Portable instruments for multiparameter magnetic evaluation of material structures

The principles of operation and capabilities of portable computerized testing facilities of the MMT and SIMTEST series, which are intended for multiparameter magnetic evaluation of the structure of ferromagnetic articles of different dimensions, are described.     

Improving the Reliability of Eddy-Current Quality Control of Soldering in Current-Carrying Copper Joints and Expanding the Nomenclature of Inspected Joints in Energy Equipment

The possibilities of increasing the reliability of eddy-current quality control of soldering in current-carrying copper joints of the stator windings of electrical machines and expanding the nomenclature of inspected joints by using an improved eddy current transducer with a U-shaped core are investigated. To achieve this goal, rectangular cutouts were made in the poles of the U-shaped core, made of transformer steel plates, to allow the transducer to be mounted on a tested solder joint in two mutually perpendicular directions. Using such a transducer for testing allows one to induce closedloop eddy currents in the solder joint along these two directions, thus significantly improving the reliability of testing by virtue of all soldered surfaces in the joint contributing to the eddy-current transducer signal. The use of such a transducer also significantly expands the range of tested joints due to the possibility of exciting closed-loop eddy currents perpendicular to the direction of such joints (testing the side walls of the joints). It is shown that despite local changes in the distribution of electromagnetic field in the interpole space as compared to the case of no cuts, the presence of rectangular cuts in the poles of the U-shaped core of the eddy current transducer practically does not affect the accuracy of determining the degree of soldering of tested joints along and perpendicular to their direction.

     

Relation between the Residual Magnetization and Change in Magnetization on Steel and Alloy Return Curves

The relation between the residual magnetization M _r and change in magnetization on the return curves as a function of the coercive force is studied experimentally for heat-treated steels of different chemical compositions and a number of polycrystalline iron–nickel–cobalt alloys. It is shown that in the quenched condition the ratios M _s /M _r and M _r / are almost constant and close to 2 and 4, respectively, for all investigated steels regardless of their chemical composition. For highly tempered steels and annealed alloys these ratios represent structurally sensitive quantities depending on the critical fields in the material and characterize the relation between reversible and irreversible remagnetization processes. A model interpretation of the results obtained is given.     

Experimental Determination of Critical Fields of 90-Degree Domain Wall Displacement in Plastically Deformed Low-Carbon Steels

Experimental data are presented for the field dependences of differential magnetic permeability μ_d (H₀) of plastically deformed low-carbon steel-St3 samples both in an unloaded state and under tensile stresses. It is shown that applying tensile stresses drastically changes the shape of curves μ_d (H₀ ) a fact that indicates compensation of internal residual compressive stresses in the samples by external tensile stresses. A new technique is proposed for the experimental determination of the critical fields of displacement of 90-degree domain boundaries based on dependences μ_d (H₀ ). Residual compressive stresses in plastically deformed St3 steel are estimated.     

A procedure and device for calibration-free determination of residual compression stresses in low-carbon steels deformed by tension

A procedure for determining the residual compression stresses in tension-deformed low-carbon steels has been proposed that does not involve pre-calibration of the device with standard samples for the case where magnetic anisotropy is mainly determined by mechanical compression stresses. A new design of the attachable measuring transducer is presented for experimental determination of the induced magnetic-anisotropy field within local areas of lump ferromagnetic objects. The legitimacy of evaluating compression stresses with this procedure has been proved experimentally.     

Eddy Current Quality Control of Soldering in Superconducting Current-Carrying Joints with Allowance for the Effect of Cross Section Variations on Testing Results

Russian Journal of Nondestructive Testing - We propose a dual-frequency eddy current procedure for quality control of soldering in superconducting current-carrying joints of electromagnets. The...     

Multipurpose Use of Magnetic Properties of Steels in Nondestructive Testing of the Quality of Heat-Treated Workpieces

The paper is devoted to calculation of expressions relating the hardness both of a series of low-alloyed steels and of high-chromium steels 14Kh17N2A, 20Kh13, 30Kh13, and 40Kh13 with their magnetic properties after quenching and subsequent tempering over a wide temperature range. Expressions relating the hardness of 60S2A, 50G, and U8 steels with reading of a MS-2 magnetic structuroscope are also calculated. A table containing tempering temperature intervals on which the coercive force, the relaxation magnetization, and the magnetic susceptibility vary monotonically is given for a series of steel grades. Limits of variation of the above-mentioned quantities and the hardness are also given.     

Nondestructive Method for Testing Stress-Strain Properties of Oil Pipes

The results of study and statistical processing of the magnetic properties, namely, the coercive force and the relaxation magnetization, as well as the strength, plastic, and tensile properties of the 32G2S, 36G2S, and 38KhNM steels, used in fabricating oil pipes, as functions of the heating temperatures in quenching and tempering are given. Relations between the stress-strain and magnetic properties are estimated using the multiple correlation method. The introduction of the multiparameter nondestructive method for testing finished oil pipes at the Sinarsk Pipe Factory is described with reference to a plane-carbon steel of the D strength group and the 38KhNM low-alloyed steel of the E strength group.