Nội dung

N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 Available online at ScienceDirect Nuclear Engineering and Technology journal homepage: www.elsevier.com/locate/net Original Article Thin-Plate-Type Embedded Ultrasonic Transducer Based on Magnetostriction for the Thickness Monitoring of the Secondary Piping System of a Nuclear Power Plant Taehoon Heo a,b and Seung Hyun Cho a,b,* a Center for Safety Measurement, Korea Research Institute of Standards and Science, Daejeon, 34113, Republic of Korea b Department of Science of Measurement, Korea University of Science and Technology, Daejeon, 34113, Republic of Korea article info abstract Article history: Pipe wall thinning in the secondary piping system of a nuclear power plant is currently a Received 12 April 2016 major problem that typically affects the safety and reliability of the nuclear power plant Received in revised form directly. Regular in-service inspections are carried out to manage the piping system only 16 May 2016 during the overhaul. Online thickness monitoring is necessary to avoid abrupt breakage Accepted 18 May 2016 due to wall thinning. To this end, a transducer that can withstand a high-temperature Available online 16 June 2016 environment and should be installed under the insulation layer. We propose a thin plate type of embedded ultrasonic transducer based on magnetostriction. The transducer was Keywords: designed and fabricated to measure the thickness of a pipe under a high-temperature High Temperature Magnetostrictive Transducer Nuclear Power Plant Secondary Piping System Shear Horizontal Wave Wall Thinning condition. A number of experimental results confirmed the validity of the present 1. transducer. Copyright © 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ Introduction Wall thinning of a secondary piping system is a critical issue related to the safety of nuclear power plants (NPPs). This condition can even lead to fatalities when, for instance, the main feed-water pump has an elbow rupture, as occurred in the Surry Unit 2 in the USA or when the condensate system has a straight pipe rupture, such as in Mihama Unit 3 in Japan [1]. licenses/by-nc-nd/4.0/). Accordingly, a secondary pipe with a thin wall must be supervised under careful control. This is mainly managed with thickness measurements using ultrasonic waves. However, the secondary pipe has various thicknesses and shapes, and it is typically too long to be inspected. Furthermore, most of the pipe is covered with heat-insulating material that must be removed before ultrasonic testing can be performed. This makes inspections difficult to carry out during the operation of * Corresponding author. E-mail address: seungcho@kriss.re.kr (S.H. Cho). http://dx.doi.org/10.1016/j.net.2016.05.007 1738-5733/Copyright © 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 the NPP. Generally, during the overhaul of an NPP, ultrasonic nondestructive testing is conducted to measure the thickness of pipes. All NPPs have management plans specific to pipe wall thinning [2e4], and the target objects to be managed in the thousands or more. In-service inspection tasks should be done during the overhaul roughly every 18 months. Regular monitoring is necessary when the pipe becomes thinner than a certain standard. Thus, online thickness monitoring techniques are required to determine the progress of wall thinning. During the operation of the plant, the working temperature of the secondary piping system can reach as high as 300
C. Consequently, conventional ultrasonic transducers cannot be applied due to their low working temperature range. As a result, a new transducer capable of withstanding a hightemperature environment is necessary. In an effort to develop such a device, various studies of high-temperature transducers [5e7] and methods that use a waveguide to avoid direct contact with the heat-affected zone [8e14] have been proposed. Among them, Nisbet [8] reported a water or liquid waveguide for thickness measurements in the roles of both a couplant and a coolant. Cegla et al [9e11] reported a crack and wall thickness monitoring method that uses shear horizontal (SH) waves with dry-coupled waveguide transducers. Hernandez-Valle and Dixon [12,13] reported the design and testing of a high-temperature electromagnetic acoustic transducer with a pulsed electromagnet. Ashish et al [14] reported a rod-type magnetostrictive transducer (MsT) for in-situ inspections with a longitudinal wave. An insulation layer covers numerous pipes to protect them and to retain heat. In this situation, a transducer installable under the layer is necessary for structural health monitoring. Such a transducer must be very thin to be embedded between the surface of a pipe and its insulation layer. Waveguide transducers are not appropriate in such a case because of installation problems. In this study, we propose a thin-plate-type transducer that satisfies the requirement of install ability under the insulating layer in the secondary piping system of a NPP. The proposed transducer can be applied in a high-temperature condition, and it was fabricated based on magnetostriction fundamentals for a very thin shape. Magnetostriction refers to the coupling phenomenon between a magnetic field and mechanical deformation. Ultrasonic waves then can be generated and measured using this principle. This phenomenon occurs in a ferromagnetic material and its alloys. The magnetostriction disappears beyond the Curie temperature of the material [15]. Ironecobalt (FeCo) alloy, used in this work, can be sufficiently applied to a temperature of approximately 300
C, the maximum operating temperature of a secondary piping system, as its Curie temperature reaches nearly 940
C [16]. Generally, an MsT is composed of a magnetostrictive material, a coil, and a magnet. The coil and the magnet can be manufactured to endure a hightemperature condition. Very thin plate-type transducers can be fabricated because the FeCo alloy can be formed with a thickness of 0.15 mm in this work. The coil and the magnet can also have a thin form. Hence, each component of the transducer is designed to be thin to measure the pipe thickness. To design the transducer, an analysis model was initially established for an acoustic 1405 field analysis, after which the layout of the coil was devised. Finally, a prototype transducer was fabricated to a thickness of approximately 3 mm. Subsequently, several tests were conducted to verify the transducer, during which the hightemperature characteristics of the transducer were assessed. In the experiment, we observed the effect of the bias magnetic field of the transducer. Eventually, the fabricated prototype transducer was tested in a performance evaluation for hightemperature conditions and to determine the wall thickness. The transducer showed sufficient performance to detect them. In conclusion, for this study we developed a thin-platetype MsT that can be embedded between the surface of a pipe and its insulation layer. This permanently installable transducer will be a useful tool for monitoring the wall thicknesses of pipes in the high-temperature environments of secondary piping systems of NPPs. 2. Design and fabrication of the thin-platetype embedded MsT 2.1. Principle of the MsT An MsT can generate and detect ultrasonic waves based on the magnetostrictive effect [17]. The effect denotes a relationship between material deformation and magnetic field induction. Thus, an MsT is only applicable to a ferromagnetic material and its alloys. Typically, the MsT is comprised of magnetostrictive patches, actuating and sensing coils, and permanent magnets (or electromagnets). These components should be deployed to transduce specific ultrasonic waves. Fig. 1 depicts the patch-type MsT. It can easily transmit and receive SH waves in this arrangement [16]. It also operates via the magnetostriction of the ferromagnetic patch materials. An MsT uses actuating and sensing coils to create a dynamic magnetic field and permanent magnets to produce static magnetic field. The cross combination of these magnetic fields can be converted to the shear deformation of the patch. Hence, SH waves are propagated on the patch and the waves are conducted from the patch to direct-coupled materials. A patch-type MsT usually has higher sensitivity than a noncontact-type MsT, because a magnetostrictive patch is mechanically coupled to the structure and the material of the patch deforms better than a general ferromagnetic Fig. 1 e Schematic of the magnetostrictive transducer utilizing shear horizontal waves. 1406 N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 material. For this reason, a patch-type MsT can be used for all materials that ultrasonic waves can propagate because the patch transducer is directly coupled with a specimen. Thus, when the noncontact feature is absolutely necessary, a noncontact-type MsT should be selected. Otherwise, a patchtype MsT is favorable for higher sensitivity of the transducer. Fig. 2 shows transducer component arrangement for SH bulk wave transduction. The ferromagnetic patch and specimen are coupled and the intended wave on the patch transmits to the specimen. The wave drives into the specimen with specific directivity and power (i.e., the focusing location) depending upon the characteristics of the coil [18]. In addition, if we adjust the interval of the contiguous coils or send the electric signal at a specific frequency, we can realize the advantages of controlling the spatial frequency and temporal frequency (time-frequency), respectively. Fig. 3 shows the concept of thin-plate-type embedded MsT (TEMT). The transducer should have focused beam directivity pattern to obtain thickness information and should be able to endure in a high-temperature environment. 2.2. Analysis of acoustic field for the coil design Fig. 4 shows an analytical model of an SH bulk wave. To simplify the analysis, we used a two-dimensional harmonic analysis of a cross-section of the structure. Half-space field and point sources are also assumed when calculating the farfield responses. The response Rm due to point source Pm can be expressed as [19e21]:   rffiffiffiffiffiffiffiffiffiffiffiffi j 2pfrm þp cs 4 c s e Rm ¼ ð  1Þm p2 frm (1) where: rm ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 2 ðx  Xm Þ2 þ ð2hÞ (2) [rm: distance from Pm to the measurement point (x,2h)] when n is an odd number; Xm ¼ ðn  mÞd½1  n  ð2m  1Þ (3) when n is an even number; Xm ¼   2n  1  m dð1  n  2mÞ 2 (4) Fig. 2 e Schematic of the transducer component arrangement to excite and receive shear horizontal waves. Fig. 3 e Thickness gauge monitoring concept of a thinplate-type embedded magnetostrictive transducer. (Xm: the distance between the center O of the x  y coordinate system and Pm). In Eq. (1), cs denotes the shear wave velocity in an infinite medium and f is the frequency of the sources. In Eqs. (3) and (4), n is the total number of point sources, m is the total number of one-sided point sources due to half-modeling, and d denotes the distance between two adjacent point sources. To determine the coil design, we undertook a harmonic analysis using MATLAB. First, the frequency was assigned the very common value of 5 MHz. In addition, cs ¼ 3; 200 m=s was used for the calculation. Fig. 5 shows the calculated acoustic field of the proposed coil (d ¼ 0.6 mm) with five fingers (h ¼ 10 mm). According to the acoustic field in Fig. 5, the distance between the transmitter and the receiver was set to be 11.5 mm. The final coil design used in the present study is illustrated in Fig. 6. The copper coil was printed on a flexible printed circuit board (FPCB), making the coil flexible and applicable to object surfaces with various shapes. 2.3. High-temperature characteristics of TEMT components To install and drive a TEMT in a high-temperature environment, several major considerations must be made. The device is commonly composed of magnets (or electromagnets), magnetostrictive patches, and coils (see Figs. 1 or 2). Each component should be suitable in the target condition. Therefore, we studied their high-temperature characteristics as a preliminary study. Neodymium (Nd-Fe-B) magnets are universally used in various industrial products, showing good magnetic properties. They also have higher remanence and good coercivity and energy production. However, they have a lower maximum permissible temperature (250
C) than other permanent magnets. Accordingly, neodymium magnets are not appropriate here. Samariumecobalt (SmCo) and alnico (AleNieCo) magnets are possible alternatives because their Fig. 4 e Analysis model of the acoustic field of a shear horizontal bulk wave. N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 1407 Fig. 5 e Calculated acoustic field of the proposed coil with five fingers (f ¼ 5 MHz, d ¼ 0.6 mm, h ¼ 10 mm). maximum permissible temperatures are 350
C and 450e550
C, respectively. With regard to the magnetic properties, SmCo magnets are better than alnico magnets. FeCo alloy is one of best magnetostrictive materials, with a higher, and proper, Curie temperature of 940
C. This material is appropriate for the temperature range of this study. The amplitude of an SH wave on a FeCo alloy patch under a hightemperature condition was checked and compared with those of neodymium, SmCo, and alnico magnets [16]. The magnetostriction was acceptable at 300
C in both the SmCo and alnico magnets. However, the amplitude with the neodymium magnets collapsed at 250
C. We found that SmCo or alnico permanent magnets can create a bias magnetic field at the temperature range up to 300
C and an FeCo alloy patch can deform enough to transduce an SH wave efficiently. Magnetostriction depends heavily on the bias magnetic field; thus, we studied changes in the bias magnetic field due to temperature variations in detail and attempted to determine a proper and optimal magnetic field in the target condition. Fig. 7 shows a schematic of the experimental setup used to test the high-temperature characteristics of the TEMT. Current from a DC power supply can enable an electromagnet to produce a bias magnetic field. SH waves on an FeCo alloy patch are measured to observe the magnetostrictive deformation behavior. A sine burst wave of two cycles is transmitted and received in the pulse-echo method. Fig. 8 shows the measured signal of the SH wave, where Vpp is the difference between the values of the maximum and minimum amplitudes of the measured SH wave. The repeatability was checked and the hysteresis was verified to confirm uniform conversion efficiency. Fig. 6 e Design drawing of the meander coil on a flexible printed circuit board. Fig. 7 e Experimental arrangement used to test the hightemperature characteristics of a thin-plate-type embedded magnetostrictive transducer. The SH wave measurements were taken under an elevated electric current for different temperature conditions. Fig. 9A shows the characteristics of the bias magnetic fields for each temperature condition. With a condition of the electric current of approximately 230 mA, Vpp showed the highest result. With current lower than 230 mA, Vpp increases rapidly. By contrast, Vpp decreases steadily when current higher than 230 mA is transmitted. In this case, good performance was noted under a low magnetic field. These results indicate that small magnets can be applied in this work because there is no need for high magnetic fields. Fig. 9B shows the conversion efficiency of an SH wave with the present measurements at an elevated temperature. The amplitudes at 200
C, 300
C, and 400
C declined by 3%, 11%, and 24%, respectively. Thus, the signal measurements under a high-temperature condition were reasonable. 2.4. Fabrication of a TEMT There are several considerations when fabricating a TEMT. Most importantly, the transducer performance should be Fig. 8 e Measured shear horizontal wave propagating through a FeCo alloy patch. 1408 N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 Fig. 9 e Amplitude of the measured SH waves. (A) under the varied bias magnetic field, and (B) under the varied temperature. stable under general circumstances and under hightemperature conditions. Therefore, the selection of transducer components is very important because these components will strongly influence the sensitivity and performance of the transducer. In this study, we considered applicable and durable parts of a TEMT. A FeCo alloy patch (Hiperco 50 HS) was selected as the magnetostrictive patch in this study. It is composed of 0.01% carbon, 0.05% manganese, 0.05% silicon, 0.30% columbium/ niobium, 1.90% vanadium, and 48.75% cobalt. For the best performance of bias magnetic field in high-temperature condition, SmCo permanent magnets were used. The FPCB type of meander coil was used and the thickness of the coil is approximately 0.1 mm. This thin film coil can endure temperatures as high as 300
C. However, deformation of the coil can occur due to temperature variations. Accordingly, precautions such as transducer molding are required to fix the coil. To apply at higher temperatures, it may need a ceramic bobbin and a coil-protecting tube. An asbestos tube was used, as it can protect the wire from the heat. Long-term heat Fig. 10 e Design and fabrication of a thin-plate-type embedded magnetostrictive transducer (TEMT). (A) Schematic of a TEMT. (B) A prototype TEMT and its components. (C) A curved TEMT as a pipe specimen. exposure causes the tube to crumble when rubbing it by hand. However, the wire shape is retained. Thermocouple wire is another possibility, but its resistance is much higher than those of other wires. As a result, impedance matching between the transducer and equipment can be challenging, but it is not impossible. A soft soldering material (Speedsol, resin core solder) was also used. Its solidus temperature is approximately 295
C. In addition, it seldom melts at temperatures up to 400
C. A general brazing filler metal (Shin Young Metal BAg-2) with a solidus temperature of 605
C was also prepared as a backup. However, a brazing method cannot be applied to an FPCB because the torch can melt the thin film. A special coil design is necessary when using the brazing method. To attach a TEMT onto a metallic structure, high temperature glue is needed. Two adhesives were selected for N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 1409 Fig. 11 e Experimental setup of thickness measurement test using the thin-plate-type embedded magnetostrictive transducer. use here: J-B Weld Steel Reinforced Epoxy (< 315
C) and Aremco Ceramabond 571-L/P (< 1,760
C). Fig. 10A shows a schematic of the prototype TEMT. Fig. 10B is a photograph of the fabricated prototype TEMT and its components. Two FeCo alloy patches are welded onto a metal case of KS-STS304 (stainless steel). These two patches are used to transmit and receive the part that reduces the direct surface wave. These welded patches transform properly. The ceramic inner case prevents deformation of the coil and fixes all components inside the TEMT. The thickness of the TEMT was approximately 3 mm in this work. Reducing the size of the magnets can make the transducer much smaller and thinner. Fig. 10C shows a curved TEMT applicable to a pipe specimen with a specific curvature. 3. Thickness measurement tests using a TEMT After the TEMT was fabricated, three types of experiments were conducted. Fig. 11 shows the experimental setup of these tests to measure the thickness of the plate and pipe specimen. Preliminarily, we attempted to evaluate the high-temperature performance of the TEMT. A carbon steel plate 10 mm thick was inspected and the transducer was attached onto the specimen using ceramic epoxy (Aremco) and metal reinforced epoxy (J-B Weld). Figs. 12A and 12B show the measured raw signal of an SH bulk wave with the ceramic epoxy attached to the TEMT at room temperature and at 300
C, respectively. The amplitude is decreased by 50% and arrival time is increased by nearly 4%. We confirmed that the temperature affected the TEMT, but the signal itself at 300
C did not change after 24 hours Fig. 12C shows the raw signal of the SH bulk wave measured by the metal-reinforced epoxied TEMT at 300
C. The amplitude is only 10% of that of the ceramic epoxy. However, the signal is better than the ceramic epoxy according to the results of a signal analysis. The metal-reinforced epoxy is restricted in terms of its workable temperature, which is < 315
C. Subsequently, to evaluate the performance of the TEMT as a thickness gauge, we prepared two types of carbon steel specimens. A stepped specimen with thickness variations (thicknesses of 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, and 5 mm) and a thin-walled pipe of 9 mm thickness were utilized. Among them, Fig. 13 shows first arrival time variation of the SH bulk wave due to the change in the of plate wall thinning. All first arrival times of SH bulk waves were determined by the peak selection of the wave. From these result, the first arrival time is shortened when the thickness decreases. In short, we confirmed that the TEMT can measure the thickness of plates. Accordingly, we studied the performance of a TEMT to detect pipe wall thinning. Fig. 14 shows the measured thickness of thin-walled pipe according to the scanning method. The total length of the thin pipe wall was about 90 mm, and the thickness of the center position is approximately 4.5 mm (50% wall loss). In this result, there are a few errors with regard to the measured thickness. However, some measured points are quite precise, and the result shows a well-fitted thickness profile. 1410 N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 Fig. 13 e First arrival time variation of shear horizontal bulk wave due to thickness change of plate wall thinning. 4. Discussion In this work, a thin-plate type of an ultrasonic transducer based on magnetostriction was proposed and developed to monitor the thickness of NPP secondary piping systems in high-temperature environments. To do this, two requirements were considered and duly weighed. First, the transducer should be able to be inserted between a pipe and the pipe insulation. Thus, it has to be thin. The proposed transducer can satisfy the requirements because a thin MsT can easily be made. Second, the transducer must be able to withstand a high-temperature condition. Hence, the selected components of the proposed transducer were those that could tolerate such a condition. All things considered, the design was established and the transducer was fabricated and tested. A coil 5 MHz (diameter ¼ 0.6 mm) in size with five fingers was determined and the optimum receiving distance was set to 12 mm. The Fig. 12 e Raw signal of shear horizontal bulk wave. (A) Ceramic epoxy attached thin-plate-type embedded magnetostrictive transducer (TEMT) at room temperature. (B) Ceramic epoxy attached TEMT at 300
C. (C) Metal reinforced epoxy attached TEMT at 300
C after 24 hours. Fig. 14 e Measured thickness of a thin-walled pipe by the scanning method. N u c l e a r E n g i n e e r i n g a n d T e c h n o l o g y 4 8 ( 2 0 1 6 ) 1 4 0 4 e1 4 1 1 bias magnetic field was checked, and it was found to decrease by 11% at 300
C. For the fabrication of the transducer, a FeCo alloy patch, an SmCo permanent magnet, and a hightemperature epoxy adhesive were selected. Finally, we developed the transducer with a thickness of about 3 mm and termed it a TEMT. The amplitude of an SH bulk wave transduced by the TEMT was decreased by about 50%. However, the amplitude was retained for more than 24 hours. Finally, thickness gauges for a thin-walled plate and pipe were completed, and the results with these represented well-fitted thickness measurements. For future work, to quantify the thickness data, several measurements and databases will be essential. The TEMT should also be improved, especially with a new design that reduces the deformation of the coil. Lastly, to prove the durability of the TEMT, sufficient testing for a long period in a high-temperature environment will be necessary. [7] [8] [9] [10] [11] [12] Conflicts of interest All authors have no conflicts of interest to declare. Acknowledgments This paper was supported by the Ministry of Science, ICT & Future Planning. references [1] K.M. Hwang, C.K. Lee, Pipe Wall Thinning Management Life Cycle in Korea, KEPCO-E&C Report, 2014. [2] S.H. Lee, T.R. Kim, S.C. Jeon, K.M. Hwang, Thinned Pipe Management Program of Korean NPPs, Transactions of the 17th International Conference on Structural Mechanics in Reactor Technology (SMiRT 17), 2003. Paper # O04e2. [3] Z. Zhimin, L. Jinsong, Z. Hui, Nuclear Power Plants Secondary Circuit Piping Wall-thinning Management in China, Third International Conference on Nuclear Power Plant Life Management (PLiM), 2012. IAEA-CN-194e033P. [4] P.C. Wu, Erosion/corrosion-induced Pipe Wall Thinning in U.S. Nuclear Power Plants, U.S. Nuclear Regulatory Commission Report, 1989. NUREG-1344. [5] R. Kazys, A. Voleisis, B. Voleisiene, High temperature ultrasonic transducers: review, Ultragarsas (Ultrasound) 63 (2008) 7e17. [6] M. Budimir, A. Mohimi, C. Selcuk, T. Gan, High Temperature NDE Ultrasound Transducers for Condition Monitoring of [13] [14] [15] [16] [17] [18] [19] [20] [21] 1411 Superheated Steam Pipes in Nuclear Power plants, 20th International Conference of Nuclear Energy for New Europe, 2011, pp. 502.1e502.8. X. Jiang, K. Kim, S. Zhang, J. Johnson, G. Salazar, Review: high-temperature piezoelectric sensing, Sensors 14 (2014) 144e169. R.T. Nisbet, Ultrasonic thickness measurements at high temperatures, NDT Tech. 3 (2004) 1e3. F.B. Cegla, P. Cawley, J. Allin, J. Davies, High-temperature (>500
C) wall thickness monitoring using dry-coupled ultrasonic waveguide transducers, IEEE Trans. Ultrasonics Ferroelectrics Freq. Cont. 58e1 (2011) 156e167. F.B. Cegla, A.J.C. Jarvis, J.O. Davies, High temperature ultrasonic crack monitoring using SH waves, NDT&E Int. 44 (2011) 669e679. F.B. Cegla, High Temperature Ultrasonic Monitoring with Permanently Installed Sensors, Proceedings of the National Seminar & Exhibition on Non-destructive Evaluation, 2011, pp. 360e363. F. Hernandez-Valle, S. Dixon, Initial tests for designing a high temperature EMAT with pulsed electromagnet, NDT&E Int. 43 (2010) 171e175. F. Hernandez-Valle, S. Dixon, Preliminary Tests to Design an EMAT with Pulsed Electromagnet for High Temperature, AIP Conference Proceedings 1096, 2009, pp. 936e941. A.J. Ashish, P. Rajagopal, K. Balasubramaniam, A. Kumar, B.P. Rao, T. Jayakumar, Development of Magnetostriction Based Ultrasonic Transducer for in-situ High Temperature Inspection, NDE-2015, 2015. R.S. Sundar, S.C. Deevi, Soft magnetic FeCo alloys: alloy development, processing, and properties, Int. Mater. Rev. 50e3 (2005) 157e192. T. Heo, J. Park, B. Ahn, S.H. Cho, The feasibility study on a high-temperature application of the Magnetostrictive transducer employing a thin Fe-Co alloy patch, J. Korean Soc. Nondestructive Testing 31 (2011) 278e286. Y.Y. Kim, Y.E. Kwon, Review of magnetostrictive patch transducers and applications in ultrasonic nondestructive testing of waveguides, Ultrasonics 62 (2015) 3e19. G. Hubschen, UT with SH-waves and electromagnetic ultrasonic (EMUS) -transducers, Rev. Prog. Quant. Nondestruct. Eval. 9 (1990) 815e822. M. Spies, Computationally efficient SH-wave modeling in transversely isotropic media, J. Nondestruct. Eval. 19 (2000) 43e54. S.H. Cho, J.S. Lee, Y.Y. Kim, Guided wave transduction experiment using a circular magnetostrictive patch and a figure-of-eight coil in nonferromagnetic plates, Appl. Phys. Lett. 88 (2006) 224101. J.S. Lee, Y.Y. Kim, S.H. Cho, Beam-focused shear-horizontal wave generation in a plate by a circular magnetostrictive patch transducer employing a planar solenoid array, Smart Mater. Struct. 18 (2009) 015009.