RU98113860A - METHOD AND DEVICE FOR DETERMINING THICKNESS OF ELECTRICALLY CONDUCTING LAYER - Google Patents

Claims (11)

1. A method for determining the thickness (d _r ) of a protective layer (1) with an electrical conductivity k _{1 of a} part of a turbine installation, wherein a protective layer (1) is applied to the main material (2) of a part with an electrical conductivity of k ₂ , and wherein the electrical conductivity is k ₁ and k ₂ are different from each other, characterized in that
a) a high-frequency electric current is passed through an excitation coil (3),
b) the excitation coil (3) is brought closer to the protective layer (1) so that, at least in the protective layer (1), an electric eddy current is generated,
c) determine the value that is assigned to the impedance of the test coil (9), which, by the principle of eddy current control, serves as the basis for determining the thickness (d _r ) of the layer (1) and
d) the frequency (f) of the high-frequency electric current is chosen so that according to the principle of eddy-current control, an unambiguous determination of the thickness (d _r ) occurs with a ratio of electrical conductivities k ₂ / k ₁ between 0.7 and 1.5. 2. The method according to claim 1, characterized in that the frequency (f) of the high-frequency electric current is chosen so that the penetration depth (d) of the eddy current is greater than the maximum expected thickness (d _e ) of the protective layer (1), in particular up to about four times the maximum expected thickness (d _e ).  3. The method according to any one of the preceding paragraphs, characterized in that the frequency (f) of the electric current is selected between 1.5 MHz and 3.5 MHz, in particular between 2 MHz and 3 MHz.  4. The method according to any one of claims 1 to 3, characterized in that the value assigned to the impedance of the test coil (9) is determined by mechanical contact of the excitation coil (3) with the layer (1), and the test coil (3) is electrically isolated relative to the layer (1). 5. The method according to any one of claims 1 to 4, characterized in that the maximum expected thickness (d _e ) is determined approximately by means of a test measurement with a given test frequency (f _t ) and the frequency (f) is derived from this taking into account the conductivities k ₂ and k ₁ . 6. The method according to any one of claims 1 to 5, characterized in that
a) prepare a set of parts with a known layer thickness, serving as test bodies,
b) on each test body with a number of different approximate frequencies (f _p ), a value is assigned that is mapped to the impedance of the test coil (9), and
c) as the frequency (f), select the approximate frequency (f _p1 ) with a sufficiently high resolution and high linearity in magnitude, given in accordance with the impedance. 7. The method according to claim 6, characterized in that for the selection of approximate frequencies (f _p ), preliminary test bodies coated with a layer (1) are prepared, in particular, of simple geometry and with a plurality of test frequencies, the impedance of the test coil is matched (9) ) value, and from the test frequencies determine that with the best resolution and use as approximate frequencies. 8. The method according to any one of claims 1 to 7, characterized in that a certain value, adjusted to the impedance of the test coil (9), is compared with the reference values and the thickness (d _r ) of the protective layer (1) is determined from this.  9. The method according to any one of the preceding paragraphs, characterized in that it is implemented for a gas turbine blade with a protective layer (1) of an alloy of the MCrAlY type, where M is one of the metals iron, nickel and / or cobalt or an alloy of them, Cr is chromium Al is aluminum and Y is yttrium, hafnium, or a similar metal. 10. Device (4) for determining the thickness (d _r ) of the protective layer (1) with electric conductivity k _{1 of} the turbine plant component, and the protective layer (1) is deposited on the main material (2) of the component with electric conductivity k ₂ , and moreover, electric conductivity k ₁ and k ₂ are different from each other, characterized in that it contains an excitation coil (3), which is connected to an alternating current source (5), and a test coil (9), which is connected to the measuring unit (6) to determine impedance and with an evaluation unit for determining the thickness thickness (d _r ) layer (1).  11. The device (4) according to claim 10, characterized in that the excitation coil (3) is made flexible to create good mechanical contact with the layer (1).