achievable with a Hall probe by at least a factor of ten. Finite element design optimization of the read head and shield are described. These give a signal amplitude dependent on defect penetration but essentially independent of defect width. Test results are given.
38248 Kalwa, E.; Piekarski, K. Design of inductive sensors for magnetic testing of steel ropes NDT International, Vol. 20, No. 6, pp. 347-353 (Dec. 1987)
The design and operating principles of four inductive sensors for magnetic testing of steel ropes are presented. The magnetic concentrators can maintain the same shape as in Hall-effect leakage flux sensors, but the output signals of the inductive sensors am quite different and depend on the speed of testing. Although the inductive sensors are not as versatile as Hall-effect sensors, they are simpler in operation and can still find applications, especially in the initial and middle stages of the deterioration of the rope.
38237 Kalwa, E.; Piekarskz', K. Design of Hall-effect sensors for magnetic testing of steel ropes NDT International, Vol. 20, No. 5, pp. 295-301 (Oct. 1987)
The design and operating principles of four new Hall-effect sensors for magnetic testing of steel ropes are presented. The radial or tangential component of the magnetic leakage flux can be measured efficiently depending on the shape of the concentrators (rings or sleeves). The output signal can be modified by using multiple constructions of the basic sensors. Different sensors can he used depending on the predominant character of the wear of the rope.
37629 Atherton, D.L.; Czura, W. Finite element calculations on the effects of permeability variation on magnetic flux leakage signals NDT International, Vol. 20, No. 4, pp. 239-241 (Aug. 1987)
Magnetic flux leakage anomaly signals from pipeline inspection tools can be obtained from hard spots or other regions of anomalous permeability. The signals obtained from corrosion pits am dependent on pressure and this is atU'ibuted to stress-induced permeability changes. The results of two-dimensional finite element calculations of the effects of permeability measurements on such signals suggest that permeability changes by as much as a factor of two may be required to produce these effects.
37628 Atherton, D.L.; Daly, M.G. Finite element calculation of magnetic flux leakage detector signals NDT International, Vol. 20, No. 4, pp. 235-238 (Aug. 1987)
Two-dimensional finite element calculations are presented for anomalous leakage fluxes generated by nearside and farside grooves in pipes inspected by magnetic flux leakage anomaly detectors. Flux density (B) is shown to be a non-linear function of penetration, increasing rapidly for deep grooves. This is contrary to previous analyses of cracks or grooves in plates using constant-field (H) excitation. The difference is due to the inclusion of the anomaly detector assembly which tends to act with constant flux, particularly for detectors excited by permanent magnets. The new results are therefore of greater practical relevance.
37167 Fujinaka, Y.; Hanasaki, K.; Tsukada, K. Magnetic inspection of P.W.S. ropes I I th World Conference on Nondestructive Testing, Las Vegas, Nevada (United States), 3-8 Nov. 1985. Vol. I, pp. 154-161. Taylor Publishing Co., Dallas (1985).
A leakage magnetic flux method was used to evaluate the deterioration of Parallel Wire Strand (P.W.$.) suspension cables. A method is developed for estimating the residual strength of a corroded P.W.S. due to loss in the cross section area obtained by inspection records.
37166 Fitzpatrick, G.L. Imaging near-surface flaws in ferromagnetic materials using magneto- optic detectors l l th World Conference on Nondestructive Testing, Las Vegas, Nevada (United States), 3-8 Nov. 1985. Vol. 1, pp. 186-191. Taylor Publishing Co., Dallas (1985).
A new method for direct, instantaneous viewing of near-surface flaws in ferromagnetic materials has been developed. By using special magnetic garnet films (a magneto-optic material), it is possible to make the magnetic fields associated with near-surface flaws visible. Moreover, by pro~dy biasing the magnetic garnet film with an external magnetic field, these images can reproduce the size and shape of the flaws. In many applications the new viewing method can replace conventional magnetic particle or flux leakage inspection techniques. The new viewing method appears to be especially well suited to production line applications where minimal sample
ND T Abstracts
preparation and rapid inspection are basic requirements. Because the magnetic garnet film responds to fields associated with eddy currents, the method may be applicable to nonmagnetic conductors.
37163 Qi, Z.; Lunyuan, Y. Near crack in ferromagnetic materials for magnetic NDT 1 lth World Conference on Nondestructive Testing, Las Vegas, Nevada (United States), 3-8 Nov. 1985. Vol. 1, pp. 216-225. Taylor Publishing Co., Dallas (1985).
A mathematical model of magnetic testing is proposed after analysis of the leakage field producing mechanism. A finite element method is applied to solve nonlinear magnetic leakage field problems. Analyses and calculations are made on the dislribution of the leakage field near cracks in ferromagnetic materials. The leakage flux caused by artificial cracks was measured by means of a Ganssmeter with a Hall probe. Values calculated using the model correspond to experimental results.
37159 Spierer ED. Flux density measurement in ferromagnetic tubu la r product Electromagnetic Methods of Nondestructive Testing. Edited by William Lord. Nondestructive Testing Monographs and Tracts, Vol. 3, pp. 161- 173. Gordon and Breach Science Publishers (1985).
Flux leakage testing of ferromagnetic tubular product for defects requires that the flux density in such product be near 95% of saturation when being tested. If the flux density in the material under test is significantly below saturation, inside-diameter and mid- wall defects will be missed. Until recently there has been no means of determining the value of the flux density in the tubular product or whether this value is maintained during testing in order to validate the test. This paper presents a solution to the problem of continuous determination of the flux density in the material under test.
37157 Stanley, R.K. Basic principles of magnetic flux leakage inspection systems for the evaluation of oil country tubu la r goods Electromagnetic Methods of Nondestructive Testing. Edited by William Lord. Nondestructive Testing Monographs and Tracts, Vol. 3, pp. 97- 149. Gordon and Breach Science Publishers (1985).
This article attempts to elucidate some of the scientific principles behind the magnetic aspects of the inspection of ferromagnetic oil country tubular goods (OCTGs). Following an overview of flux leakage inspection methods, a section which outlines how the physical principles which govern magnetism and magnetic flux leakage are related to pipe inspection is presented. The article concludes with several examples of defect detection by magnetic flux leakage, and some examples of non-relevant indications arc also discussed.
37156 Dobmann, G. Magnetic leakage flux techniques in NDT a state-of-the-art survey of capabifities for defect detection and sizing Electromagnetic Methods of Nondestructive Testing. Edited by WiUiam Lord. Nondestructive Testing Monographs and Tracts, Vol. 3, pp. 71- 95. Gordon and Breach Science Publishers (1985).
This paper discusses several magnetic leakage flux techniques in NDT. Problems encountered in magnetic particle inspection, magnetic probe testing, and magnetography i.e., the use of a magnetic-tape to store the magnetic leakage fields during magnetization, are outlined.
37155 Bergander, M.I. Magnetic flux leakage inspection of wire rope Electromagnetic Methods of Nondestructive Testing. Edited by William Lord. Nondestructive Testing Monographs and Tracts, Vol. 3, pp. 21- 33. Gordon and Breach Science Publishers (1985).
Steel wire ropes used in a wide variety of men and material handling equipment are subjected during their operation to internal and external factors, which normally result in a progressive loss of strength and service life. This loss can be attributed to several different damage mechanisms e.g. fatigue, corrosion, wear, etc. The problem of accurate and relatively fast methods for wire rope inspection becomes very important due to both safety and economical reasons. The failure to discard the old rope at the proper time may even cause its catustrophic breakage
36895 Huschelrath, G.; Schneider, P. New applications of the computerized mul t iprobe flux leakage test system STAR Proceedings of the 9th Congress of Materials Testing, Budapest (Hungary), 29 Sep. - 3 Oct. 1986. Vol.2. pp. 616-617. Edited by E. Czoboly. Scientific Society of Mechanical Engineers (1986).
NDT&E International Volume 26 Number 1 1993 41