11th European Conference on Non-Destructive Testing (ECNDT 2014), October 6-10, 2014, Prague, Czech Republic Evolution of ultrasonic inspection techniques on railway axles More Info at Open Access Database www.ndt.net/?id=16661 Cristina GILARDONI and Collaborators 1 1 Gilardoni S.p.A., Mandello del Lario (LC), Italy; cgil@gilardoni.it Abstract Considering solid and hollow railway axles, reliable non-destructive inspection techniques and procedures are required in order to guarantee the structural integrity during service. Axles are periodically inspected by the ultrasonic method (UT) during maintenance interruptions in first level workshops without need to be disassembled, while the magnetic particles test is carried out in second level workshops after wheelset disassembly. UT inspections of solid axles can be performed by a rotating probe applied to the ends of solid axles, whilst hollow axles can be tested with boreprobes roto-traslating along the longitudinal bore. In terms of inspection reliability, great developments have been introduced over the last years, especially focusing the aim to improve the capability of instruments to prevent human errors (a very sensible topic always present in EU technical discussions) thanks to automatic instrumentations and guided procedures. From this point of view, the present paper aims to present and discuss such developments, considering the evolution of the rotating probe and boreprobe inspection instrumentations: starting from their origin in the analogic era through the introduction of digital applications, the experimental and numerical characterization of their capabilities and performance, the present status and, finally, near future developments and improvements. Keywords: Railway axles, rotating probe, boreprobe, ultrasonic inspection, inspection reliability 1. Introduction The aim of this paper is to briefly describe Gilardoni's recently developed solutions for the railway field. Four products will be presented: the RDG 3000F PA and the automatic rotating probe, dedicated to solid axles inspection during maintenance, the automatic system for hollow axles inspection (BAT) and the RDG 4000 TR for railway wheels residual stress measurement. 2. RDG 3000F PA, the new frontier of solid axles inspection According to its great knowledge in ultrasonic inspections, Gilardoni S.p.A. has recently developed a new traditional single channel ultrasonic equipment with an integrated Phased Array module 16:64, mostly dedicated to the inspection of solid axles (Fig. 1). The dimensions of RDG3000F PA are 351x239x134 mm and the weight is approximately 4.7 kg. The equipment has a touch-screen anti-glare display, TFT type, with a diagonal of 10.4 and a resolution of 1024x768 pixels at 60Hz. The maximum brightness is 400cd/mq with a contrast of 1200:1. The UT main characteristics are: - Range of PRF: 50 5000 Hz - Transmitter voltage up to 400 V, adjustable bipolar square wave plus burst function - Four linear gates - Maximum amplification: 110dB. Variation steps: ±0,1 db, ±0,5 db, ±1 db, ±2 db, ±6 db, ±12 db - Tuned filters, wide - Pulse/Echo and Dual - DAC and TGC curves, built with 10 or more points set by users - AWS, DGS, CSC, Trigonometric, Echo-Echo functions - Range of ultrasonic velocity: 1500 10000 m/s - Sampling frequency: 100 MHz at 12 bit - Ethernet connection
- USB ports to connect the equipment to PC, mouse, external keyboard, and external memory. The Phased Array module characteristics are: - 16:64 configuration - Encoded/Temporal recording - Transmitter: o Bipolar square wave with maximum voltage 200 Vpp o Maximum PRF: 5 khz o Pulse width: 20 500 ns - Receiver: o Maximum amplification: 80 db. Variation step: ±0,1 db o Bandwidth (at -3 db): 0.5 15 MHz o Digital filters, wide - Time resolution: 2.5 ns - 256 focal laws active at the same configuration - Four linear digital gates - DAC and TGC curves. The equipment is IP 54 certified and powered by two batteries. Battery life is about 8 hours with medium brightness of the display, PRF adjusted at 500 Hz and using a single channel or Phased Array module. Recharging time is about 3 hours. 2.1 What s new and why different? Figure 1. RDG 3000F PA and rotating probe for railway inspection More than a portable flaw detector, the RDG 3000F PA can be considered a semi-automatic system for UT inspections. The SW has been developed to allow the inspector (administrator) to create customized control procedures (Fig. 2). The main goal is the reduction of human errors that can occur during the setup of the instrument. Different users and different access levels (administrator, level 1, level 2) can be created to avoid files corruption or configuration mistakes. At every single start up, user name and password are requested. Another main feature of the RDG 3000F PA is the recording capability, fully optimized for railway inspections. A-Scan and B-Scan presentations are constantly disposable on the screen during the exam. A smart connection between the flaw detector and the rotating probe increases the reliability of the inspection: probes holder configuration, active transducer and inspection speed are constantly monitored.
The rotating probe can be programmed by mean of the RDG 3000F PA. The inspection is allowed only in case of complete matching between the parameters included in the technical instruction and the configuration of the rotating probe. 2.2 Keyword: complete data recording Figure 2. Wizard for control procedures creation The RDG 3000F PA can be used in three different modalities, briefly described in the following. - Manual inspection: independently from the selected authentication level, this inspection modality allows the operator to use the equipment as a traditional UT equipment. - Manual inspection using technical instruction: it is possible to carry out inspections with one or more transducers previously organized in a configuration archive. For each transducer it is possible to set gates, sensitivity, inspection curves, etc. After choosing the technical instruction relative to the exam to be performed, the equipment provides a wizard tool to calibrate each probe. Only when the calibration has been carried out the inspection is allowed. During an exam, the system automatically recalls (one by one and in a predetermined order) the settings files. The user interface is smartly organized to allow easily recognition of ultrasonic indications by means of a temporal B-Scan and real time A-Scan. Results are stored in a.zip file which contains the B-Scan image, the identification file and, if necessary, the selected A-Scans. - Inspection with rotating probe using technical instruction. The control is carried out by a series of single crystal transducers (operating with longitudinal waves and different frequencies and refraction angles) installed on a state-of-the-art probes holder. After having chosen the technical instruction relative to the exam to be performed, the equipment provides a wizard to calibrate each probe. Only when the calibration has been carried out the inspection is allowed. The system acquires one A-Scan every 0.5 of rotation of the rotating probe; the probe rotates for 360, so 720 A-Scans are acquired (Fig, 3). During the test, the flaw detector checks continuously the rotational
speed. If the speed is greater than the maximum allowed, the system automatically aborts the inspection. At the end of acquisition, the last A-Scan is visualized on the monitor together with the B-Scan of the entire exam. The same procedure is performed for all transducers. All the results can be saved on the equipment. Results are stored in a.zip file which contains the B-Scan image, the identification file and all the acquired A-Scans. Figure 3. Exam execution (left) and results review (right) 3. Gilardoni s 3 rd generation automatic system for hollow axles inspection 3.1 Hardware innovations After more than 20 years of continuous developments, Gilardoni has reached its third generation of systems for high speed trains hollow axles inspection (BAT) (Fig. 4). Figure 4. The 3 rd generation BAT Compared to the previous BAT units, the new one is smaller, allows single-side inspection and quick replacement of probes-holder. The BAT unit has been designed to be easily transportable thanks to its compact dimensions: 2030 mm long, 1125 mm deep and 1285 mm
high. Total weight is about 850 kg. A self-propelled system allows the unit to move on plane surfaces and to climb over a slope up to 15%. A powerful brand new UT electronics increases the device performances: higher signal-tonoise ratio, PRF and voltage values can now be reached. Exams can be carried out through up to ten transducers (for bore diameters greater than 60 mm), up to six angled beam transducers with ultrasonic beams oriented in the axial directions of the axle (forward and backward), two secant beam probes (clockwise and anticlockwise) and one (or two) optional straight beam transducers for peripheral volumetric flaws. Transducers are hosted in a state-of-the-art probes-holder, which is able to rotate at a controlled peripheral speed (Fig. 5). Figure 5. 65 mm (upper) and 30 mm (lower) probes holders In the front part of the machine is placed the mechanics for the lifting and positioning of the control unit, which enables the probes-holder to be inserted into the axle. Coupling is ensured by an oil delivery system regulated by pressure-meter and flow-meter. A posh cabinet contains multi-channel ultrasonic electronics, industrial personal computer, motors drivers, contactors, UPS device and hydraulic circuit. A new software is able to manage operating processes, to set up inspective sequences, to record, store and recall data and A-Scans, to manage sensor systems and alarms; two 17 touch screen displays clearly visualize all the events and make the machine comfortable to use. The first one is fully dedicated to system managing software (Fig. 6); the second is dedicated to the UT software. Figure 6. Auto learning program for definition of the inspection procedure
Inspection time can be significantly decreased compared to the second generation BAT unit. It can be estimated in 10 / 12 minutes for the whole axle but it depends, of course, by the shape and the length of the axle itself. The inspection range of the bore diameter is now extended between 30 to 90 mm with the same arm, but different probes holder. The inspection is performed from one side only and can cover all the length of the axle. A new concept system allows the probes-holder to move inside the axle, ensuring an axial inspection up to 2400 mm. The inspection sequence foresees a continuous rotation of the probes-holder, followed by an axial step of predefined value, which can be set in the auto-learning program. In the auto-learning program is now possible to setup one transducer at a time and a special software merges the results in a unique program file. The parameters that can be adjusted for every step are gain, gates position and gate lengths. 3.2 Fully exhaustive presentation of exam results The new software has been developed to ensure a complete post processing analysis. All the instruments for an accurate evaluation of indications are provided; in addition to the classical tabular representation of flaws (flaws list) (Fig. 7), the software make disposable C-Scan, B- Scan, A-Scan and 3D representation for each transducer. Different colours for different probes are used to help the operator in the analysis process. Figure 7. Report window and flaw list Smart cursors and adjustable zoom allow easy selection and interpretation of flaws (Fig. 8). The 3D visualization is a super powerful instrument to help to predict the evolution of flaws.
Figure 8. B-Scan and related A-Scan 4. New technologies and latest developments 4.1 RDG4000 TR RDG4000 TR represents Gilardoni s solution to measure residual stresses in railway wheels by means of the technique of acoustic birefringence. This measure shows how the transmission velocity of ultrasonic waves is subject to the different stress status of tested wheels sections. The device refers to EMAT transducers, whose advantage consists in the capability to transmit ultrasonic waves without coupling. The EMAT probe is composed by two equal coils, orthogonally disposed, to produce transversal waves with linear polarization in two different planes (parallel and perpendicular to the rolling plane of wheel). The acoustic birefringence is measured by means of correlations in time of flight related to each first back wall echo. Fibrous texture is also taken into account. For each point, it is measured the average of circumferential stress below the rim of the wheel. The EMAT probe can be displaced along the radial direction by a mechanical probe holder, which can be easily placed and locked on the wheel by two magnets; scanning allows collecting data from different points located along the radial direction (Fig. 9). The residual stress is measured according to the velocity variation (if any) of the shear waves in two different reference planes. If the velocity variation is negligible, the residual stress is approximately insignificant. If the velocity variation is not negligible, it means that there is a stress condition and it could be measured by means the acoustoelastic coefficient. All the measures and graphs collected during an inspection can be stored in a.zip file and easily exported (and stored) in an external PC.
4.2 Automatic rotating probe Figure 9. Main screen of RDG 4000TR The new automatic rotating probe developed by Gilardoni S.p.A. (Figs. 10 and 11) is a further innovation of the traditional rotating probe previously described. It represents the state-of-theart of solid axle s inspection systems. If connected to a RDG 3000F PA, further possible human errors can be avoided. Thanks to newly designed transducers, coupling is constantly ensured during the automatic rotation. Like the traditional rotating probe, also this new mechanics is equipped by electronics that can be programmed according to installed transducers. Other main hardware characteristics are: - Minimum axle journal 128 mm - Operating diameter of transducers 95 mm - Length 500 mm, weight 7.5 kg - Fixing by means of Neodymium magnets - Automatic rotation guaranteed by brushless motor with internal actuator. The rotational speed can be adjusted (two different values, normal and fast) - 20 hours of continuative inspection guaranteed thanks to powerful batteries on board - Automatic/manual rotation thanks to a mechanical clutch - Up to five transducers can be installed - Bidirectional high-resolution encoder - IrDA remote control 5. Conclusions Thanks to these products, Gilardoni S.p.A. confirms its primary role in the development of NDT solutions, especially concerning the railway field. The tight cooperation with its technical partners like LucchiniRS and Politecnico di Milano and its main customers like, Trenitalia, Trenord, Alstom, CNR-CRC, CSR-SIFANG, CAF and Valdunes has given (and will give) useful and conspicuous results.
Figure 10. Automatic rotating probe - table Acknowledgements Figure 11. Automatic rotating probe connected to a freight axle The authors would like to thank Mr. S. Cantini (LucchiniRS), Prof. S. Beretta (Politecnico di Milano) and Dr. M. Carboni (Politecnico di Milano) for the useful technical and scientific help.