Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1988-07-25
1990-08-07
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324700, G01R 2716
Patent
active
049471325
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for detecting thickness variations in the wall of a tubular body made of a material which is a conductor of electricity.
The problem of detecting corrosion of pipes arises not only in the case of buried pipes wherein the corrosion appears on the external face, but also in the case of pipes in which corrosive substances circulate, producing a corrosion on the internal face. In one or the other case, it is not possible to perform in a simple manner a visual inspection of the state of the pipes. That is the reason why different methods have been proposed, based on the measuring of magnetic or electrical parameters, which enable the obtaining of characteristic signals showing the state of corrosion of the pipe wall.
It has already been proposed in U.S. Pat. No. 4,048,558 to detect the existence of defects in the wall of a tube by using the "skin effect" whose depth is dependent upon the current frequency. This process consists in supplying a face of a tube with currents of different frequencies, and in measuring the impedance variation of this tube, in dependence upon the frequency. Each of these measurements is compared either to another section of the same tube, maintained at a temperature equal to that of the section of tube to be measured, or to a reference tube. This manner of proceeding makes it possible to dispense with parameters of resistivity and of permeability .rho. and .mu. which are dependent upon the metal of the tube and upon its temperature, so that the variations which will appear during the course of the comparison will necessarily be due to differences in the structure of the wall of the two compared tube sections. This manner of proceeding necessitates having, in the sample and in the reference pipe, the same values for .rho. and .mu.. This is not possible in the case of a buried pipe, it being given that one cannot reproduce on a reference pipe the same conditions as those in the buried pipe. Consequently, in that case, it is not only the possible defects which are unknown, but also the parameters .rho. and .mu..
The EP-0.175.257 has also proposed the detecting of defects on tubular conductors by using the skin effect. According to this method, the tubular conductor is supplied with alternating current of a determined frequency, in a given direction, generating a magnetic flux with a given direction, a voltage drop is picked up through two measuring points which are spaced apart from each other by a distance given with two measurement lines touching the tubular conductor, a first conducting loop is formed, from the measurement lines and the tubular conductor, with a useful induction surface which is as small as possible, a second conducting loop is formed, parallel to the direction of the current and perpendicular to that of the magnetic flux, with this second loop there is measured an induced voltage due to the change of magnetic flux, as near as possible to the measuring points, the voltage drop and the induced voltage are fed into an electronic evaluation circuit for measuring the voltage drop, and from the voltage drop and the induced voltage there is deduced the local resistance of the tubular conductor between the measuring points.
This method is not adapted for the measuring of defects on pipe segments several metres long, and for this reason, it necessitates having access to the tubular conductor over its entire length, since it necessitates a sort of auscultation of the external face of the conductor, and it only enables the measurement of very short segments, the auscultation device requiring to be moved along the tubular conductor.
In the case of buried pipes, the electrical measurements are rendered difficult and inaccurate, due to the influences of the earth which covers the pipe. That is the reason why it has also been proposed to mount the entirety of the apparatuses, for measuring and recording these measurements, on a mobile support which is intended to be introduced into the pipe and to be displaced there, drawn along either by t
REFERENCES:
patent: 2124577 (1938-07-01), Knerr
patent: 2593175 (1952-04-01), Packard et al.
patent: 3636441 (1972-01-01), Fujimura et al.
patent: 3786349 (1974-01-01), Devenyi
patent: 4048558 (1977-09-01), Goodman
patent: 4189778 (1980-02-01), Vogel
patent: 4683419 (1987-07-01), Neuelmann et al.
"The General Radio Experimenter", vol. 30, No. 11, Apr. 1956, A High Precision Impedance Comparator.
Industrial Laboratory, vol. 42, No. 2, pp. 292-295, 2/1976, Markochev et al., "Measurement Rate of Supercritical Crack Growth by Method of Potential Difference".
Charoy Alain
Gold Dieter
Kornmann Michel
Prost Jean-Louis
Vermot-Gaud Jacques
Battelle (Memorial Institute)
Eisenzopf Reinhard J.
Regan Maura K.
LandOfFree
Method for detecting thickness variations in the wall of a tubul does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for detecting thickness variations in the wall of a tubul, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for detecting thickness variations in the wall of a tubul will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-962746