EP1076821A1 - Procede et appareil non destructifs et en ligne de determination des proprietes mecaniques de cables en acier inoxydable - Google Patents

Procede et appareil non destructifs et en ligne de determination des proprietes mecaniques de cables en acier inoxydable

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Publication number
EP1076821A1
EP1076821A1 EP99910640A EP99910640A EP1076821A1 EP 1076821 A1 EP1076821 A1 EP 1076821A1 EP 99910640 A EP99910640 A EP 99910640A EP 99910640 A EP99910640 A EP 99910640A EP 1076821 A1 EP1076821 A1 EP 1076821A1
Authority
EP
European Patent Office
Prior art keywords
cable
tested
phase
readings
ratio
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP99910640A
Other languages
German (de)
English (en)
Inventor
Mordechai Melamud
Gabriel Kohn
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Case Technologies Ltd
Original Assignee
Case Technologies Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Case Technologies Ltd filed Critical Case Technologies Ltd
Publication of EP1076821A1 publication Critical patent/EP1076821A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
    • G01N27/725—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables by using magneto-acoustical effects or the Barkhausen effect

Definitions

  • This invention relates to the measurement of the mechanical properties of stainless steel (hereinafter, briefly, SS) cables and particularly to determining failures in the mechanical properties of such cables due to stress in use, and to detecting fatigue damage that might cause failure of the cables.
  • SS stainless steel
  • US 5,619,135, of April 8, 1997 discloses a steel hardness measurement system and method of using the same for measuring at least one mechanical or magnetic characteristic of a ferromagnetic sample as a function of at least one magnetic characteristic of the sample.
  • the steel sample is preferably rolled sheet steel, i.e., steel having a thickness of approximately 2 mm or less.
  • Said patent provides means for testing only a sample of the sheet, but, in order to test a significant part of its surface area, a very large number of sensors is required.
  • a complete test of sheets is not practical according to US 5,619,135, as it mainly relates to the testing of stationary steel sheet samples; and the tests of steel structures other than steel sheets is not considered therein.
  • PCT application WO 98/20335 describes and claims a method for measuring the mechanical properties of ferromagnetic, elongated structures, particularly cables, which comprises the following steps: - creating at least a magnetic field that varies either as a function of time or the function of position or both, along at least a given length of ⁇ cable;
  • the aforesaid PCT application also describes and claims an apparatus for measuring the mechanical properties of elongated, ferromagnetic structures, particularly cables, which comprises means for generating a magnetic field that varies along at least a given length of the elongated structure; a plurality of Barkhausen Signal sensors distributed along said structure length; and means for comparing the signals relative to each section of the structure to be tested.
  • the austenitic stainless steels are composed of mostly a non-magnetic phase called austenite with minor quantities of magnetic phases like ⁇ ferrite or ⁇ and ⁇ 1 martensite.
  • the austenite in these steels is not a completely stable phase and transforms under certain conditions - low temperature or mechanical (plastic) .deformation - to the more stable phase, martensite, which is a ferromagnetic phase, whereas the austenitic phase is paramagnetic. This transformation has been documented in the literature, see e.g. Hecker, M.G. Stout, K.P. Staudhammer, and J.L.
  • Stainless steel wire ropes are manufactured using either cold or hot drawing techniques. In either case, the product contains varying, but small, amounts of a magnetic phase.
  • a typical Barkhausen Signal (hereinafter, briefly, "BS") from a typical AISI 302 SS wire is presented in Fig. 1. Subjecting the wire to external loads will cause a phase transformation which will lead to the formation of martensite, i.e., more magnetic phase will be present in the microstructure of the cable. It is a well established fact that deformation induced martensite significantly enhances strength generated by cold work.
  • the amount of martensite in the material can be monitored using existing laboratory equipment (e.g., the Ferritoscope) with low accuracy. This measurement is performed off-line, on a small sample, and is destructive, because a sample has to be taken from the cable or the wire.
  • This invention provides a method and apparatus for determining the mechanical properties of SS cables or wires, especially of the AISI 3XX type, that is applicable on line, both in production and in use.
  • AISI 3XX type AISI 3XX type
  • the method according to the invention comprises comparing the amount of martensitic phase induced by strain to the amount of the original magnetic phase in the cable being tested.
  • the original magnetic phase is determined by taking out a baseline reading of the BS for a master cable.
  • the master cable is the same cable to be tested, but as it was when new, either prior to or right after installing the cable in service, or is an equivalent cable.
  • Said baseline reading can be called "BS calibration”.
  • Equivalent cable is meant herein a cable which is sufficiently similar to the cable being tested as to give essentially the same baseline reading that this latter would have given when new.
  • a cable obtained from the same production hne from which the cable to be tested has been obtained, is in general a satisfactory equivalent cable.
  • the amount of martensitic phase induced by strain is determined, preferably at regular intervals and at any rate whenever the cable is to be tested, by taking out a successive reading or readings of the BS of said cable.
  • the comparison of the amount of martensitic phase induced by strain to the amount of the original magnetic phase is effected by determining a first value of a parameter which represents the amount of martensitic phase induced by strain to a second value of the same parameter which represents the amount of the original magnetic phase, and determining the ratio of said two values.
  • Said parameter will be called hereinafter “phase parameter” (hereinafter sometimes abbreviated as Pp) and their ratio will be called “the martensite index”.
  • the martensite index may be: a) the ratio R between the two area integrals relating correspondingly to the two peaks obtained the two relevant BS readings (viz.
  • the chosen martensite index is related to the number of fatigue cycles. This can be done by submitting a master cable, as hereinbefore defined, to a number of fatigue cycles up to its failure, and determining the martensite index at successive numbers of fatigue cycles.
  • a diagram - hereinafter, "the fatigue diagram" - can thus be constructed having the number of fatigue cycles as a first coordinate (e.g. the abscissa in Fig. 3) and the martensite index as the other coordinate.
  • the other coordinate will indicate the number of fatigue cycles that the cable has been submitted to, and will show how far it is from failure.
  • Fig. 1 is a BS diagram of a section of a new AISI 302 cable
  • Fig. 2 is a BS diagram of the same section of cable after a few cycles of fatigue (i.e., bending);
  • Fig. 3 is a diagram illustrating the variations of the martensite index
  • Figs. 4a, 4b and 4c schematically illustrate an embodiment of apparatus for carrying out the invention
  • Fig. 5 schematically illustrates another embodiment of said apparatus
  • Fig. 6 is a block diagram illustrating the method and the apparatus according to an embodiment of the invention.
  • the inventors have found that stressing a SS wire or cable (i.e. an AISI 302 wire) to low cycle fatigue by bending not only dramatically increases the amount of magnetic (martensitic) phase in the wire, but causes concurrent changes in the BS from the cable which can be quantitatively related to the cable's strength or to the expected remaining life of the cable.
  • a SS wire or cable i.e. an AISI 302 wire
  • FIG. 1 depicts the measured number of BS as a function of applied magnetic field as measured for a new cable made of AISI 302 SS.
  • Fig. 2 depicts the results for the same cable after it has been subjected to about 90 cycles of fatigue, in which the measurement of the BS was taken at the point subjected to the fatigue; while at any other point of the cable, the result was similar to that shown in Fig. 1.
  • Barkhausen Signals of the tested cable can be measured in any suitable way, and particularly in any one of the ways described in said WO 98/20335. For the sake of illustration, one such apparatus and method will now be described
  • the magnetic field, which generates the BS may vary either as function of time, as a function of position, or as a function of both.
  • a device for measuring the field strength such as a Hall probe can be used.
  • the field can be produced by at least an electromagnet fed with an alternating current, at least a sensor being provided in a fixed position with respect to the electromagnet, the cable being stationary or moving with respect to the apparatus unit constituted by the electromagnet and the sensor, and the time (or cable speed of movement), with respect to which the BS is measured, being recorded.
  • the apparatus comprises a number of permanent magnets 10. They are at least two, they fully encircle the cable (not shown) and are magnetized parallel to their axis. They are arranged along the path of the tested cable (not shown) with opposing magnetic poles facing each other, as designated by S and N in the drawing.
  • a few Barkhausen sensors 11 are spaced equally between the magnets along the axis of the apparatus, viz. the tested cable path, at positions of known, predetermined values of the applied magnetic field.
  • the magnets are split so that it is possible to open the apparatus, consisting of two halves 13, in order to encircle the tested cable.
  • a Relative Cable-Sensor Speed (RCSS) measuring unit 14 is placed inside the apparatus housing to measure the speed of the cable relative to the sensor. Both the magnets and sensors are mounted on adjustable mounts so as to fit various cable diameters.
  • RCSS Relative Cable-Sensor Speed
  • FIG. 5 Another apparatus, slightly different from the previous one, is schematically shown in Fig. 5. It contains at least two DC electromagnets 20, Barkhausen sensors 21, and RCSS 22, mounted on a casing 23. This apparatus cannot be opened SQ, as to be mounted around a cable, and is therefore intended to be used on the production line of wire ropes (not shown), or at any other installation where the tested wire rope can be inserted through the apparatus.
  • the apparatus used in carrying out this invention therefore, comprises:
  • memory means for storing said parameters measured on the new or equivalent cable and on the cable to be tested, referred to the conditions under which they have been measured; means for calculating the martensite index; and means for calculating the number of fatigue cycles that a tested cable has undergone.
  • the master cable or the tested cable are sensed, as indicated at 30 and 31 respectively, in an apparatus 32 to determine the Barkhausen signals.
  • Numeral 33 generally indicates computer means, to which the BS are transmitted. The computer means 33 calculates from the transmitted BS the phase parameters (chosen among the various Pp that may be used, as hereinbefore set forth) of the master cable or ihe tested cable, as the case may be.
  • the variations of the chosen Pp are due only to fatigue cycles to which the master cable has been deliberately submitted, and the fatigue cycle counts are inputted into the computer, as indicated at 35. From the Pp and the corresponding fatigue cycle counts, the fatigue diagram of Fig. 3 is constructed by the computer, as indicated at 36.
  • the chosen Pp is similarly derived from the BS.
  • the martensite index of the tested cable is computed, as indicated at 37.
  • Said martensite index is then compared to the said fatigue diagram, as indicated at 38, by entering it as the ordinate and determining the number of fatigue cycles that corresponds to it.
  • This does not mean that the cable's martensitic phase has necessarily been generated by fatigue cycles. It may have been generated by other causes, but by determining the number of fatigue cycles that corresponds to it, and therefore the residual number of fatigue cycles that the cable could still be submitted to before causing failure, the state of the cable can be evaluated, and, in the light of the conditions to which it has been submitted in its previous service, its residual expected life under the same conditions can be estimated.
  • the fact that the output of the computer 33 is indicated at 39 as "number of fatigue cycles" should be understood in the light of what has been said, viz. as meaning an index of the state of the cable and of its expected residual life, whether the cable has been and/or will be stressed by fatigue cycles or by any other cause.
  • the martensite index which is correlated to the change in the mechanical strength of the cable, is calculated by any one of the methods described below. Such a change may be due to successive fatigue stresses, and this is the case to which particular reference is made herein; however, it could be due to another cause, and the method of this invention will be applicable in the same way, though the diagram relating the martensite index to the cause of the change in mechanical properties will not be a fatigue diagram.
  • a different martensite index will correspond to different strengths of the cable.
  • the result, for an increasing number of fatigue cycles, is shown in Fig. 3, wherein the martensite index has been calculated by method 2, hereinafter defined.
  • each point of the graph is an average of three different measurements - a number of different measurements can be used in any embodiment of the invention - and the measurements were taken at predetermined intervals of the same number of fatigue cycles. If the fatigue cycles cannot be numbered, the measurements will be taken at predetermined time intervals.
  • the ordinates of a graph such that of Fig. 2 or Fig. 3 indicates a total amount of deformation induced by the amount of the magnetic phase present in the cable and hence permits to estimate its condition.
  • An index R which is what has been called “martensite index”, for the condition of a tested cable can be determined by one of the following procedures:
  • the two peaks are: the higher, central peak in Fig. 2, that is similar to that found in testing the master cable (the peak of Fig. 1), and the new peak - the left-hand, lower peak - of Fig. 2, which did not appear in the measurements of the master cable.
  • the border points, between which the integration for each peak is performed, are: for the lower (left-hand in Fig. 2) peak, from the beginning of the diagram (lowest magnetic field strength) to the minimum between the two peaks (point I in Fig. 2); for the higher (central in Fig. 2) peak, from the minimum between the two peaks (point I in Fig. 2) to the point in which the BS intensity has decreased to background noise value.
  • any one of said R indicators, or a combination of them, can be selected for use, according to the existing conditions, or as is convenient.
  • the BS readings are obtained periodically and each obtained in one of the resulting readings is analyzed by the following procedure. For example, if the first of the above procedures is used, the area of the left-hand part of the plot, which includes the peak, is measured. The ratio R for the measurement is determined and compared to a reference curve such as that of Fig. 3, previously prepared for the same cable, or for a master cable, indicating the R ratio for the master cable for different number of fatigue cycles.
  • the expected lifetime, before failure of the cable under consideration can be calculated if a constant fatigue rate is assumed, when the ratio for the same rate of fatigue cycles is compared between the master cable and the tested cable. More particularly, if a ratio Ri is calculated for the tested cable, and the master cable is known to have the same ratio Ri after, for example, 140 fatigue cycles, it can be assumed that the tested cable has been passed about 140 fatigue cycles during its period of use.
  • the calculation of the expected lifetime can be made by considering the ratio determined by one of the above procedures, or by averaging the ratios determined by two or more of the above procedures.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Abstract

L'invention concerne un procédé et un appareil de détermination des propriétés mécaniques de câbles ou fils en acier inoxydable, le procédé consistant à comparer la quantité de phase martensitique induite par contrainte et la phase austénitique d'origine dans le câble testé. On détermine la phase magnétique d'origine en recueillant des données de ligne de base du signal de Barkhausen (BS) d'un câble principal, ces données étant choisies, pour chaque câble en acier inoxydable à tester, entre le câble et un câble équivalent, et on détermine la quantité de phase martensitique en recueillant des données successives de BS pour le câble. On effectue une comparaison entre la quantité de phase martensitique induite par contrainte et la phase magnétique d'origine en déterminant un indice de martensite qui représente le rapport entre deux paramètres de phase et qui se réfère au câble testé et au câble principal respectivement.
EP99910640A 1998-04-27 1999-03-22 Procede et appareil non destructifs et en ligne de determination des proprietes mecaniques de cables en acier inoxydable Withdrawn EP1076821A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
IL12423798 1998-04-27
IL12423798 1998-04-27
PCT/IL1999/000152 WO1999056122A1 (fr) 1998-04-27 1999-03-22 Procede et appareil non destructifs et en ligne de determination des proprietes mecaniques de cables en acier inoxydable

Publications (1)

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EP1076821A1 true EP1076821A1 (fr) 2001-02-21

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EP99910640A Withdrawn EP1076821A1 (fr) 1998-04-27 1999-03-22 Procede et appareil non destructifs et en ligne de determination des proprietes mecaniques de cables en acier inoxydable

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EP (1) EP1076821A1 (fr)
AU (1) AU2953999A (fr)
WO (1) WO1999056122A1 (fr)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5514328A (en) * 1995-05-12 1996-05-07 Stoody Deloro Stellite, Inc. Cavitation erosion resistent steel
US5619135A (en) * 1995-07-17 1997-04-08 American Iron And Steel Institute Steel characteristics measurement system using Barkhausen jump sum rate and magnetic field intensity and method of using same
JPH09329593A (ja) * 1996-06-11 1997-12-22 Mitsubishi Heavy Ind Ltd ２相ステンレス鋼の脆化検出法
IL119579A (en) * 1996-11-07 2000-06-01 Case Technologies Ltd Method and apparatus for the on-line measurement of the strength of metal cables

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9956122A1 *

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AU2953999A (en) 1999-11-16
WO1999056122A1 (fr) 1999-11-04

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