Yu. Ya. Reutov

Feasibilities of Using the ELCUT Software for Calculations in Nondestructive Testing

Examples of calculations of typical nondestructive testing problems with the use of the ELCUT 4.1 software designed for simulating the physical fields are given. A method which permits, using this software, to increase significantly the accuracy and the reproducibility of the results is proposed. The calculation results obtained using versions 4.1 and 4.2 of the ELCUT software are compared. It is shown that the calculations carried out with the use of versions 4.1 of the software distributed freely via the Internet makes it possible to establish the basic relations of the problems solved.

Possibilities for the selection of magnetic field transducers for nondestructive testing

Magnetic field transducers that vary in their suitability for use in contemporary magnetic nondestructive testing are considered. The experimental data on the resolution of some transducer types are presented.

On complex permeability in eddy-current flaw detection

This paper critically considers attempts to prove the frequency dependences of the electrical conductivity and magnetic permeability of metals at frequencies lower than 1 MHz. Such attempts were made by certain authors when studying the operation of eddy-current transducers. It is shown that the complex character of the output voltage of an eddy-current transducer is determined by the vector summation of the magnetic fluxes of the primary magnetizing alternating field and the field of eddy currents, which are induced by the primary field, in a tested article. The frequency dependence of the results of this summation is quite sufficient for a physically correct description of the operation of an eddy-current transducer without involving a hypothesis on the frequency dependence of the physical constants of the material of the tested article.

A sensitive fluxgate magnetometer

A sensitive magnetometer whose fluxgate transducer is assembled using finished winding components produced by the radioelectronics industry is described. The maximum scale value of the magnetometer is 100 μT; the self-noise does not exceed 10 nT. During 8 h of operation, the zero shift is no more than 10 nT. At an 18-V supply voltage, the input dc is no more than 45 mA.

Magnetic Field of a Circular Butt Weld of a Trunk Oil and Gas Pipeline

The results of computer simulation (using the ELCUT software) of the magnetic field of a weld of ferromagnetic pipes both in the weld body and from outside the weld are given. Both linear and nonlinear cases of magnetization are considered. It is shown that in the nonlinear case the magnetic permeability and induction in the weld body are extremely nonuniformly distributed over its thickness, i.e., different weld layers operate on significant different sections of the magnetization curve.

The ways of reliable detection of metal inclusions by an eddy-current device

The ways of processing signals of an eddy-current probe in the reception channel of an induction metal detector are considered. It has been shown that the reliable detection of a metal article is possible only if both orthogonal signal components on the phase plane from the article are detected. The ways of complex indication of the orthogonal signal components and elimination of noise caused by unbalance of the eddy-current probe are described.

Some Aspect of Using a Magnetoresistive Transducer

The results of investigating the lower sensitivity threshold of a magnetoresistive transducer converting the magnetic field induction into an electric signal are presented. The voltage fluctuation amplitude measured in terms of the magnetic field induction units amounts to 25 × 10–9 T at the transducer output. It is found that after termination of the action of the magnetic field the output transducer voltage returns to the zero level with a delay. The duration of this return may amount to tens of minutes (depending on the induction and duration of the field action). A digital magnetometer with the scale of ±200 μT graduated to 0.1 μT is fabricated on the basis of the magnetoresistive transducer.

Choice of the Number of Shells for a Spherical Magnetostatic Shield

A criterion of advisability of using one or another number of shells in a shield for obtaining the maximum shielding effectiveness is found by using the well-known approximate formula for the shielding factor of a magnetostatic spherical shield with an arbitrary number of shells. As this criterion, it is proposed to use twice the product of the shield material permeability by the square of the total thickness expressed in terms of the shield radius. It is shown that a deviation from the optimum number of the shells leads to considerable losses in the shielding effectiveness.

Physical interpretation of magnetostatic shielding

Plausible physical mechanisms of the effect of a magnetic shield are considered. The shield is treated as a shunt for magnetic flux, as a compensator of an external field by means of fictitious magnetic charges, and as a solenoid compensating for an external field by means of molecular Ampere currents. None of the listed mechanisms taken separately can account for all aspects of magnetic shielding. This effect can be described adequately only if a complex approach is endorsed. Examples of calculations and measurements of magnetic parameters of shields, and their designs are presented.

Hysteretic effects in compensation for signals from gradient ferromagnetic transducers

Effects of residual magnetization in compensating components (rods) on the accuracy of compensation for undesired signals due to the terrestrial magnetic field in a primary gradient transducer of magnetic field are considered. The maximal relative error in compensation is determined by the ratio between the coercive force of the material of the compensating component and the maximal strength of the undesired magnetic field present in operational conditions. If a magnetically soft material (usually it is a Permalloy) is used in the compensating components, the error due to the hysteretic effects is within 5–10%.