Application of portable Ultrasonic Phased Array Instrument for Rail Welds Ultrasonic Inspection Lao Jinjie a, Lu Chao b

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1 Advanced Materials Research Online: ISSN: , Vol. 717, pp doi: / Trans Tech Publications, Switzerland Application of portable Ultrasonic Phased Array Instrument for Rail Welds Ultrasonic Inspection Lao Jinjie a, Lu Chao b Key Lab. of Nondestructive Testing, Ministry of Education, Nanchang Hangkong University, Nanchang , China a laojinjie@163.com, b luchaoniat@163.com Keywords: Ultrasonic phased array; rail; aluminum-themic welding; ultrasonic testing Abstract: In order to promote the phased array technology for the application of weld inspection, the advantage of phased array technology was introduced and the application of rails welding inspection with phased array technology was also introduced. Through detecting nature and machining flaws of aluminum-themic welding of rails, contrast to results of conventional ultrasound test, validate the effectiveness of ultrasonic phased array method, concluding characteristics of ultrasonic phased array method for the aluminum-themic welding of rails. From the result of application, the efficiency of weld inspection could be greatly improved and the inspection cost could be greatly reduced by phased array technology. Introduction With the rapid development of Continuous Welded Rail (CWR), aluminum-themic welding as a seamless line of rail joint welding, by the advantages of its simple equipment, high joint stability, short operating time, and small space welding, aluminum-themic welding has been widely used on the railway in China. The principle of aluminum-themic welding is push high temperature molten steel into a special mold, after cooling and solidification, two joints will be welded together[1]. The inspection work for detect aluminum-themic welding is considered to ensure the safety of railway; detection methods are now commonly using the ultrasonic technology[2]. Basing on conventional ultrasound tests method to detect the aluminum-themic welding of rails, for different detecting regions, need to use different K property of probes, also, it is hard to detect the flaws of light spot and gray spot for the reason of signal reflecting, so utilizing focus and deflect of ultrasonic phased array to overcome conventional ultrasound tests method inadequacy. Through detecting nature and machining flaws of aluminum-themic welding of rails, contrast to results of conventional ultrasound tests, validate the effectiveness of ultrasonic phased array method, concluding characteristics of ultrasonic phased array method for the aluminum-themic welding of rails. Ultrasonic phased array inspection technology principle and equipment Phased array ultrasonic technology as an effective visual ultrasonic testing, the main feature is the computer-controlled excitation and receiving of individual elements in a multiple element probe. A phased array consists of multiple piezoelectric elements, and small wave fronts from those elements can be dynamically time-delayed and synchronized to steer and focus an ultrasonic beam [3]. It is possible that a properly designed phased array probe can perform several different inspections without changing hardware thereby reducing inspection time [4]. Two main characteristics of the phased array testing are flexible beam angle adjustment and dynamic focusing [5]. By the reasons of technology complexity and high input costs, domestic phased array ultrasonic transducers have been developed to serve in the area of medical diagnostics for many years [6-7], the B-type ultrasonic diagnostic apparatus has maturely applied by the dynamic focusing technology. The instrument Phasor XS and CTS-602 are all shown in figure 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,22:24:18)

2 Advanced Materials Research Vol Figure 1 Portable phased array ultrasonic flaw detector GE phasor XS and CTS-602 CTS-602 contains a pulse test and ultrasonic phased array detection modes, using the USB Interface can directly export the results to facilitate data storage. With 32 physical channels, supporting 16, 32, 64 or 128 probe array elements. Scanning modes include linear scan and sectorial scan, linear scanning beam adopts the same angle to scan electronically in one axis, sectorial scanning beam adopts the angle in a range to scan electronically. transmitted pulse width can be adjusted also. Detection experiments of ultrasonic phased array for aluminum-themic welding Instrument debugging and sensitivity adjustment: During phased array sectorial scanning, using 16 elements linear array probe as shown in figure 2(a).The distance between two crystals is 0.5mm, probe frequency is 4.0MHz, 36 wedge angle, adjusting sectorial scan angle from 30 to 70. During phased array linear scanning, using 64 elements linear array probe as shown in figure 2(b).The distance between two crystals is 1mm, probe frequency is 5.0MHz. (a) 16 crystals array S-probe (b) 64 crystals array L-probe Figure 2 Phased array probe There is no uniform ultrasonic phased array inspection standard to be reference now. Refer to ultrasonic testing of rail weld described in TB, using a special rail test block GHT-5 to certain sensitivity. Different regions of GHT-5 as shown in Figure3, the linear scan sensitivity determined by region-a, the sectorial scan sensitivity of rail head and rail web determined by region-b, the sectorial scan sensitivity of rail base determined by region-c. (a) region-a of GHT-5 block (b) region-b of GHT-5 block

3 386 Key Engineering Materials and Computer Science II (c) region-c of GHT-5 block Figure3 Different regions of GHT-5 block Detection experiment of Test specimen: In this study, aluminum-themic welding of sample1 containing machined defects; aluminum-themic welding of sample2 containing unknown nature defects. Sample1 designed by the Public Works Jiujiang section of Nanchang Railway Bureau, aluminum-themic welding of sample1 and defects location / size as shown in Figure4. Rail head and rail base hole 4mm diameter, rail waist cross-hole 5mm diameter. Where "A" means that the distance between the defect to the left side. Aluminum-themic welding of sample2 as shown in Figure5. Figure 4 Sample1 and defects location / size Figure 5 Sample2 Ultrasonic phased array test results and discussion of the machined defects in sample1: During the sectorial scanning, put the 16 crystals array S-probe on the rail tread to test the flaws of the rail head and the rail web, put the 64 crystals array L-probe on the rail base top slant surface to test the flaws of the rail base. The phased array sectorial scan result of sample1 as shown in Figure 6.

4 Advanced Materials Research Vol (a) No.1 flaw (b) No.2 flaw (c) No.3 flaw (d) No.4 flaw Figure 6 Result of phased array sectorial scan sample1 During the linear scanning, put the 64 crystals array L-probe on the rail tread to test the flaws in rail head and rail web, because of the size of the probe, phased array linear scanning for rail base has not been carried out. The phased array linear scan result of sample 1 as shown in Figure 6. The results show that artificial defects in a given location can find obvious defect image and verify the feasibility of phased array inspection experimental of aluminum-themic welding. In figure 6, the imaging of No.2 flaw in rail web clearly without interference noise. During testing the flaws in rail head and rail base, the imaging of No.1, No.3 and No.4 flaws are not satisfactory, need to use the formula to distinguish between real defect and reinforcement reflection. In figure 7, since the existence of beginning of the probe wave and blind area, the imaging of No.1 flaw in rail head has low signal to noise ratio. The imaging of No.2 flaw in rail web is also clear without interference noise. (a) No.1 flaw (b) No.2 flaw Figure 7 Result of phased array linear scan sample1 Ultrasonic phased array test results and discussion of the unknown nature defects in sample2:using the above method of ultrasonic phased array inspects the defects which are unknown nature defects in sample 2. The phased array sectorial scan result of sample 2 as shown in Figure 8. No defect has been found by ultrasonic phased array linear scanning.

5 388 Key Engineering Materials and Computer Science II (a) No.1 flaw (b) No.2 flaw Figure 8 Result of phased array sectorial scan sample2 Ultrasonic phased array testing for aluminum-themic welding of rails can detect conventional methods cannot cover area. Flexible to control the beam scan angle through phased array sectorial scanning. No.1 flaw exists in rail head, No.2 flaw exists in rail base. Note the defect location and equivalent size, the data comparison between conventional ultrasonic pulse test and phased array sectorical scan as shown in Table 1. Table 1 The defect location and equivalent size comparison between conventional ultrasonic pulse test and phased array sectorial scan Scanning mode Flaw Number Depth (mm) Distance from the weld center (mm) Equivalent size (db) phased array sectorial scan conventional ultrasonic pulse test No φ3-27 No φ3-6 No φ3-25 No φ3-4.5 From the data in table 1, verify the feasibility of phased array inspection experimental of aluminum-themic welding further. Comparing with conventional ultrasonic pulse test, phased array scan not only can detect the size and location of defects, but also effectively shorten the detection time, well overcome the difficulties of detect slowly and easily missed detection in conventional ultrasonic pulse testing. Conclusion From the above experimental results and analysis can be drawn: (1)By comparing groups of experiments, verify the feasibility of phased array inspection experimental of aluminum-themic welding. (2)Since the interference of weld reinforcement, phased array imaging of rail web is better than rail head and rail base. (3) Comparing to conventional ultrasonic pulse testing, phased array inspection for aluminum-themic welding has the characteristics of high detection speed, high efficiency, probe energy sufficient, excellent performance of repeated and good effect of imaging, etc. Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant No , )

6 Advanced Materials Research Vol Reference [1] FAN You-gang. Analysis on the Welded Head Failures of Rails Thermit Welding and the Control Measures[J]. SCI-TECH INFORMATION DEVELOPMENT & ECONOMY, 2007, 17(26): 260~262. [2]XIE Min, FENG Jian, LEI Dai-Ming. Study and prevention of defects in rail thermit welds [J]. Journal of Southwest University for Nationalities (Natrual Science Edition), 2006,32(2):339~341. [3] R/D Tech guideline., Introduction to Phased Array Ultrasonic Technology Applications, R/D Tech inc., Quebec, Canada, [4] Paul A Meyer, J W Anderson. Ultrasonic Testing Using Phased Arrays [In]. Proceedings of 15th World Conference on NDT [CD].Room, Italy: [5]LI Yan. New Technology of Ultrasonic Phased Arrays for steel welding [J]. NONDESTRUCTIVE INSPECTION, 2002, 3:1~5. [6]R.Huang, L.W.Schmerr Jr., and A.Sedov. A NEW MULTI-GAUSSIAN BEAM MODEL FOR PHASED ARRAY TRANSDUCERS. Review of Quantitative Nondestructive Evaluation, 2007, V ~758. [7]XU Xi-gang, SHI Ke-ren, CHEN Yi-fang, etc. DEVELOPMENT OF ULTRASONIC PHASED ARRAY NONDESTRUCTIVE TESTING SYSTEM [J]. NDT, 2004, 26(3):116~119.

7 Key Engineering Materials and Computer Science II / Application of Portable Ultrasonic Phased Array Instrument for Rail Welds Ultrasonic Inspection /