NDTnet 1998 Aug, Vol.3 No.8

Abstract

There were results presented on mechanical properties of items made out of ferromagnetic materials using metal magnetic memory.
During the manufacturing of any ferromagnetic items there occurs simultaneous formation of crystal and magnetic structure of metal. In areas of most intensive concentration of defects (heterogeneous structure) with external field of the Earth (as a minimum) there occur points of domains fixation. In areas of maximum heterogeneities of the metal there occurs the total demagnetizing field of defects going out to the surface of the item as scattering magnetic fields.It was determined that when scanning along the item surface the areas of maximum heterogeneity of the metal structure are characterized by a line of polarity changing of normal component of the scattering magnetic field H^y_p (line H^y_p = 0), which can be easily determined by means of specialized devices - magnetometers. It was suggested to use this diagnostics parameters as quality criterion of machine engineering items also as criterion to detect their susceptibility to damage during operation.
The results on practical use of the proposed criterion were presented. In standard samples by their tensile testing - with high repeatability of the results - there was a neck formed and the samples were later damaged exactly along the line of polarity change of the normal component of the scattering field which was preliminarily measured on the sample surface prior to its placement in the tensile-testing unit.
There were examples considered to use metal magnetic memory method for quality control for heat treatment of the items and to study metal mechanical properties. For equipment in operation metal magnetic memory method is expedient to be used as a method to take representative samples of the metal also for early diagnostics of fatigue damage.

Based on the effect of magnetic metal memory in Russia there are developed techniques to test pipes, vessels and other equipment which were approved by Gosgortechnadzor of Russia. The techniques and specialized magnetometers based on computers were implemented at more than 200 plants in Russia, Ukraine, Poland, Bulgaria, India, China, Australia. In 1997 there was a testing program Round-Robin approved for metal magnetic memory to be included in the plan of International Welding Institute with participation of specialists from Germany and USA.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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