel surfaces, profile and wear (blue hexagons). Many of the damage initiators are listed around the outside, with arrows to the parameter in question. Arrows from the parameters indicate the consequences of damage.
The model is in the form of a cycle because our data strongly indicate that damage will form a positive feedback loop if not repaired. This is emphasised by the trends shown by the blue arrows between the hexagons. Arrows at the centre of the cycle indicate that the longer out-of-specification components are left in service, the deeper and more widespread the damage will be, leading to increased repair and fuel costs, expensive remedial work to the track, increased risk and more severe and widespread faults in the vehicle fleet.
A final example illustrates how the data can be utilised to determine root causes of problems. RailBAM measured the wheel noise emitted from one bogie because of a flanging wheel with poor geometry. The noise grew steadily from January to July. Looseness and fretting in the bearing had reached a high level by early March, coinciding with the appearance of small wheel flats. Bearing defects began to appear and looseness and fretting values grew. The small wheel flats grew and impacts ultimately reached 300 kN by July, when wheel and bearing defects exceeded the maximum permitted levels. This wagon was then repaired, and all detector levels returned to normal. Significantly, the whole process repeated itself within three months.
Subsequent investigation after a second repair cycle showed that the wagon in question had been involved in an earlier derailment which had bent the bogie frame. By using multiple detectors and identifying trends, it became possible to decipher more clues about the root causes of damage, and expose the false economy of repetitive repairs.
TABLE: Wayside Monitoring Alliance
Teknis Electronics Pty Ltd wheel condition, vehicle dynamics, data management
Vipac Engineers and Scientists Ltd bearing acoustic monitoring
Wayside Inspection Devices Inc optical bogie geometry, vehicle stability
ImageMap Inc optical wheel profile measurement
TABLE: Table I: Features of the Alliance Supersite
Wheel/rail contact; impact (independent of mass); defect classification; wheel profile;diameter, flange, rim etc; built-up, grooved or hollow tread.
Axle mass; axle dynamic behaviour; wheelset angle of attack; wheelset tracking position;Wheel back-to-back gauge; bearing acoustic condition; bearing defect classification (running surface/looseness)
Inter-axle misalignment; tracking error; rotation/warping, steering problem, lateral stability (hunting)
Mass; gross load; fore/aft balance; speed; AEI tag data
Length; mass; loading patterns; noisy tracking/dragging equipment; driving practices
Data fusion; composite alarms; predictive maintenance features; custom data outputs
CAPTION: Fig 1: This model shows the potential for damage arising from interaction of many different vehicle defects
CAPTION: Fig 2: Damage interaction. The development of a wheel defect recorded by a Teknis Wheel Condition Monitor (a) was also identified by the Vipac RailBAM system (b, c, d below)
CAPTION: LEFT: Fig 3: Damage propagation. Wheel defects on one axle were identified in September (blue), and by early January the wheels on the adjacent axle began to exhibit damage (red)
BELOW LEFT: Fig 4: Bogie geometry. A bogie which ran with a large tracking error and a small inter-axle misalignment (IAM) developed asymmetric wheel wear (w) and damaged flanges
CAPTION: Fig 5: A minor wheel defect detected in early May (a, red) developed into a major speed-dependent defect (b); looseness and fretting appeared in the bearing (c) and after five months the defective bogie caused a derailment
Supersite will advance wayside monitoring
The Supersite condition monitoring station has been developed by the Wayside Monitoring Alliance with a diverse range of sensors to identify defects on wagons as they pass at line speed. The Supersite demonstrates how withdrawing wagons for repair before serious damage occurs can offer financial savings, and the WMA proposes updating wagon interchange specifications to allow for improvements in measuring technology
Le suivi de l’état des wagons selon Supersite
Développé par la Wayside Monitoring Alliance, le poste de suivi d’état Supersite se compose d’une série diversifiée de détecteurs afin d’identifier les défauts des wagons alors qu’ils roulent à pleine vitesse. Le Supersite a démontré comment le retrait des wagons pour réparation, avant qu’interviennent des dommages plus importants, peut offrir des économies financières, et WMA propose la mise à jour des spécifications de l’interopérabilité des wagons afin de permettre des améliorations dans la technique de mesure
Supersite: Fortschritte bei der Wagen-Überwachung
Die von der Wayside Monitoring Alliance entwickelte Supersite-Betriebszustands-Überwachungsstation ist einer Anzahl Sensoren bestückt, welche Wagen-Defekte bei der Durchfahrt erkennen. Die Supersite-Station hat gezeigt, dass eine Ausserbetriebsetzung von Wagen zur Reparatur bevor schwere Schäden entstehen finanzielle Einsparungen bietet, und WMA empfiehlt die Spezifikationen zum Wagenaustausch zu aktualisieren, um die Fortschritte in der Messtechnik ausnutzen zu k