A. I. Pashagin

Problems of Evaluation of the Flaw Parameters in the Magnetic Nondestructive Testing

The magnetic leakage fields are investigated experimentally on rectangular-slit aw models for various magnetizing fields H0. It is shown that in certain cases the aw parameters can be incorrectly classified as a result of coincidence of their leakage fields. This is associated with both the choice of the magnetizing fields H0 and the effect of the aw width on the dependence of the aw field on H0: for wide aws this dependence is close to a linear function, whereas for narrow aws the dependence tends to the magnetization curve of the sample.

Magnetic-powder testing of components using magnetic indicator packages

Applications of magnetic indicator packages to magnetic-powder NDT are discussed. The sensitivity of this NDT technique can comply with GOST 21105-87 State Standard. The widthd of the deposited powder ridge as a function of magnetic field and flaw parameters is analyzed. The widthd can be used as either a criterion of the field magnitude or a characteristic flaw parameter.

Indication of magnetic fields with the use of galvanic currents in magnetic-powder nondestructive testing

A difference in the potentials in a nonuniform magnetic field is shown to occur across electrodes that are placed into a ferromagnetic suspension, which is used in magnetic-powder nondestructive testing (NDT). This phenomenon may be used for the detection of flaws in ferromagnetic products.

The possibility of measuring magnetic fields of flaws by using magnetic-powder suspensions

It is known that magnetic-powder testing is an indicator technique; a flaw in an article is inferred by the deposition of a magnetic suspension within flaw regions (segments) when articles are magnetized. Thus, the magnetic suspension does not allow quantitative evaluation of the field and, therefore, the parameters of the detected flaw. We have conducted some experiments allowing direct measurement of the magnetic field of a flaw by magnetic-powder suspensions. The resistivity was used as a characteristic proportional to the value of the field measured.

Dependence of the magnetic field of a flaw on the distance to the surface of a tested article

The dependence of the magnetic field of a flaw on the distance to the surface of a tested article has been studied for rectangular slot-type flaws. For flaws with a small opening width, it can be considered that their magnetic field decreases in inverse proportion to this distance, but with an increase in the flaw width, the field decreases more slowly.

A magnetic-field transducer based on a magnetic-field-controlled electrochemical cell

An electrochemical cell in which the electrolyte is a ferromagnetic suspension of a specific composition containing acidic electrolytic components was proposed for use as a transducer for the indication of magnetic fields. The voltage that forms at cell electrodes is due to changes of the suspension properties, which are induced by a magnetic field applied to the suspension. The dependence of the voltage on the electrolytic component percentage was studied and its increase was shown to increase the field sensitivity of the indicator; however, the sensitivity becomes nonlinear. The transducer can be used for the indication of both uniform and nonuniform magnetic fields produced by various sources. The absence of an individual power supply and simplicity are advantages of the transducer over previously used ones.

Nonuniform magnetization of an article around a flaw during magnetic inspection

Measurements of the induction in a ferromagnetic article directly around a surface flaw in the form of a rectangular slot have shown that there is a substantial magnetization nonuniformity of the article owing to the discontinuity. The nonuniformity smooths out as magnetizing field H0 increases. The increase in magnetizing field H0 increases the nonuniformity of the field distribution over the article surface, thereby changing the topography of the flaw field. In particular, in low magnetizing fields, this change leads to the absence of negative extrema in the curve of the tangential component of the flaw field, Hx(x). The discrepancy between the calculated and experimental values of the fields of flaws characterized by different geometric parameters is indicative of a considerable effect of the flaw opening on calculated data. These data should be improved through proper corrections obtained experimentally.

Testing of Mounting Hardware by Method of High-Frequency Magnetic Flux

We suggest using higher harmonics of the induction transducer output as sources of valuable information in tests of mounting hardware (nuts and bolts) by the method of high-frequency magnetic flux. In this case, spurious signals due to interfering features, such as edges of nut faces, are notably lower than in measurements of first harmonics. An instrument has been designed for testing two types of mounting hardware (nuts and bolts), which enables the operator to estimate flaw parameters and compare to those prescribed by the standards.

Portable Magnetic Flaw Detector Equipped with a Magnetic Indicator Bag

The design of a magnetic flaw detector with a magnetic bag used as a flaw indicator is discussed. Technical parameters of the detector and those of detected flaws are given.