EP0823053A1 - Procede et appareil de mesure d'objets ferromagnetiques - Google Patents

Procede et appareil de mesure d'objets ferromagnetiques

Info

Publication number
EP0823053A1
EP0823053A1 EP95922023A EP95922023A EP0823053A1 EP 0823053 A1 EP0823053 A1 EP 0823053A1 EP 95922023 A EP95922023 A EP 95922023A EP 95922023 A EP95922023 A EP 95922023A EP 0823053 A1 EP0823053 A1 EP 0823053A1
Authority
EP
European Patent Office
Prior art keywords
magnetic fields
coil
measuring means
anomalies
detecting
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Withdrawn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
EP95922023A
Other languages
German (de)
English (en)
Inventor
Göran Larsson
Jan Sundström
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Publication of EP0823053A1 publication Critical patent/EP0823053A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
    • G01N27/9013—Arrangements for scanning
    • G01N27/902—Arrangements for scanning by moving the sensors

Definitions

  • the present invention relates to a method and device for measuring ferro-magnetic objects with eddy current technology.
  • the flux thus generated in the core flows through a closed loop including pole pieces and a cylindrical section of the casing between the pole pieces. Between said pole pieces and in contact with the casing are a number of detectors placed around the circumference of the casing. Each detector has a set of coils. One of these detects flux perturbations caused by flaws, cracks or other anomaUes in the casing and the other detects eddy current which is an indication if the fault is on the inside or outside.
  • This method works weU for oil weU pipes and the like where the pipes are ferromagnetic and can be magnetically saturated. However, the pipe has to be empty in order to work, i.e. no cables or other objects can be present inside the pipe.
  • eddy current techniques have successfuUy been employed for detection of cracks and the like anomaUes on non- ferro-magnetic objects, for instance in the aviation and nuclear industry.
  • the eddy current techniques are used to find anomaUes that are maximum 1-2 mm below the surface. Another area of use for this method is to measure the thickness of coating layers.
  • Ultra-sonic techniques can penetrate deep into materials and are often used to check welds or measure of thickness. This technique requires that a contact media is placed on the ultra-sonic sender which limits the use to certain appUcations.
  • One object of the present invention is to provide a method and apparatus with a speciaUy designed transmitter/receiver which detects and indicates the defects and anomaUes of an object of ferro-magnetic material, especiaUy on surfaces with no direct access, such as the outside of pipes, the part of street lamp posts that are placed under ground, the outer side of reservoirs and tanks that are placed underground, without magnetic saturation and which does not require contact medias and can be used through layers of paint or other surface layers without affecting the test result.
  • a speciaUy designed transmitter/receiver which detects and indicates the defects and anomaUes of an object of ferro-magnetic material, especiaUy on surfaces with no direct access, such as the outside of pipes, the part of street lamp posts that are placed under ground, the outer side of reservoirs and tanks that are placed underground, without magnetic saturation and which does not require contact medias and can be used through layers of paint or other surface layers without affecting the test result.
  • a method for detecting anomaUes in objects of ferro-magnetic materials characterized in that a measuring means comprising at least one coil is placed against the object to be measured, that the coil is provided with alternate current, inducing eddy currents in the object, giving rise to magnetic fields which vary depending on the anomaUes, that the resulting magnetic fields are detected by the measuring means and that the detected magnetic fields are a measure of the degree of anomaUes in the object.
  • Fig. 1 shows a perspective side view of an embodiment of the measuring device according to the invention
  • Fig. 1A is a cross section taken along the line I-I in fig. 1,
  • Fig. 2A shows an enlarged cross- sectional front view of one arrangement of the transmitting and receiving coils in the probe
  • FFiigg.. 22BB shows an enlarged cross-sectional side view of one arrangement of the transmitting and receiving coils in the probe
  • Fig . 3A shows an enlarged cross-sectional front view of a second arrangement of the transmitting and receiving coils in the probe
  • Fig- 3B shows an enlarged cross- sectional side view of a second arrangement of the transmitting and receiving coils in the probe
  • Fig. 4 shows a cross- section of the probe along the line IV-IV in figs. 2B and 3B, and
  • Fig. 5 is a cross-sectional side view and shows an example of how the method according to the invention is used with an apparatus to detect anomaUes on a lamp post.
  • An embodiment of an apparatus 10 according to the invention, for measuring inside cylindrical objects such as lamp posts, shown in the figures comprises an elongated tube shaped part 11, referred to as arm, with a longitudinal axis A.
  • the arm 11 is beudable and remains in the desired bent shape. It is preferably made of a bendable metaUic hose 14 covered with a protective resiUent sheath 15, for example rubber or plastic, fig 1 A.
  • a probe 9 is attached in one end of the arm 11, a probe 9 is attached.
  • the probe 9 comprises a transmitting coil 20 and a receiving coU 22, figs. 2, 3 and 4, arranged under and adjacent to each other as seen along the axis A, with each coil being transverse to said axis A.
  • Two different sets of coils may be used.
  • One set is shown in fig. 2 and comprises two ferrite cores wherein the first is a transmitter 20 of the primary magnetic field into the object to be tested and the other core is the receiver 22 of the depoty magnetic field, a so caUed ''Driver Pick-up Probe".
  • the set shown in fig. 3 comprises a transmitter 20, 22 with a number of ferrite cores connected to each other with bridges and is fed with low frequency.
  • the coUs 20, 22 are protected and held in place by a housing or a cover 24.
  • the cover 24 may have the same cylindrical shape as the arm 11 but is preferably shaped so that an area 26 in front of the coils 20, 22 have a somewhat convex shape as seen along the arm 11. This area 26 is distinct in that the rest of the circumference of the probe 9 is separated with corner parts 28, fig. 4.
  • Tne other end of the arm 11 is preferably provided with a handle 12.
  • the coils 20, 22 are connected to electrical wires 13 which run inside the arm 11 and up through the handle 12.
  • the wires 13 are then connected to an eddy current detector and processor device 8 of known kind, such as for example Phasec 3.4 or 2.2 manufactured by Hocking NDT Ltd, but of course any device for detecting and displaying eddy current signals can be used.
  • the device is provided with a CRT display (Cathode Ray Tube) and memory faciUties in order to display and store measuring signals.
  • the eddy current device 8 feeds the transmitting coil 20 with alternate current via the electrical wires 13 inside the arm 11.
  • the probe 9 with the coUs 20, 22 is put against the object whose outside is to be measured.
  • the eddy currents induced by the transmitting coil 20 into the object penetrate the material and gives rise to magnetic fields which vary depending on the dimensions and anomaUes of the material. It has been found that the lower the frequency of the eddy currents the deeper it will penetrate, and far deeper without saturation of the object for ferro-magnetic materials than has been thought possible. Therefore, the transmitting cott 20 is speciaUy developed to use frequencies in the range of 1-100 kHz. Objects with a thickness of four millimetres have successfully been measured with this method.
  • the resulting magnetic field is detected by the receiving coil 22 and is a measure of the degree of anomaUes present in the object.
  • the receiving 22 coU is preferably of the same type as the transmitting coil 20.
  • the signal from the receiving coU is sent to and
  • the device is caUbrated against a reference object with the same material as for the object to be measured, and with predefined reference errors made on the reference object, before it is used for the first time in a specific appUcation.
  • the coils 20, 22 of the probe 9 are put against the reference object on the opposite side of the reference errors.
  • the errors could for example be grooves that are ground to specific depths, e.g. one, two and three millimetres.
  • the eddy current device feeds the transmitting probe 20 with alternate current which in turn induces eddy currents in the object which gives rise to magnetic fields.
  • the detected resulting magnetic field i.e. the output signal from the receiving probe, is then caUbrated so that it has a certain ampUtude on the display of the eddy current apparatus.
  • the object to be measured has a thickness of four millimetres and the eddy current apparatus is caUbrated so that the ampUtude from the reference error of one miUimetre corresponds to the distance between two lines in the grid of the display of the apparatus, two millimetres corresponds to two lines etc., it is then very easy to obtain a percentage of the errors by just looking at the ampUtude in that with these reference errors there is a twenty-five percent difference between the lines on the display. Of course, other reference errors may be chosen.
  • the apparatus is also caUbrated such that the material of the object to be measured provides peaks that are vertical on the display. If another material is encountered or a change has occurred in the material, the peak on the display has a different phase angle due to the difference in electrical conductivity for different materials. This is especiaUy useful in detecting, for example, if the galvanisation on a galvanised measured object has worn off in some areas on the object. This is immediately displayed by a different phase angle of the peak on the display.
  • the foUowing is an example of how the measuring technique is used for checking and evaluating lamp posts 31, fig. 5. These are often made of ferro-magnetic steel and are galvanised to withstand corrosion. They are usuaUy placed in a foundation 32 of concrete placed in the ground. A rubber ring 33 around the lamp post 31 in the area between the post and the foundation is thought to act as a seal. This is often not enough to prevent water from entering the space between the post 31 and the foundation 32 and is the area where corrosion is usuaUy formed.
  • the eddy current device 38 which is connected to the probe 39 via electrical wires 43, and the probe 39 are caUbrated against a reference object with the same material and thickness as the posts to be measured and with reference errors in order to obtain the ampUtude and desired phase angle of the peak.
  • the a ⁇ n 41 with the probe 39 is inserted into the inspection opening 34 of the lamp post 31.
  • the probe 39 is first held against the inside at an area where the outside is free of errors in order to reset the system-
  • the probe 39 has come out of contact with the surface due to the distinct area on the probe 39 in which the coUs are placed.
  • the probe 39 is then moved down and upwards along the inside of the post with the area with the coils in contact with the inside surface.
  • the operator "scans" the lower area 37 and the measuring values are stored in the eddy current device 38 and the position of the probe 39 at each value is recorded.
  • indicating means 16 fig. 1 which indicates how deep the probe is inserted into the post.
  • the eddy current coils will detect this and a peak wiU be displayed on the apparatus, the ampUtude of the peak depending on how affected the area is, i.e., how deep the corrosion has entered into the material.
  • the present invention is not limited to the embodiment described and can be changed within the scope of the patent claims to be foUowed.
  • the probe may have any desired shape depending on the appUcation as long as the transmitting and the receiving coUs are placed beside each other and with one of their ends facing the surface to be measured.
  • the mounting of the probe can naturaUy be done in any suitable fashion depending on the appUcation, and may, for example, be directly handheld.
  • the measuring device can be designed in a variety of ways within _the scope of the present invention. Because any eddy current apparatus can be used, it is also to be understood that multi-channel devices can be used in which unwanted signals can be filtered. Signal thresholds may also be used with these apparatus.

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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

Procédé et appareil permettant de détecter des anomalies dans des objets constitués de matériaux ferromagnétiques. Ledit appareil comporte un dispositif de mesure (9) doté d'au moins un bobinage (20), ledit bobinage étant placé contre un objet (1) à mesurer. Ce bobinage (20) reçoit du courant alternatif et induit dans l'objet (1) des courants de Foucault qui produisent des champs magnétiques variant selon les anomalies. Les champs magnétiques obtenus sont détectés par ledit dispositif de mesure et constituent une mesure du degré d'anomalies présentes dans l'objet (1).
EP95922023A 1995-04-24 1995-04-24 Procede et appareil de mesure d'objets ferromagnetiques Withdrawn EP0823053A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/SE1995/000444 WO1996034279A1 (fr) 1995-04-24 1995-04-24 Procede et appareil de mesure d'objets ferromagnetiques

Publications (1)

Publication Number Publication Date
EP0823053A1 true EP0823053A1 (fr) 1998-02-11

Family

ID=20397123

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95922023A Withdrawn EP0823053A1 (fr) 1995-04-24 1995-04-24 Procede et appareil de mesure d'objets ferromagnetiques

Country Status (4)

Country Link
EP (1) EP0823053A1 (fr)
AU (1) AU2685595A (fr)
FI (1) FI973993A (fr)
WO (1) WO1996034279A1 (fr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19829999C1 (de) * 1998-06-24 2000-01-13 Mannesmann Ag Verfahren und Meßgerät zur Detektierung der ordnungsgemäßen Einstecktiefe in einer Rohrpreßverbindung
AUPP813499A0 (en) * 1999-01-13 1999-02-04 Rock Solid Research Pty. Ltd. A subsurface pipeline inspection probe
GB0028787D0 (en) * 2000-11-27 2001-01-10 Dinsley Devices Ltd Apparatus for the detection and estimation of corrosion damage in the root section of metal lighting columns and similar columns
GB2404029B (en) * 2002-04-24 2005-11-09 Networksuk Ltd Defect detection device
GB0209333D0 (en) * 2002-04-24 2002-06-05 Electrical Testing Ltd Defect detection device
JP6213859B2 (ja) * 2013-03-29 2017-10-18 日本ファブテック株式会社 地際腐食損傷部の平均腐食深さの推定による残存平均板厚推定方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0652258B2 (ja) * 1987-11-09 1994-07-06 日本核燃料開発株式会社 過電流欠陥探傷方法及びその装置
US4855677A (en) * 1988-03-11 1989-08-08 Westinghouse Electric Corp. Multiple coil eddy current probe and method of flaw detection
GB8807301D0 (en) * 1988-03-26 1988-04-27 Philpot Electronics Ltd Detector
GB8826817D0 (en) * 1988-11-16 1988-12-21 Nat Nuclear Corp Ltd Eddy current non-destructive examination

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9634279A1 *

Also Published As

Publication number Publication date
WO1996034279A1 (fr) 1996-10-31
FI973993A (fi) 1997-12-17
AU2685595A (en) 1996-11-18
FI973993A0 (fi) 1997-10-17

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