Issue << content << New Approach to Formulation of the Informative Parameters for Magnetic Structuroscopy (overview)


DOI: 10.12737/article_5d11fa6a064437.13543177

2019. Vol.22. No. 2, pp. 46–51

New Approach to Formulation of the Informative Parameters for Magnetic Structuroscopy (overview)

S. G. Sandomirsky

The main magnetic parameters sensitive to the structure of steels are the parameters of their saturation loop of magnetic hysteresis: the coercive force Нc and the remanent magnetization Mr. The saturation magnetization Ms is sensitive to the phase composition of steels. The variety of steel grades, heat treatment modes, and mechanical loads led to use of other magnetic characteristics for magnetic structuroscopy as well. Modern methods and devices are based on the measurements of the relaxation magnetic parameters of steels, their maximum, initial and maximum differential magnetic permeability’s. However, they can not guarantee a reliable inspection of the steel structure due to the limited measurement accuracy for these parameters. The author has established the relationships between the magnetic parameters of steels and their Нc, Mr and Ms. The article presents the developed formulas for calculating the maximum, initial and maximum differential magnetic permeabilities, all relaxation magnetic parameters of steels based on their Нc, Mr, Ms as well as examples of experimental substantiation of these relationships. Based on the analysis of the obtained regularities, we propose to formulate the informative parameters for the magnetic structuroscopy from the measured values of Нc, Mr and Ms of steels. Examples of such parameters are given. It is shown that their structural sensitivity is not decreased compared to the structural sensitivity of magnetic permeabilities and the relaxation magnetic parameters, and they can be measured in a simpler and more precise way. For magnetic structuroscopy of the steel 41Cr4 (DIN), for which Нc has not a unique relationship with the hardness in the whole range of variation of the tempering temperature Tt, we propose an algorithm Нc1 that allows to use the Нc and the ratio KS = Mr /Ms of the steel. We carry out the analysis of influence of the KS in its variation range for the steel 41Cr4 (DIN) on the maximum relative error of determining the parameter Нc1 from measurements of Нc and KS. It is shown that the results of the calculation according to the proposed algorithm uniquely depend on the Tt of the steel 41Cr4 (DIN) in the practically important range of its variation and are highly sensitive to changes in the hardness of the steel.
The result obtained makes it possible to abandon the complex and inaccurate measurements of the relaxation magnetic parameters and magnetic permeabilities of steels when elaborating methods and devices for magnetic structuroscopy, and to focus on improving the measurement accuracy of Нc, Mr and Ms of the material of products.
The practical task of bellows-type compensators trials with the use of probabilistic calculations reduces the understanding of the theory of probability to the objects of probable events and the relations between them, with their reduction to quantitative indicators. Simulation of trials using graphs clearly demonstrates the distribution of defective products in statistical experience, including hidden deviations from specified characteristics that are not detectable or difficult to detect using experienced statistics.
For the timely recognition of possible failures in the operation of the bellows equipment, regulatory documentation recommended only a continuous amount of acceptance tests. The use of a simplified inspection system by the method of independent random sampling from the party, with further extension of the results to all products is not allowed. Simplified inspection potentially reduces the reliability of the bellows compensator.
The simulation of testing processes allows, based on the calculated data, to optimize the sequence and order of testing with preservation of the required product quality and the requirements of regulatory and technical documentation.
Keywords: nondestructive testing, magnetic structural analysis, magnetic measurements, devices for magnetic structuroscopy, remanent magnetization; coercive force, saturation magnetization
 
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NDT in Mining Industry

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