The present paper introduces an application of the acoustic and thermographic method in the defectoscopic testing of immobile steel wire ropes at the most critical point, the anchor. First measurements and their results by these new defectoscopic methods are shown. In defectoscopic tests at the anchor, the widely used magnetic method gives unreliable results, and therefore presents a problem for steel wire defectoscopy. Application of the two new methods in the steel wire defectoscopy at the anchor point will enable increased safety measures at the anchor of steel wire ropes in bridge, roof, tower and aerial cable lift constructions.U ovom prilogu predstavlja se primjena jedne akustičke i termografske metode u defektoskopskom ispitivanju nepokretnih čeličnih žičanih kablova na najkritičnijoj točki, na sidru. Najprije su prikazana mjerenja i njihovi rezultati dobiveni tim novim defektoskopskim metodama. U defektoskopskim ispitivanjima na sidru naširoko korištena magnetska metoda pruža nepouzdane rezultate te stoga predstavlja problem za defektoskopiju čelične žice. Primjena dviju novih metoda u defektoskopiji čelične žice na točki sidra omogućit će uporabu mjera veće sigurnosti na sidru čeličnih žičanih kablova u konstrukcijama mostova, krovova, tornjeva, žičara

J. Krešák

P. Peterka

S. Kropuch

English

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485METALURGIJA 51 (2012) 4, 485-488J. KREŠÁK, S. KROPUCH, P. PETERKATHE ANCHORS OF STEEL WIRE ROPES, TESTING METHODS AND THEIR RESULTSReceived – Prispjelo: 2011-12-15Accepted – Prihvaćeno: 2012-03-20Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 51(4) 485-488 (2012)UDC – UDK 669.14-418:539.37:620.17=111The present paper introduces an application of the acoustic and thermographic method in the defectoscopic test-ing of immobile steel wire ropes at the most critical point, the anchor. First measurements and their results by these new defectoscopic methods are shown. In defectoscopic tests at the anchor, the widely used magnetic method gives unreliable results, and therefore presents a problem for steel wire defectoscopy. Application of the two new methods in the steel wire defectoscopy at the anchor point will enable increased safety measures at the anchor of steel wire ropes in bridge, roof, tower and aerial cable lift constructions. Key words: nondestructive testing (NDT), wire ropes, thermography, defectoscopySidra čeličnih žičanih kabela, metode ispitivanja i njihovi rezultati. U ovom prilogu predstavlja se primjena jedne akustičke i termografske metode u defektoskopskom ispitivanju nepokretnih čeličnih žičanih kablova na najkritičnijoj točki, na sidru. Najprije su prikazana mjerenja i njihovi rezultati dobiveni tim novim defektoskopskim metodama. U defektoskopskim ispitivanjima na sidru naširoko korištena magnetska metoda pruža nepouzdane rezultate te stoga predstavlja problem za defektoskopiju čelične žice. Primjena dviju novih metoda u defektoskopiji čelične žice na točki sidra omogućit će uporabu mjera veće sigurnosti na sidru čeličnih žičanih kablova u konstruk-cijama mostova, krovova, tornjeva, žičara.Ključne riječi: ispitivanje bez razaranja (IBR), žičani kablovi, termografi ja, defektoskopijaINTRODUCTIONAt present, there is a great boom in development of technologies, which puts a large emphasis on quality, reliability, life expectancy and effectiveness of prod-ucts, devices and machinery. At the same time, there is a great demand to save energy, raw materials, and main-tenance and qualifi ed labor costs in the manufacturing process. NDT gains an important role in the evaluation of quality and reliability of products, together with sav-ing energy and maintenance costs of machinery already used in production. Defectoscopy also becomes a sig-nifi cant part of entrance quality inspection of incoming raw materials, and in checkout quality tests of produc-tion. We use several methods. Our laboratory has intro-duced magnetic, acustic and thermographic methods for detecting cracks on steel wire ropes in our laboratory. The aim of the article is to present the possible way for detecting cracks in the area of anchorage of the steel wire ropes. Defectoscopic devices for testing of steel wire ropes use a principle of magnetic fl ux leakage (magnetic method). The scattering of the primary magnetic fl ux depends on a size, shape and position of the non-homo-J. Krešák, S. Kropuch, P. Peterka, Faculty of Mining, Ecology, Process Control and Geotechnology, Technical University of Košice, Košice, Slo-vak Republic.geneity in a tested sample. Further, it also depends on a value of magnetic induction by which the sample was magnetized. The highest degree of scattering of the magnetic fl ux occurs at the surface non-homogeneity point located perpendicularly to the direction of the magnetic fl ux. In order to apply the magnetic method correctly, it is necessary to measure the above-men-tioned magnetic characteristics of a tested sample, to choose the appropriate method of magnetization, and to determine whether the sample was magnetized to a suf-fi cient degree[1]. Destructive tests as well as above mentioned nonde-structive magnetic defectoscopic method for the evalu-ation of steel wire rope quality and safety characteristics are frequently used. Due to a doubtful signal from the magnetic and other defectoscopic methods at the anchor points, we were compelled to develop a new nonde-structive defectoscopic method and device for testing of anchored steel wire ropes at the anchor. We developed a new acoustic defectoscopic method by which it is possible to measure a change in diameter of steel wire rope within proximity of and at the anchor. We modifi ed a method for measurement of an elasticity modulus of steel wire ropes by means of acoustic vibra-tion [2 - 4]. At present, the method that monitors a temperature change within objects is widely used for the purposes of testing the electrical equipment and machinery. The 486  METALURGIJA 51 (2012) 4, 485-488J. KREŠÁK et al.: THE ANCHORS OF STEEL WIRE ROPES, TESTING METHODS AND THEIR RESULTSmethod is known as thermovision. All objects emit pho-tons within the infrared range of the spectra, and the number of the emitted photons depends on object’s tem-perature. This relationship can be used for visible repre-sentation of a thermal fi eld radiated by the surface of observed objects. The thermograhic method has a uni-versal use, and is based on a transformation of infrared radiation into a visible spectrum. The measurement is contactless. The optical system registers emitted infra-red photons from the observed object and conveys them to the detector, where the energy of the photons is trans-formed into electrical signals. The electrical signals are multiplied and used for the regulation of emission of electrons in an ordinary television screen [5-8].EXPERIMENTS AND DISCUSSIONNDT testing of loose wire ropes segments uses rou-tinely above-mentioned magnetic method. The method gives very good results, which are reliable and repro-ducible, especially with use of attached sensory coils and Hall’s sensors. The problems arise when this meth-od is used to test immobile steel wire ropes anchoring bridge, roof or other constructions and drilling towers [1]. The greatest challenge arises during defectoscopic test of immobile steel wire rope at its anchor point. Due to rope anchoring, the diameter and profi le of the rope suddenly change Figure 1, and this discrete transition represents obstacle for classic defectoscopic method. Magnetization and movement of attached sensory coil or Hall’s sensor at the anchor point are diffi cult, and therefore defectoscopic measurements taken at this point are doubtful [1]. Based on our experience with the method of the scattering of the primary magnetic fl ux, we can conclude that this method gives false positive signals (irrelevant indications) at the anchor point as in-dicated in Figure 1[1]. During development of the appropriate conditions in application of acoustic defectoscopic method, we used assumption that by direct measurements of the tension force F, mass density ρ, wire rope prolongation ∆lσ, and original length of rope l1 we will be able to obtain a real value of steel wire rope cross-section. Figure 2 shows dependence of the measured cross-section value from the tractive force of unperturbed rope and ropes with various numbers of perturbed wires. Measurements were obtained for steel wire rope type 6x(1+12+18) ac-cording standard STN 02 4324.41, i. e. a rope consisted of 222 zinc plated wires. The rope was twisted in alter-nate lay and its diameter was 16 mm. According stand-ard STN EN 12 385, this rope type is d 16 1570 FS sZ. Blue line shows dependence of the cross-section from the tension force in unperturbed steel wire rope. This calculated cross-section based on above measured pa-rameters should correspond with cross-section value from manufacturer. Moreover, dependence should not decrease with increasing force, because the cross-sec-tion had a same value in three measurements at F of 12 500 N, 18 000 N, and 24 000 N, respectively. It is clear that according to results in Figure 2, the cross-section value decreases with increasing tension force. Discrep-ancy between cross-section calculated value and value from manufacturer points out an error in measurements of the input parameters for the tension force F, mass density ρ, wire rope prolongation ∆lσ, and velocity of propagation of sound in the rope √. Following lines shows dependence of the cross-section from the tension force in steel wire rope containing perturbed wires: ma-genta line 30 perturbed wires, yellow 42 perturbed wires, and cyan 55 perturbed wires. The profi le of dependences measured from ropes with perturbed wires is similar to the dependence measured from unperturbed rope, decrease of cross-section value with the increasing tension force. This further indicates the inaccuracy in measurements of input parameters. 2345dDh1Figure 1  Rise of irrelevant indications within steel wire rope at the anchor. 1 is a conical cable end, 2 is a steel wire rope, 3 is a magnetic yoke, 4 is a point where irrelevant indication arises, 5 represents magnetic fl ux force lines.506070809010011010 000 15 000 20 000 25 000 Tension force / NCross-section / mm20 breaks 30 breaks42 breaks 55 breaksFigure 2 Dependence of the measured cross-section from the tension force in the unperturbed rope and ropes with various numbers of perturbed wires. Tension force F applied along the wire axis is on x axis, and cross-section obtained by acoustic method is on y axis. The value of cross-section was calculated from Eq. 4 with use of the measured values of parameters by acoustic method, the tension force F, mass density ρ, wire rope prolongation ∆lσ, and velocity of propagation of sound in the rope √. 487METALURGIJA 51 (2012) 4, 485-488J. KREŠÁK et al.: THE ANCHORS OF STEEL WIRE ROPES, TESTING METHODS AND THEIR RESULTSTaking together, the measured results and equations describing acoustic method, it is clear that to obtain re-producible results in repetitive measurements, we have to measure with higher accuracy the input parameters: initial length of the rope section, tension force in the rope and the velocity of sound propagation in the rope. Then, based on accurate above-mentioned input param-eters, value of a mass density and a coeffi cient of ther-mal extensibility, we can accurately determine cross-section of the rope in a section of interest. The velocity of acoustic wave propagation within the wire steel rope is detected by sensors attached to the rope. A stroke force is developed by a pendulum con-sisting of a ball, angle-measuring instrument and mag-netic support stand. The pendulum creates a reproduci-ble mechanical stimulus in the steel wire rope with the same characteristics in repetitive experiments. The ten-sion force in the tested rope is measured by a cylindrical sensor containing four tensometers. Set up for measure-ment input parameters by acoustic method is showed in Figures 3, 4.By the acoustic measuremens applied on the steel wire ropes thermographic tests of the ropes were done as well. This method was used in experiments with sus-pended load with a loop. Specimens were fastened be-tween the bolts of the testing device, which corresponds to the way of fastening fi xed load-carrying anchor ropes to various constructions. Figure 5 shows relationship between an increase of temperature in the cross-section of a perturbed steel rope and safety coeffi cient, i.e. de-pendence on the value of the tension force. With the decreasing safety coeffi cient value of the tension force increases, for example tension force is greater at the safety coeffi cient of 2 than at the coeffi cient of 4,5. Dis-played relationship in fi gure 5 clearly indicates that with the increasing tension force, or decreasing safety coef-fi cient, temperature in the rope cross-section increases. Increase in temperature is gradual until safety coeffi -cient of 2,5. The increase becomes quite steep at the coeffi cients with value < 2,5. Figures 6, 7 displays a thermal fi eld of steel wire rope sample after rupture.CONCLUSIONSBased on the results in testing of steel wire ropes at anchor obtained by means of acoustic method and ther-movision in our laboratory, it is possible to conclude that both methods can reliably detect defects. To im-Figure 3 Acoustic method measurement set up. Acoustic analysis part of the set up. Figure 4  Acoustic method measurement set up. Display of the measurement part of the set up – microphones and deviation gauger. y = -0,4774x 3 + 4,4294x 2 - 12,94x + 26,973R2 = 0,64611414,51515,51616,51717,51818,5190 1 2 3 4 5Safety coefficientTemperature / °CtemperaturePolynomic profileFigure 6  Ruptured steel wire rope. Thermogram – transformed infrared fi eld into visible spectra. Figure 5  Relationship between temperature and safety coeffi  cient in sample. Safety coeffi  cient is on x axis, and measured temperature by thermographic method is on y axis.488  METALURGIJA 51 (2012) 4, 485-488J. KREŠÁK et al.: THE ANCHORS OF STEEL WIRE ROPES, TESTING METHODS AND THEIR RESULTSFigure 7  Ruptured steel wire rope. Same rope (fi gure 6) in visible light.prove application of both methods, it is necessary to do measurements in the various weather conditions. This will be an aim of a research project in near future. Pre-liminary results indicate that increased tension in the tested sample results in increased temperature and also in faster propagation of an acoustic signal. Present re-sults show that the acoustic method gives reliable infor-mation about relative change in the cross-section of steel wire rope under different tension forces, however initial determination of cross-section is inaccurate. As all defectoscopic methods, the acoustic method is rela-tive, and thus it is necessary to do initial measurements of the tested section when there is no damage. Accord-ing results in fi gure 2, cross-section decreases with in-creasing tension force. Discrepancy between cross-sec-tion calculated value and value given by manufacturer indicates an error in measurements of the input param-eters: tension force in the rope, mass density, velocity of acoustic signal, and length change of the rope section. Therefore it is necessary to improve accuracy in meas-urements of input parameters. Results obtained by ther-mographic method indicate that it is necessary to im-prove sensitivity of this method as the change in the temperature is gradual in a wide range of the safety co-effi cients and signifi cant change arises with coeffi cient of 2 or less, when damage of the rope is critical and near rupture. Therefore, at the moment, thermovision is use-ful for determining already critically damaged ropes. It can be used as one of the method for diagnostic of the technical properties of steel wire ropes at the anchor points.AcknowledgementsSupported by the Scientifi c Grant Agency (VEGA) of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences, grant no. VEGA 1/0962/11.REFERENCES[1]  P. Peterka, J. Krešák, S. Kropuch, Non-destructive tests of the steel wire ropes. Metalurgija. 43, (2004)4, 343-344.[2]  E. Štroffek, I. Leššo, Acoustic method for measurement of Young s modulus of steel wire ropes., Metalurgija. 40(2001)4, 219-221.[3]  I. Leššo, P. Flegner, B. Pandula, P. Horovčák, New princi-ples of process control in geotechnics by acoustic methods. In: Metalurgija. 46(2007)3, 165-168. [4]  T. Bugár, Vibrodiagnostické skúšky oceľových lán In: NDT Welding Bulletin. 17(2007)2, 55-57. [5]  X.P.V. Maldague, Theory and practice of infrared techno-logy for nondestructive testing. New York: Wiley; 2001.[6]  Heriansyah, R., Abu-Bakar, S.A.R.: Defect detection in thermal image for nondestructive evaluation of petroche-mical equipments. NDT and E International 42 (8), pp. 729-740 2009 [7]  Gonzalez RC,Woods RE. Digital image processing, 2nd ed. Upper Saddle River, New Jersey: Prentice-Hall, Inc.; 2002.[8]  Ng HF. Automatic thresholding for defect detection. Pat-tern Recognition Letters 2006;27:1644–9.Note:  The responsible for English language are Katarína Štroffeková, Kurt Magsamen and Viera Nemčoková, Košice, Slovakia

Sidra čeličnih žičanih kabela, metode ispitivanja i njihovi rezultati

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