Measurements of magnetic minor hysteresis loops have been performed in martensitic stainless steel subjected to tensile creep test at 120 MPa and 873 K. The minor-loop coefficients as well as coercivity, which are indicators of internal stress, sharply increase at the primary creep and show a very s low increase at the secondary creep, followed by the steady increase at the ternary creep. A good correlation of the coefficients with creep strain cl early shows that magnetic method using minor hysteresis lo...
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Changes of Magnetic Hysteresis Properties due to Creep Damage in Martensitic Stainless Steel

Abstract This paper investigated a feasibility of magnetic flux leakage (MFL) method using ac excitation for a nondestructive evaluation of wall thinning in nuclear power plants. Usually , MFL method uses dc field for exciting specimens, and only intensity of magnetic flux density is evaluated. Contrary, when alternating current is used for magnetizing specimens, not on ly amplitude of magnetic flux density but also phase difference is available. Therefore an evaluation with higher accuracy is expected. He...
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Evaluation of wall thinning by MFL method using ac excitation

Magnetic properties derived from major hysteresis loops are sensitive to the microstructures of iron-based steels and have therefore been used for nondestructive evaluation of degradation in ferromagnetic materials contained in structural components. A permeability obtained from ac small field excitation may be a more us eful parameter than one obtained from a major hysteresis loop from the viewpoints of electricity consumption and real-time measurement. In this paper, the relati on between the ac permeabi...
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Evaluation for Mechanical Properties of Ferromagnetic Steels by AC Permeability

This study demonstrates the possibility of applying magnetic methods to pressure vessel surveillanc e at nuclear power plants. Magnetic hesteresis-minor-loop measurement and TEM observation were pref ormed on thermally aged Fe-1.0wt%Cu model alloys. Minor loop parameters decreased with increasing a ging time. The mechanism is discussed in terms of Cu precipitation behaviors of cold-rolled alloys....
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Relation between Precipitation Behaviors and Magnetic Properties in Cold-rolled FeCu Model Alloys

This study demonstrates the possibility of applying magnetic methods to pressure vessel surveillance at nuclea r power plants. Charpy impact test and magnetic hysteresis-loop measurement were preformed on Fe-1.0wt%Cu model alloys. The ductile-brittle transition temperature and the coercivity increased by cold-rolling and thermal agi ng. This correlation originates from an increase in the dislocation density and a formation of Cu precipitates....
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Magnetic Properties of FeCu Model Alloys Embrittled by Cold-rolling and Thermal Aging

This study developed an apparatus for the measurement of magnetic properties of tensile test specimen. Experimental results show that the difference shape of BH curves of the steels cold-rolled with different rolling reduction. The coercive force has good correlation with Ductile-brittle transition temperature and Vickers hardness of the specimen. This result indicate s the possibility of nondestructive evaluation for the mechanical properties of tensile test pieces using magnetic methods....
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NDE for Mechanical Properties of Ferromagnetic Steels using Magnetic Measurement Apparatus

Basic study on applying magnetic flux leakage (MFL) method using ac excitation to a nondestructive evaluation of wall thinning occurred under reinforcing plates in nuclear power plants were performed. Frequently, MFL method by means of dc field for exciting specimens is adopted, and only intensity of magnetic flux density is evaluated. On the other hand, MFL with alternating current enable us to utilize not only amplitude of magnetic flux density but also phase difference, which contributes to evaluati...
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Nondestructive evaluation of wall thinning occurred under reinforced plate by MFL method

This paper describes an applicability of magnetic flux leakage (MFL) method for a nondestructive evaluation of wall thinning in nuclear power plants. Since MFL method has already be en applied to other industry field, this method should be an effective tool in nuclear power plants. Here, in order to investigate a possibility of MFL method for condition monitori ng of wall thinning, steels with slit were prepared and distribution of leakage magnetic flux was evaluated systematically using magnetic probe and...
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A possibility of MFL method for condition monitoring of wall thinning

Inconel 600 alloy, Ni base alloy, and SUS304 steel, austenitic stainless steel, are used for steam generators tubing, pressure vessel, etc. due to its high strength and high corrosion resistance. Stress corrosion cracking is attributed to sensitization at grain boundary occurs and it causes failures in plants. Though these alloys are paramagnet, they transforms into ferromagnetic along grain boundaries when sensitization occurs. Therefore nondestructive evaluation using magnetic measurement for sensiti...
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NDE for sensitization of Inconel 600 and SUS304 using magnetic field sensor

The possibility of simultaneously nondestructive evaluation for material deterioration and detecting sub-mm sized small defect were investigated using magnetic methods. The magnetic hysteresis properties and the distributions of leakage magnetic field were measured by a magnetic yoke and a magnetic field sensor. The hysteresis loop measurement was sensitive to deterioration in material and scanning flux distribution was effective for detection of sub-mm sized defect. The deterioration and small defect ...
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Simultaneously nondestructive evaluation of degradation and defect in sub-mm size using magnetic sensing techniques