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 H ₀ increases. The increase in magnetizing field H ₀ 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, H _x (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.     

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.     

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 H ₀. 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 H ₀ and the effect of the aw width on the dependence of the aw field on H ₀: 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.     

Use of the Harmonic Analysis of an Induction Probe's Signal for Increasing the Information Content of Test Results

The harmonic content of a probe's electromotive force when magnetic testing is conducted with the use of alternating fields is significantly affected by the possible presence of a flaw in the specimen. Magnetic biasing of the specimen with a static field enables identification of internal flaws in addition to surface flaws. The electromotive force's harmonic content depends on the flaw's dimensions and depth. This circumstance can be used to determine these parameters in a separate way. The effect of a gap between the surface of a tested specimen and the probe is significantly weaker on the topography and amplitude of higher harmonics than on the corresponding parameters of the first harmonic. This observation, which holds for both internal and surface flaws, enables testing of larger gaps.     

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.