WO1993016380A1 - Method and apparatus for discontinuity detection in magnetisable material - Google Patents
Method and apparatus for discontinuity detection in magnetisable material Download PDFInfo
- Publication number
- WO1993016380A1 WO1993016380A1 PCT/GB1993/000264 GB9300264W WO9316380A1 WO 1993016380 A1 WO1993016380 A1 WO 1993016380A1 GB 9300264 W GB9300264 W GB 9300264W WO 9316380 A1 WO9316380 A1 WO 9316380A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- sensors
- pair
- warning means
- output signal
- differential
- Prior art date
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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
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
Definitions
- This invention relates to a method and apparatus for detecting magnetic discontinuities in magnetisable material.
- a method of detecting discontinuities in a magnetic material comprises: a) inducing a magnetic field within said material; b) providing an array of sensors at or near the surface of said material arranged to detect flux leakage from said material, said sensors in said array being electrically coupled in respective pairs; c) producing a differential output signal from a respective pair of said sensors, said differential signal being dependent on the difference between the output signals from the sensors comprising said respective pair; and d) actuating warning means in response to said differential output signal.
- both sensors Since the sensors comprising each pair are electrically coupled, where both sensors detect the same magnetic flux (i.e. where they are both positioned over homogenous material) the signals will cancel one another out and no differential signal will be produced by the pair.
- the change in magnetic flux detected by that sensor will cause a change in the output from that sensor such that a differential output signal will be produced by the pair of sensors of which that sensor is a member.
- any variation or difference in signals produced by sensors comprising a respective pair will produce a (differential) output signal from the pair, and thereby actuate the warning means.
- the warning means is arranged to be actuated however when the differential output signal from a respective pair of sensors reaches or exceeds a predetermined (threshold) value.
- this predetermined (threshold) value is variable.
- any differential output signal produced by respective pairs will only actuate the warning means when the output signal is greater than a predetermined threshold level. This enables the method to be "fine tuned" to detect discontinuities representing cracks or pits greater than a pre-determined physical size, and to ignore noise less than a pre-determined level.
- each respective pair is connected to warning means, preferably an audible or visible warning indicator arranged to detect an output signed from a respective pair of sensors.
- each respective pair is connected to a respective warning indicator.
- the array is typically mounted on a carriage which is moved over the surface of the material; once a warning indicator has been actuated, the carriage is stopped automatically and the two possible positions (i.e. corresponding to the respective positions of the members of the activated sensor pair) of the discontinuity may be physically marked on the surface of the material immediately above those two possible sites (typically by means of paint mark or the like), either manually or automatically. Subsequently, after the desired area of the surface of the material has been tested, the marked positions are re-tested by calibrated apparatus such as ultrasound non-destructive testing equipment, so as to give a quantitative value of the depth (and/or size) of the discontinuity (representing the crack or pit) below the surface of the material.
- calibrated apparatus such as ultrasound non-destructive testing equipment
- apparatus for detecting discontinuities in magnetisable material comprises: a) inducing means for inducing a magnetic field in said material; b) an array of sensors, each sensor arranged to detect and produce an output signal relating to, flux leakage at or near the surface of said material, said sensors being electrically coupled in respective pairs each pair of said sensors being arranged to produce a differential output signal dependent on the difference between said output signals produced by the individual sensors comprising each pair; and c) warning means arranged to be actuable in response to a differential output signal produced by a said pair of sensors.
- the inducing means, and the array of sensors, (and also preferably the warning means) are mounted on a movable carriage or trolley, which can .be moved relative to a ground surface on wheels or the like.
- the sensors are arranged in a linear array, with preferably one sensor of a first pair of sensors being provided intermediately between the sensors comprising a second pair of sensors. It is preferred that sensors comprising a pair of sensors are separated from one another by a plurality of intermediate sensors, said intermediate sensors comprising members of other pairs of sensors. It is preferred that the sensors used are solid state, preferably of the hall effect type; alternatively magnetodiodes or induction coil sensors may be used.
- calibration means is provided to inhibit actuation of the warning means where differential signals produced by respective pairs of sensors are below a predetermined threshold level.
- the calibration means is preferably adjustable such that the threshold level may be selectively varied.
- the warning means will be in the form of an audible or visible indicator.
- respective warning means are provided for each respective pair of sensors.
- the warning means comprise an array of warning lights, preferably arranged such that a pair of lights corresponds to a respective pair of sensors.
- the magnet will be a permanent magnet, advantageously of "horseshoe” type, although an electromagnet may be used as an alternative.
- the array of sensors is provided on a carrier member which carrier member is pivotally mounted on the carriage or trolley.
- the carrier or trolley is provided with independent drive means, such as a motor or the like arranged to power the apparatus.
- Figure 1 is a partly diagrammatic side view of apparatus for detecting magnetic discontinuities
- Figure 2 is a sectional plan view on the line A - A of the apparatus shown in Figure 1 ;
- Figure 3 is a plan view of the apparatus shown in Figures 1 and 2;
- Figure 4 is a schematic exemplary view of the sensor arrangement in the apparatus shown in Figures 1 to 3.
- the apparatus for detecting magnetic discontinuities in magnetisable material (such as corrosion pits or cracks in steel plate 16) is shown.
- the apparatus generally designated 1 , comprises a carriage or trolley 2 having wheels 4.
- a carrier 9 is pivotally mounted to the trolley 2 by means of pivot mountings 5.
- the trolley 2 comprises two compartments, a forward compartment housing balancing and trigger circuits and visual alarm in the form of an array of L.E.D ' s (best shown in Figure 3) 14.
- the rear compartment contains DC batteries 12, a drive motor and gearbox 3, and the trolley- drive wheels 4.
- the carrier 9 rides on a series of wheels 15 and seats a horseshoe magnet assembly comprising a magnet bridge 1 1 and neodymium-iron-boron rectangular magnets 13.
- a sensor head 6, also mounted on carrier 9, houses a linear array of thirty six Hall effect 7. It is attached to the magnet carriage by the pivot arms 8 and connected to the balance and trigger circuitry by cables 10.
- the magnets 13 are seated in the carrier 9 so as to be close to the surface of a steel plate 16 under examination, the gap between the pole pieces and the surface of the steel plate typically being adjustable.
- the sensor head comprises a rectangular box the lower half of which is made of a material known commercially as nylatron, chosen for its resistance to wear and abrasion.
- a printed circuit board (not shown) to which the sensor array is attached is fitted into the lower box and a lid of material commercially available under the trade mark Tufnol fitted to seal the sensors from dirt and moisture.
- the pivot arms 8 are adjusted to allow a small gap between the sensor head 6 and the steel plate 16 under examination. They allow the sensor head to ride upwards if the chamfered edges of it the sensor head 7 encounter protrusions or undulations in the steel plate surface.
- the sensors in the array are electrically connected in respective pairs (referred to as differential pairs) to balance and trigger circuitry 17 by connection cables 10.
- the pairs of differential sensors 7 are arranged in "overlapping" relationship with five sensors from adjacent differential pairs being located intermediate the sensors comprising a first differential pair.
- the sensors are therefore connected in the following pairs: 7a & 7g; 7b & 7/7 ; 7c & 7i; 7d & 7j; 7e & 7k; 7/& 71.
- the spacing between the- centres of adjacent sensors in the array is typically of the order of 7.5 mm, whereas the spacing between sensors comprising a differential pair is typically of the order Of 45mm.
- the magnetic field extension at the site of a discontinuity in a direction transverse to the direction of movement of the carriage may be 4 to 5 times greater that the dimension of the discontinuity in that direction, the spacing chosen for a differential pair of sensors should ensure that the signals from a typical defect do not tend to be self cancelling.
- the magnets 11 induce a magnetic field in the steel plate 16 under examination. Flux leakage from the plate 16 will vary depending on the presence or absence of magnetic discontinuities (such as pits or cracks) in the thickness of the plate.
- Each of the Hall effect sensors 7 in the array produces an electrical output signal proportional to the flux leakage at a corresponding point above the plate 16. Since the sensors 7 are arranged in differential pairs as described above, where both sensors comprising a pair lie above homogenous portions of the plate (i.e. where there are no cracks or pits) the respective output signals from each of the sensors comprising that pair will be substantially equal. In this case the differential signal produced by the balancing circuitry for that pair will be zero.
- each sensor comprising the pair will produce a different output signal in response to different values of flux leakage detected. This difference in individual sensor output signal results in a differential output signal for that respective pair of greater than zero being output from the balancing and triggering circuitry.
- Differential signals which exceed a predetermined calibration threshold (to reduce the effects of noise) trigger an output voltage to two of thirty six bi-colour light emitting diodes 14 corresponding to the differential pair of sensors detecting the discontinuity, changing the colour from green (balanced) to red (discontinuity).
- a ten turn digital potentiometer is provided to adjust the threshold value during calibration.
- the apparatus In use, the apparatus is moved at a steady speed across the surface of the specimen plate by the motor or manually. In the absence of any discontinuity there will be no output from the differential pairs of sensors to the trigger circuits, and all LED's will show in the green state. As a sensor passes over a discontinuity the balance with its pair is disturbed and an output signal fed to the trigger circuit; if this exceeds the threshold level, the corresponding LED's are changed to red. The operator stops the apparatus and marks the possible location of ⁇ * .discontinuity on the surface of the specimen plate.
- this apparatus has been shown to be capable of detecting corrosion pits penetrating to a depth of less than 30% of wall thickness in 6 to 10 mm plate.
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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 Or Analyzing Materials By The Use Of Magnetic Means (AREA)
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE0579807T DE579807T1 (en) | 1992-02-11 | 1993-02-05 | METHOD AND DEVICE FOR DETECTING DISCONTINUITIES IN MAGNETIZABLE MATERIAL. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9202846.3 | 1992-02-11 | ||
GB929202846A GB9202846D0 (en) | 1992-02-11 | 1992-02-11 | Method and apparatus for discontinuity detection in magnetisable material |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1993016380A1 true WO1993016380A1 (en) | 1993-08-19 |
Family
ID=10710175
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1993/000264 WO1993016380A1 (en) | 1992-02-11 | 1993-02-05 | Method and apparatus for discontinuity detection in magnetisable material |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0579807A1 (en) |
CA (1) | CA2107368A1 (en) |
DE (1) | DE579807T1 (en) |
GB (1) | GB9202846D0 (en) |
WO (1) | WO1993016380A1 (en) |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5614825A (en) * | 1994-11-28 | 1997-03-25 | Industrial Sensors And Actuators | Magnetic flux leakage inspection apparatus with surface-responsive sensor mounting |
WO1999002982A1 (en) * | 1997-07-09 | 1999-01-21 | Anatoly Alexandrovich Dubov | Method for determining the stress deformation condition of an article made of a ferro-magnetic material using magnetic field dispersion and device for realising the same |
WO2003056286A1 (en) * | 2001-12-25 | 2003-07-10 | Anatoly Aleksandrovich Dubov | Method for quality control of products (variants) |
DE102006006468A1 (en) * | 2006-02-10 | 2007-08-16 | Rwe Power Ag | Method for monitoring and / or non-destructive testing of a transmission element and measuring arrangement for carrying out the method |
WO2015197239A1 (en) * | 2014-06-27 | 2015-12-30 | Institut Dr. Foerster Gmbh & Co. Kg | Method and device for stray flow testing |
CN106353397A (en) * | 2016-09-06 | 2017-01-25 | 中国铁道科学研究院 | Vehicular magnetic flux leakage detecting equipment and system for steel rail surface damage |
RU2829469C1 (en) * | 2024-06-14 | 2024-10-30 | Федеральное государственное автономное образовательное учреждение высшего образования "Балтийский федеральный университет имени Иммануила Канта" (БФУ им. И. Канта) | Device for detecting micromagnetic particles in austenitic steels weld material |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2411211A1 (en) * | 1973-06-29 | 1975-03-20 | Amf Inc | PROCEDURE AND EQUIPMENT FOR IDENTIFICATION BY NON-DESTRUCTION-FREE TESTING OF DETECTED ANOMALIES ON A WORKPIECE |
US4218651A (en) * | 1975-07-25 | 1980-08-19 | Ivy Leon H | Apparatus for detecting longitudinal and transverse imperfections in elongated ferrous workpieces |
EP0073017A1 (en) * | 1981-08-19 | 1983-03-02 | Nukem GmbH | Device for the non-destructive testing of ferromagnetic objects |
EP0238209A2 (en) * | 1986-03-17 | 1987-09-23 | United Kingdom Atomic Energy Authority | Magnetic discontinuity detection |
-
1992
- 1992-02-11 GB GB929202846A patent/GB9202846D0/en active Pending
-
1993
- 1993-02-05 EP EP19930903253 patent/EP0579807A1/en not_active Withdrawn
- 1993-02-05 CA CA002107368A patent/CA2107368A1/en not_active Abandoned
- 1993-02-05 WO PCT/GB1993/000264 patent/WO1993016380A1/en not_active Application Discontinuation
- 1993-02-05 DE DE0579807T patent/DE579807T1/en active Pending
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE2411211A1 (en) * | 1973-06-29 | 1975-03-20 | Amf Inc | PROCEDURE AND EQUIPMENT FOR IDENTIFICATION BY NON-DESTRUCTION-FREE TESTING OF DETECTED ANOMALIES ON A WORKPIECE |
US4218651A (en) * | 1975-07-25 | 1980-08-19 | Ivy Leon H | Apparatus for detecting longitudinal and transverse imperfections in elongated ferrous workpieces |
EP0073017A1 (en) * | 1981-08-19 | 1983-03-02 | Nukem GmbH | Device for the non-destructive testing of ferromagnetic objects |
EP0238209A2 (en) * | 1986-03-17 | 1987-09-23 | United Kingdom Atomic Energy Authority | Magnetic discontinuity detection |
Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5614825A (en) * | 1994-11-28 | 1997-03-25 | Industrial Sensors And Actuators | Magnetic flux leakage inspection apparatus with surface-responsive sensor mounting |
WO1999002982A1 (en) * | 1997-07-09 | 1999-01-21 | Anatoly Alexandrovich Dubov | Method for determining the stress deformation condition of an article made of a ferro-magnetic material using magnetic field dispersion and device for realising the same |
DE19782287C2 (en) * | 1997-07-09 | 2003-11-27 | Anatoly Alexandrovich Dubov | Method for determining the stress and strain state of a product made of ferromagnetic material with magnetic control fields and device for carrying out this method |
WO2003056286A1 (en) * | 2001-12-25 | 2003-07-10 | Anatoly Aleksandrovich Dubov | Method for quality control of products (variants) |
DE102006006468A1 (en) * | 2006-02-10 | 2007-08-16 | Rwe Power Ag | Method for monitoring and / or non-destructive testing of a transmission element and measuring arrangement for carrying out the method |
WO2015197239A1 (en) * | 2014-06-27 | 2015-12-30 | Institut Dr. Foerster Gmbh & Co. Kg | Method and device for stray flow testing |
CN106574912A (en) * | 2014-06-27 | 2017-04-19 | 霍释特博士有限两合公司 | Method and device for stray flow testing |
RU2644026C1 (en) * | 2014-06-27 | 2018-02-07 | Институт Др. Фёрстер Гмбх Унд Ко. Кг | Method and device for testing using scattering flows |
US10082485B2 (en) | 2014-06-27 | 2018-09-25 | Institut Dr. Foerster Gmbh & Co. Kg | Method and apparatus for leakage flux testing |
CN106353397A (en) * | 2016-09-06 | 2017-01-25 | 中国铁道科学研究院 | Vehicular magnetic flux leakage detecting equipment and system for steel rail surface damage |
CN106353397B (en) * | 2016-09-06 | 2023-12-01 | 中国铁道科学研究院集团有限公司 | Device and system for detecting magnetic leakage of damage on top surface of vehicle-mounted steel rail |
RU2829469C1 (en) * | 2024-06-14 | 2024-10-30 | Федеральное государственное автономное образовательное учреждение высшего образования "Балтийский федеральный университет имени Иммануила Канта" (БФУ им. И. Канта) | Device for detecting micromagnetic particles in austenitic steels weld material |
Also Published As
Publication number | Publication date |
---|---|
DE579807T1 (en) | 1996-03-14 |
EP0579807A1 (en) | 1994-01-26 |
GB9202846D0 (en) | 1992-03-25 |
CA2107368A1 (en) | 1993-08-12 |
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