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The present invention relates to a method for monitoring and managing defects in the rails and switches of a metro-railway line.
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The defects may be native or fatigue-induced.
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The rails of metro-railway lines, due to the repeated passage of railway vehicles, are subjected to fatigue cycles caused by bending and shear stresses.
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It is known that fatigue cycles, if of sufficient magnitude, cause existing cracks in the material subjected to fatigue to propagate, while at the same time triggering the formation of new cracks starting from small material imperfections, surface indentations, corrosion phenomena, geometric irregularities in welded joints, or failure of mechanical joints.
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If sufficiently extended, the cracks significantly reduce the strength of the material, leading, in certain cases and under specific conditions, to fracture.
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Fracture usually occurs at moments of maximum stress, which in the case of metro-railway lines corresponds to the passage of a train.
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The fracture of a rail under a passing train may have various consequences, ranging from a simple jolt of the subsequent wheels to derailment with the potential for a serious railway accident. For this reason, metro-railway line operators typically try to limit rail fractures as much as possible by periodically or occasionally inspecting the entire length of a track or sampling the least resistant points, such as welds.
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The issue of rail fractures is particularly critical on metro lines, since they are subjected to far more frequent fatigue cycles than mainline railways, with train passage frequencies that may reach one train every 90 seconds.
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For this reason, despite sporadic inspections, as shown by studies and surveys carried out among operators of major metro systems worldwide, a metro network may experience several dozen rail fractures per year if an appropriate defect monitoring and management method is not properly implemented.
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There is therefore a need for a method that allows metro and railway rails to be monitored methodically and systematically, and for all technical information derived from inspections to be managed in an optimized manner so as to generate coherent maintenance actions with the aim of drastically reducing the annual number of fractures.
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The technical task addressed by the present invention is therefore to devise a method capable of eliminating the technical drawbacks complained in the known art.
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Within this technical task, an object of the invention is to provide a method that minimizes the annual number of rail fractures.
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The technical task, as well as these and other objects, are achieved, according to the present invention, by implementing a method for monitoring and managing defects in the rails and switches of a metro-railway line according to claim 1.
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Other features of the present invention are further defined in the subsequent claims. Additional characteristics and advantages of the invention will become more apparent from the description of a preferred but not exclusive embodiment of the method according to the invention, provided by way of example and not limitation in the accompanying drawings, in which: Figure 1 shows the location and extent of a defect detected by the first sensor system, with a B-SCAN representation showing rail length on the x-axis and rail height on the y-axis; Figure 2 shows the location and extent of five defects on five different rails detected by the second sensor system, using the same reference axes as Figure 1, where the first defect is a transverse crack in the head at an aluminothermic weld, the second defect is a transverse crack in the head at a flash-butt weld, the third defect is a horizontal crack in a flash-butt weld, the fourth defect consists of anomalous holes in a glued insulated joint, and the fifth defect is a transverse crack in full rail, of external origin;
Figure 3 shows a table forming part of the database.
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With reference to the figures mentioned, a method is shown for monitoring and managing defects in the rails and switches of a metro-railway line.
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The defect monitoring and management method 1 provides for an initial new scan of at least a section of the metro-railway line carried out by a first ultrasonic sensor system.
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The initial new scan takes place following the first installation of the section of the metro-railway line, after a repair of the line section, and at scheduled periodic intervals.
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The first ultrasonic sensor system is located on board a motorized rolling vehicle in continuous movement along the section of the metro-railway line.
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This motorized rolling vehicle is capable of travelling along the entire metro-railway line, which may be a metro line, and during the journey it detects the presence of any defects in the two rails 2 forming the track along which it moves.
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In particular, the motorized rolling vehicle is a diagnostic machine, for example the US1-10 inspection trolley by Speno International, equipped with an ultrasonic inspection carriage featuring two sliding sliders, each comprising 8 ultrasonic probes, and provided with a SOCO-8P-UT ultrasonic signal acquisition unit by Socomate International S.A. for detecting defects through ultrasonic non-destructive testing.
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Each slider containing the 8 ultrasonic probes is designed to slide along one of the two rails on which the motorized rolling vehicle travels, remaining coupled for the purpose of transmitting ultrasonic impulses by means of a thin film of water.
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The eight ultrasonic probes are designed to inspect every internal point of the rail, and are therefore positioned at different points on the surface or have different orientations.
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The orientation of the probes may correspond to the typical angles of ultrasonic probes: flat probes at 0°, 35°, 55°, and 70°.
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The method then provides for the creation of a database containing all detections of potential defects 1, including at least the indication of the positions and dimensions of the potential defect signals 1 detected by the first sensor system.
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The position and size of the defects 1 detected by the first sensor system are therefore entered into the first database.
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Detection of defects 1 may also be performed through visual observation by technicians or operating personnel, or as a result of a specific report.
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In other words, if a technician working on the metro-railway line, or a train driver operating on the line, notices any imperfection in the tracks, they report it, and the imperfection is entered into the database in the same manner as the potential defect indications detected by the first sensor system mounted on the self-propelled rail vehicle.
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The method then provides for an initial validation of the new potential defect indications by overlapping and comparing them with those already entered in the database during previous periodic scans, which constitute the historical record of known indications associated with the monitored metro-railway line.
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Indeed, the database is configured to perform simultaneous analysis of all available information acquired during periodic scans of the metro-railway line, regardless of whether each individual defect indication was detected during the latest scan or during previous scans, or whether the indication resulted from visual observation by personnel or from a specific report.
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The database is also configured to keep maintenance management of all known defects 1 on the metro-railway line under control, even if the first ultrasonic sensor system on board the motorized rolling vehicle is unable, during a scan of the metro-railway line, to maintain proper coupling with the rails under inspection and therefore cannot reliably detect all defects actually present in the scanned rails.
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The method then provides for a second new scan of all locations of the indicated potential defects 1 stored in the database, both new and from previous scans, using a second portable ultrasonic sensor system for the final confirmation of defects, the separation of false indications or false positives, and the assignment of a class and precise dimensions to the confirmed defects 1. The second new scan is carried out within a predetermined time after the detection of the defects 1.
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The second new scan is performed by a certified operator in accordance with the applicable international technical standards for Non-Destructive Testing, who then goes directly onto the tracks of the metro-railway line to manually inspect, using the second portable ultrasonic sensor system, the potential defect indications 1 previously detected by the first sensor system or simply reported by passenger train drivers or technical maintenance personnel working on the track. The certified operator applies certified inspection procedures, using different types of ultrasonic probes appropriately in order to identify, classify, and size each individual defect. This operation is carried out because the second sensor system, operated directly by a certified human operator, is far more precise and reliable than the first sensor system, which is automatically moved by the motorized rolling vehicle progressing at a preset speed along the track, thus having very limited dwell time over the defects to be detected.
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Scanning with the first sensor system therefore serves as an initial screening for identifying potential defect indications that must then be confirmed, classified, and sized using the second sensor system.
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The second sensor system is thus used according to the criteria defined by a specific inspection procedure to confirm whether the potential defect indications are actual integrity defects in the rails 1 or false indications, and to determine the size of the defects 1, their orientation, their classification, and their location not only along the metro-railway line but also within the cross-section of the rail 2 or switch.
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The longitudinal location along the metro-railway line had already been determined during the initial new scan; therefore, this step merely confirms the actual position of the defect, understood as the distance from a known point on the metro-railway line, for example, a station, a switch, or a weld.
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Localization within the cross section is instead required, since, for an equal defect size, a defect 1 is more or less critical depending on whether it is located in the rail head, in the web, or in the rail foot.
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Cross-sectional location must necessarily be performed using the second sensor system because it requires multiple passes of the ultrasonic probes over the area of interest and real-time interpretation of the acquired results, an approach incompatible with the first automatic sensor system on board the motorized rolling vehicle, which progresses continuously along the metro-railway line.
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The certified operator then assigns each defect 1 a class depending on its size and cross-sectional position.
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Classification is therefore carried out by the certified operator, distinguishing the detected defects 1 by size and/or orientation and/or cross-sectional location within the rail 2 or switch. The classification of the detected defects 1 is performed by assigning each detected defect 1 an alphanumeric severity code corresponding to a scale of increasing defect severity.
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The method also provides for the coding of a segment of the metro-railway line that contains the classified defect 1.
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This coding serves to enable easier future identification of the position of defect 1. The unique numerical code of each individual defect consists of four digits, a hyphen, and two digits: the first digit identifies the sequential number of the scan campaign performed in the current year; the next three digits identify the sequential number of the defect detected during the ongoing scan campaign; the two digits after the hyphen indicate the current year.
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Each detected and confirmed defect 1 is classified by assigning, in the database, an identification code corresponding to the defect type, according to the rules of the defect inspection procedure for rails adopted by the operator managing the metro-railway network. Each detected and confirmed defect 1 is also assigned a code identifying the severity of the defect, expressing the intervention priority: the alphanumeric code typically used is a number between zero (less severe) and four (most severe).
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Each detected and confirmed defect 1 is therefore also associated in the database with a specific dedicated intervention.
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The dedicated intervention for defects 1 classified with the lowest severity code consists of scheduled periodic inspection through an additional second new scan. Defects classified as zero are therefore re-inspected with a second new scan every four months. The dedicated intervention for defects 1 classified with a severity code higher than the lowest provides for resolution through a specific maintenance action within a predetermined time limit. The predetermined time limit for managing defect 1 becomes longer in inverse proportion to the severity of defect 1.
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In particular, the predetermined management time for defect 1 is:
- 60 days for class 1 defects;
- 30 days for class 2 defects;
- 10 days for class 3 defects, with the possibility of totally or partially restricting train circulation along the affected section of the metro-railway line, or reducing train transit speed along that section;
- 0 days for class 4 defects, which therefore require immediate management, resulting in the immediate suspension of train traffic along the affected section of the metro-railway line until the defect 1 has been resolved.
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As shown in Figure 3, a class 2 defect such as the one in the first row of the table is less severe than the class 4 defect shown in the third row; therefore, it has a much longer management timeframe, as indicated in the last column under "scans with second sensor system."
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The defect in the second row of the table, class 0, does not require a dedicated intervention, because class 0 defects only require another inspection every four months; consequently, the last columns of the table are left blank.
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A dedicated intervention is therefore carried out for each classified defect 1.
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The dedicated intervention may be temporary or permanent, and if temporary, it must be followed by a permanent intervention within a deadline established by the temporary intervention, in accordance with the prescribed defect control and management procedure.
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The temporary intervention may be carried out if defect 1 is of class from one to four, and includes a phase of securing the rail affected by defect 1 through the installation of a mechanical joint consisting of tightened clamp plates, an operation referred to as "fish-plating" of the defect. This fish-plating may be performed using bolted clamp plates, requiring the drilling of 4 holes in the rail web, if the defect is class one to four, or by using clamps if the defect is class three or four: this choice depends on the type of defect present.
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If fish-plating is performed using bolted clamp plates, the subsequent permanent intervention must be carried out within:
- 90 days for class 1 or class 2 defects;
- 30 days for class 3 defects;
- 30 days for class 4 defects, with a simultaneous reduction in train speed along the affected section of the metro-railway line containing defect 1.
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If instead the fish-plating is performed using clamps, the subsequent permanent intervention must be carried out within:
- 15 days for class 3 defects 1;
- 15 days for class 4 defects 1, with a simultaneous reduction in train speed along the affected section
of the metro-railway line containing defect 1.
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The permanent dedicated intervention consists of a new scan using the second sensor system, or repair by applying material via electrode welding in the defected area followed by grinding, or the replacement of an entire rail bar up to 200 metres long, made up of several standard 18-metre rail bars welded together, or the replacement of a simple rail section with a minimum length of 6 metres, to replace the rail segment containing the classified defect 1.
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Replacing an entire rail bar of up to 200 metres, preferably performed when the rail containing defect 1 shows high wear levels, albeit within acceptable limits, also allows for renewal of the metro-railway line tracks.
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Finally, a result is associated in the database for each dedicated intervention, to keep track of the actions performed on the metro-railway line.
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Modifications and variations, beyond those already mentioned, are naturally possible.
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It has been observed in practice that the method according to the invention is particularly advantageous because it allows the entire metro or railway line to be kept under control. In this way, it becomes possible to identify with great precision the position of existing defects as well as their hazard to the structural integrity of the rail, enabling continuous monitoring of the condition of the metro-railway line.
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The benefit of the method derives from the simultaneous analysis of all available information acquired during periodic scans of the metro-railway network, regardless of whether each individual defect indication was detected during the latest scan or earlier scans, or whether the indication arose from visual inspections performed by maintenance personnel on the line or from simple reports by passenger train drivers.
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This method therefore overcomes the intrinsic limitations of defect scanning performed with a self-propelled rail vehicle equipped with a first ultrasonic sensor system, since during a scan, carried out with the self-propelled vehicle in motion along the track under examination, it cannot be guaranteed that the said first ultrasonic sensor system is always correctly coupled with the rails and can reliably detect all defects that are actually present in the scanned rails.
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It is therefore possible to replace damaged rails or rails containing cracks before they reach the point of fracture, thus preventing them from breaking during the passage of a train. Thanks to the method described, the number of annual rail fractures on a metro network can be reduced from several dozen to three or even fewer.
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The method for monitoring and managing defects in the rails and switches of a metro-railway line, as conceived, is susceptible to numerous modifications and variations, all of which fall within the scope of the inventive concept; moreover, all details may be replaced with technically equivalent elements.
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In practice, the materials used, as well as the dimensions, and especially the ultrasonic sensor technology employed, may be of any type depending on requirements and the state of the art.