Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1997-08-19
2000-04-18
Patidar, Jay
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
324230, 324234, G01N 2782
Patent
active
06051972&
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to inspecting metal tubes by eddy currents, and a major, although not exclusive, application thereof lies in inspecting the cladding tubes of rods containing a neutron-absorbing material or a fertile material for use in the control clusters of a nuclear reactor.
A method of inspecting the rods of control clusters by eddy currents that is already known (FR-A-2 585 869) corresponding to U.S. Pat. No. 4,741,878 to Gebelin et al makes use of coils through which the rods are caused to pass. The coils are powered by current at high frequency. Analyzing the voltage across the terminals of the coils and representing the impedance thereof makes it possible to evaluate tube wear.
That solution gives results which are satisfactory so long as the tubes are homogeneous, e.g. being made of stainless steel. However, it is no longer reliable if it uses conventional coils and the tubes have respective outer surface layers whose magnetic or electrical characteristics are significantly different from those of the bulk of the metal, e.g. because the tubes have been subjected to surface treatment for the purpose of reducing wear.
This applies in particular when the tubes are made of steel and have a surface layer that is 10 .mu.m thick to several tens of .mu.m thick, either of chromium which has electrical conductivity that is about six times greater than that of the base metal, or that is enriched in nitrogen obtained by electrical discharge in a rarified atmosphere containing nitrogen (ionic nitriding) and which is ferromagnetic.
SUMMARY OF THE INVENTION
The invention seeks in particular to provide a method and apparatus for inspection that satisfies practical requirements better than previously known methods and apparatus.
To this end, the invention provides, in particular, inspection apparatus comprising a measurement head having a measurement coil for surrounding the tube and means for powering the coil with voltage at high frequency, greater than 100 kHz, and for analyzing the impedance of the coil, the apparatus being characterized in that said head contains at least one magnet surrounding the coil and magnetic flux guides of material having high metallic permeability, on either side of the coil in the axial direction and co-operating with the magnet to constitute a magnetic circuit that creates a magnetic field whose maximum intensity lies inside the coil and close thereto.
In an advantageous embodiment, each of the guides is in the form of a ring having an external portion bearing against an end face of the magnet, and an internal portion converging towards the other guide and terminating in the immediate vicinity of the coil and substantially at the same level as the coil in the radial direction.
Generally, said means comprise an oscillator enabling the coil to be powered at a frequency that is variable in the range 100 kHz to at least 4 MHz.
In another aspect, the invention also provides a method of using eddy currents to inspect magnetic tubes having, on their outside faces, respective thin layers of magnetic or electrical characteristics that are different from those of the metal in depth, in which a coil surrounding the tube is powered by a voltage at high frequency lying in the range 100 kHz to 500 kHz in order to detect internal clearance, and at a higher frequency, and the part of the tube within the coil is simultaneously subjected to a continuous magnetic field that is of sufficient strength to saturate said thin layer magnetically, and the voltage across the terminals of the coil is analyzed.
In addition, the invention also seeks to make it possible to use eddy currents during a single measurement ass or two successive measurement passes, to detect variations along the tube in the clearance that exists between the tube and the material it contains.
For that purpose, the power supply means are designed to power the coil at the first frequency to detect internal clearance between the absorbent materials and the tube, and at a second frequency, grea
REFERENCES:
patent: 3441840 (1969-04-01), Randle
patent: 3760264 (1973-09-01), Zumbach
patent: 3761804 (1973-09-01), Steingroever
patent: 3803482 (1974-04-01), Steingroever
patent: 3922599 (1975-11-01), Steingroever
patent: 3986105 (1976-10-01), Nix et al.
patent: 5293117 (1994-03-01), Hwang
Bour Denis
Ducarme Stephane
Compagnie Generale des Matieres Nucleaires
Framatome
Patidar Jay
LandOfFree
Eddy current inspection of tubes with magnetic saturation by a c does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Eddy current inspection of tubes with magnetic saturation by a c, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Eddy current inspection of tubes with magnetic saturation by a c will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2338757