Abstract
The paper describes a dual-frequency method for reducing the impact of changes in the gap size between the eddy-current transducer and the pipe, as well as the pipe electrical conductivity on the eddy-current thickness gauge readings. A block-diagram of the dual-frequency eddycurrent thickness gauge is proposed for light-alloy drill pipes. The amplitude and signal phase dependencies on the wall thickness in the range from 6 to 17 mm and the gap in the range from 0 to 13.5 mm were studied, the results are presented. The digital signal processing algorithms based on the piecewise-linear approximation of low-frequency and high-frequency signal phase dependencies on the wall thickness are proposed. It is shown that the proposed correction algorithms can reduce the error caused by variations of electrical conductivity and the gap between the transducer and the pipe.
Highlights
Measuring the thickness of pipe wallsLight-alloy drill pipes of TB and TBP types made of aluminum alloy D16 are manufactured in accordance with the Russian standard GOST 23786-79 [1]
The pipe walls are worn during in-service use, and the wall thickness of the main pipe section must be controlled according to the Russian standard
To calibrate the readings when measuring a zero gap, the eddy-current transducer (ECT) is placed directly on the pipe and the high-frequency signal amplitude AHF0 is saved in the memory
Summary
Light-alloy drill pipes of TB and TBP types made of aluminum alloy D16 are manufactured in accordance with the Russian standard GOST 23786-79 [1]. The second frequency f2 is selected so that the signals of this frequency slightly depend on the pipe wall thickness and at the same time change with variations of the pipe electrical conductivity and the gap h between the pipe and the transducer. The dependence of the wall thickness T on the low-frequency signal phase φLF for a fixed value of the gap h (Figure 2) can be approximated by the piecewise-linear function [ ] ( ) ( ) T = KLF h, jtx ⋅ φLF + ΔφLF(tx) + ΔφLF + Kc ⋅ φLF + BLF h, jtx ,. Where KkHF( jhx) , BkHF( jhx) , KbHF( jhx) and BbHF( jhx) are the coefficients of piecewise-linear approximation of the dependence of the high-frequency signal phase on the gap
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