Multiple coil eddy current probe and method of flaw detection
First Claim
1. An improved eddy current probe system for simultaneously detecting different types of flaws at different depths within a metallic wall, comprising:
- a. current means for generating alternating current of substantially different frequencies including a frequency adjuster and timing means;
b. a probe head including first and second coils in separate communication with said alternating currents of substantially different frequencies for detecting different types of flaws at different depths within said metallic wall, wherein the windings of one coil surround the windings of the other coil;
c. shielding means for preventing cross talk between said coils;
d. detector means for providing an electrical output representative of the relative impedance of the respective coils, ande. a computing means connected to said detector means and said current generating means for receiving and storing the value of the impedance of each coil as the probe head is moved across a portion of said metallic wall, and for transmitting control signals to said frequency adjuster and timing means which cause the current generating means to adjust the frequency of the alternating currents received by the coil so that impedance changes in the coils and hence the flaw-detecting resolution of each is maximized.
1 Assignment
0 Petitions
Accused Products
Abstract
An improved eddy current probe system and method for simultaneously detecting different types of flaws at different depths within a metallic wall, such as a section of Inconel tubing, is disclosed herein. The system comprises a current generator for generating alternating currents of substantially different frequencies, a probe head including first, second and third concentrically arranged coils in separate communication with the current generator, shielding material disposed between the coils for preventing cross talk between each coil and the pulsating magnetic field of the coils adjacent to it, and a detector circuit which may include an inductive bridge for providing an electrical output representative of the impedance changes in the respective coils. In operation, each of the coils conduct currents having substantially different frequencies, the highest frequency being conducted by the smallest-diametered coil and the lowest frequency being conducted by the largest-diametered coil. The different levels of magnetic field penetration provided by the coils as it is helically moved around the inside surface of a section on Inconel tubing not only allows the probe system to detect diverse kinds of flaws such as cracks, pits, or regions of thinning, but also flaws located at different depths throughout the tube wall. In the method of the invention, a computer is used to adjust the frequencies of the alternating currents conducted through the coils during the scanning operation in order to maximize the impedance changes in each coil, thereby maximizing the resolution of the probe system.
103 Citations
28 Claims
-
1. An improved eddy current probe system for simultaneously detecting different types of flaws at different depths within a metallic wall, comprising:
-
a. current means for generating alternating current of substantially different frequencies including a frequency adjuster and timing means; b. a probe head including first and second coils in separate communication with said alternating currents of substantially different frequencies for detecting different types of flaws at different depths within said metallic wall, wherein the windings of one coil surround the windings of the other coil; c. shielding means for preventing cross talk between said coils; d. detector means for providing an electrical output representative of the relative impedance of the respective coils, and e. a computing means connected to said detector means and said current generating means for receiving and storing the value of the impedance of each coil as the probe head is moved across a portion of said metallic wall, and for transmitting control signals to said frequency adjuster and timing means which cause the current generating means to adjust the frequency of the alternating currents received by the coil so that impedance changes in the coils and hence the flaw-detecting resolution of each is maximized. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. An improved eddy current probe system for simultaneously detecting different types of flaws at different depths within a metallic wall, comprising:
-
a. current means for generating alternating currents at a plurality of different frequencies, including a frequency adjuster and timing means; b. a probe head including a plurality of different coils having a different diameters arranged substantially concentrically, each of which is separately connected to said current means for receiving one of said currents of different frequencies; c. shielding means disposed between the edges of adjacent coils for preventing cross talk between the fluctuating magnetic fields generated by each coil and the coils adjacent to each such field; d. detector means for providing an electrical output representative of impedance changes in the respective coils, and e. a computing means connected to said detector means and said current generating means for receiving and storing the value of the impedance of each coil as the probe head is moved across a portion of said metallic wall, and for transmitting control signals to said frequency adjuster and timing means which cause the current generating means to adjust the frequency of the alternating currents received by the coils so that impedance changes in the coils and hence the flaw-detecting resolution of each is maximized - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
-
-
19. An improved eddy current probe system particularly adapted to be helically moved in sliding engagement against the inner wall of a metallic conduit for simultaneously detecting both large and small area flaws located at different depths within the conduit walls, comprising:
-
a. current generating means for generating alternating currents of different frequencies, and for changing the frequencies of any one of said currents in response to a frequency control signal; b. a probe head including a plurality of different coils having different diameters arranged concentrically, each of which is separately connected to said current generating means for receiving and conducting one of said alternating currents, wherein each of said coils includes a front face confrontable against said wall of said conduit for transmitting a pulsating magnetic field therefrom into said wall, and a rear face and wherein the smallest-diametered coil is provided with the highest frequency alternating current by the current generating means to provide a reference point for the system operator; c. shielding means for minimizing cross talk between said coils and said fields including ring-shaped walls of netic-conetic material disposed between the edges of adjacent coils; d. detector means for providing an electrical output representative of the relative impedance of the respective coils, and e. computing means connected to said detector means and said current generating means for receiving and storing the value of the impedance of each coil as the probe head is moved in sliding engagement against the inner wall of said metallic conduit, and for transmitting frequency control signals to a frequency adjuster and timing means connected to the current generating means which cause it to adjust the frequency of the alternating currents received by the coils so that the impedance changes detected by the coils and hence the flaw-detecting resolution of each is maximized. - View Dependent Claims (20, 21, 22, 23)
-
-
24. A method for simultaneously detecting different types of flaws in a metallic wall by an improved eddy current probe system that includes a current generating means for generating alternating currents of different frequencies, and a probe head having a plurality of different coils having different diameters arranged concentrically with respect to each other, each of which is separately connected to said current generating means, comprising the steps of:
-
a. conducting alternating currents of different frequencies through said coils while moving said probe head across a portion of said metallic wall, wherein the frequency of the current conducted through one coil is high enough to detect flaws on the surface of the wall confronting the probe head, and the frequency of the current conducted through another coil is low enough to detect flaws in said wall beyond said confronting wall surface; b. monitoring the impedance of the coils as the probe head is moved, and c. adjusting the frequencies of the alternating currents conducted through each of the coils to maximize the impedance change in each of the coils. - View Dependent Claims (25, 26, 27, 28)
-
Specification