Metal Magnetic Memory Technique Research Articles

Evaluation of residual load-bearing capacity for corroded steel strands via MMM technique

The quantitative evaluation of the residual load-carrying capacity of corroded cables is critical to the safe service of bridge structures. In this study, the locally corroded steel strands with different corrosion degrees were obtained through electrochemical experiments and the metal magnetic memory (MMM) signals were collected by the TSC-9 M-12 tester. The tensile failure tests of corroded steel strands were conducted by the WAW-1000 tensile testing machine. The distribution laws of the normal component Hz signals for steel strands in different corrosion cases were detailed and a three-dimensional (3D) magnetic dipole model of corroded steel strands was developed considering the end effects. The linear relationships between the magnetic characteristic quantity Hn and the corrosion cross-section loss rate As were revealed and verified by the theoretical and finite element simulation results. Based on the above relationships, a quantitative linear relationship between the residual load-carrying capacity F and the corrosion cross-section loss rate As of the corroded steel strand was proposed. The relative errors of the residual load-carrying capacity F calculated by the proposed quantitative method were overall within 20%. This study provides a basis for evaluating the residual load-carrying capacity of corroded cables using the MMM technique.

Quantitative method for evaluating corrosion defects and residual bearing capacity of bridge structural steel via MMM technique

The quantitative assessment of corrosion defects and residual bearing capacity is essential to ensure the safe operation of bridge steel structures. In this study, Q345qD steel was selected as the research object, and specimens with different corrosion levels were prepared using the electrochemical corrosion method. Metal magnetic memory (MMM) detection experiments and uniaxial tensile experiments on corroded steel plates were performed. A three-dimensional magnetic charge model of a corroded steel plate considering the end effect was built to explain the variation of the MMM signals. The finite element simulation results of the corroded steel plates were consistent with the experimental and theoretical results. Based on experimental and finite element data, the quantitative relationship between the corrosion depth h and the magnetic characteristic parameter Hn(z) is established with a relative error within 15 %. A quantitative relationship between the nominal tensile strength σu and the magnetic characteristic parameter Hn(z) is proposed with an evaluation accuracy within ±5 MPa. It is suggested that the proposed evaluation method is feasible in quantitatively evaluating the defects and residual tensile strength of corroded steel plates using the MMM technique.

Effect of Tensile Stress on Self-Magnetic Leakage Field in Carbon Steel Pipe Material

Metal magnetic memory (MMM) technique is a promising non-destructive technology for determining the state of material deformation and structural defect in carbon steel pipe by measuring the self-magnetic leakage field (SMLF). The relationship between SMLF and stress concentration of cracked specimens has been extensively researched, but little is known about corrosion defects in carbon steel pipes, such as circular holes. A static tensile test and MMM measurement were performed on the ASTM A106 Gr. B steel to investigate its applicability in predicting material deformation state and structural defect. The tensile load makes the distribution of self-magnetic leakage field, SMLF intensities in the elastic stage regular. In the defect zone of defective specimens, a peak-trough in the SMLF intensity in the tangential component, Hp(x), and a peak in the normal component, Hp(y), were observed. As yield approached, the SMLF intensities remained unchanged. During plastic deformation, dislocation slip and dislocation interaction rarely change the SMLF intensities and its gradient. The SMLF intensities and its gradient rise as the tensile load approach its ultimate strength. The distribution of SMLF intensities show a peak feature in the Hp(x), and a peak-trough in the Hp(y) as the specimen fractures. Variations in the magnetic and stress fields of carbon steel pipe are caused by structural defect. As a result, the SMLF intensity varies. The method described in this study can be applied to MMM technique to detect material deformation states and defect formation in ASTM A106 Gr. B steel at low cost and with minimal equipment.

Fast reconstruction method for defect profiles of ferromagnetic materials based on metal magnetic memory technique

In this paper, a fast reconstruction method for surface defect profiles of ferromagnetic materials is proposed based on the metal magnetic memory technology. An improved magnetic charge model that can adapt to rectangular and V-shaped defect profiles and a new particle swarm optimization algorithm based on a chaotic initial distribution, sigmoid inertia weight coefficient, and sine cosine acceleration coefficients are established as the forward model and iterative means of the method, respectively. The proposed method is verified with theoretical and experimental data, and the influence of noise is considered. The reconstruction method has good accuracy, repeatability, and robustness.

A numerical simulation method of residual magnetic field signals for evaluating deformation-induced stress concentration in ferromagnetic materials

The metal magnetic memory (MMM) technique is a promising non-destructive inspection method that is sensitive to early damage due to stress concentration in ferromagnetic components. However, quantitative analysis methods for evaluating the stress concentration induced by local plastic deformation have not yet been sufficiently studied due to the lack of a reasonable numerical simulation method. Based on the Jiles-Atherton (J-A) magneto-plastic model, which considers the combined effects of residual stress and strain, the change in the behaviour of residual magnetic field (RMF) signals in an X80 pipeline steel specimen with an indentation is calculated in this paper using finite element (FE) simulations, while systematic experimental research is also carried out. The results show that the model-predicted RMF signals are consistent with the experimental data, which demonstrates the validity of the numerical simulation method. Moreover, the comparison indicates that the RMF FE simulations can provide an effective and reliable way to determine the location and the degree of deformation-induced stress concentration. In addition, the effect of the residual stress and strain on the surface magnetic field and the model is discussed. The results of this study help to improve the accuracy of the MMM technique for evaluating the stress concentration caused by local plastic deformation.

Diagnostics of power boiler superheater tubes made of austenitic steel using the metal magnetic memory technique

Diagnostics of power boiler superheater tubes made of austenitic steel using the metal magnetic memory technique

Fatigue damage analysis of prefabricated concrete composite beams based on metal magnetic memory technique

Current studies have shown that using magnetic field change around the ferromagnetic material to characterize the fatigue damage is very effective, but researches on using metal magnetic memory (MMM) technique to detect fatigue damage are mostly limited to the material level. There are few studies on the mechanism of the magnetic signal change or numerical simulations at the member level. In this paper, cyclic loading tests were carried out on 8 prefabricated concrete composite beam specimens using wet connection technology. The relationship between the variation in the magnetic field of the steel reinforcement and the interface peeling damage of the specimens were investigated. Based on the magnetic flux density, the interface deformation, and the longitudinal bar strain, the mechanism of the magnetic signal change in different stages as well as interface peeling’s effect on the magnetic flux density were revealed. The feasibility of using the MMM field to characterize the fatigue damage of the composite spcimens was thus verified. Meanwhile, based on the modified J-A-S model, the model for magnetization change of prefabricated reinforced concrete components was established. By comparing the experimental and the simulation results, it is verified that the proposed model could effectively describe the magnetization change trend of the composite spcimens during the fatigue process.

An extended magnetic-stress coupling model of ferromagnetic materials based on energy conservation law and its application in metal magnetic memory technique

An extended magnetic-stress coupling model based on energy conservation law was established for ferromagnetic materials in low-intensity magnetic fields to develop the metal magnetic memory (MMM) technique, and its application was quantitatively analyzed using the finite element method. Firstly, the verification of the proposed model was given by comparing the influences of stress on relative permeability and residual magnetic field (RMF) signals with experimental data and other theoretical model. Then, the effect of the defect type, size, load magnitude, and lift-off value on the RMF signals was respectively discussed, and their sensitivities on the total characteristic parameter of RMF gradients were compared. In addition, the combined influence of the lift-off value and the defect depth was analyzed. The results indicate that the proposed magneto-stress coupling model is feasible to predict the stress state and structure damage using the MMM technique.

A method for quickly evaluating heat treatment quality of 35CrMo steel cylinder using magnetic properties

Seamless steel cylinders are widely used in real-life situations, and heat treatment has an important effect on their service life. The common methods used for heat treatment quality monitoring have many shortcomings, such as destructive operation, high cost and low coverage. To quickly and accurately evaluate the performance of the cylinder after heat treatment, a fast non-destructive testing method is introduced based on the coercive force measurement. The amount of residual stress for 35CrMo steel cylinder before and after heat treatment was evaluated quantitatively by the Metal Magnetic Memory technique, and the structural-mechanical dependence of coercive force was also revealed. Due to the grain refinement and the stress relief, the modified magnetic field index △H and k(x)of 35CrMo steel after heat treated are significantly decreased by 54% and 56%, respectively. Correspondingly, the magnetic coercive force is inversely proportional to the grain size, which is verified by hardness test. The structural-mechanical states of 35CrMo steel cylinder can be justified by measuring their coercive force, which is potential to be used as a reliable, accurate and non-destructive tool for mass production.

Investigation of the Impact of Load on the Magnetic Field Strength of the Crane by the Magnetic Metal Memory Technique.

The paper deals with the problem of applicability of the metal magnetic memory (MMM) technique in the crane structural inspection and monitoring. The MMM method does not require the external magnetization of a structure that results in reduction of downtime of maintenance operations. Measurement of the intensity of the self-magnetic leakage signal can be an alternative to other non-destructive methods used for inspection of a large crane’s structure and equipment. However, the complexity of the residual magnetization effect in the MMM technique is the problem with its application. Thus, the magnetic flux leakage behavior on the crane girder surface under different measurements and the crane’s load conditions is analyzed based on the results obtained during experiments carried out on the overhead traveling crane.

A dual-dipole model for stress concentration evaluation based on magnetic scalar potential analysis

Experiment shows that the normal component and the amplitude of the spontaneous magnetic signals on the surface of the ferromagnetic part, induced by a stress concentration zone (SCZ) caused by local plastic deformation, have only one peak. These waveform characteristics are precisely opposite of the defect identification criteria proposed by the metal magnetic memory (MMM) method, which include that the normal component of magnetic signals changes to its polarity and the tangential component reaches a peak value. At the beginning, a magnetic dual-dipole model is accordingly proposed to describe and evaluate the stress concentration in ferromagnetic materials. The contour maps of the magnetic scalar potential show that there is a magnetic source generated in the damaged area. This source can be simplified as a dual-dipole. It comes from the two peaks of stress variation at the edges of the SCZ. Furthermore, the maximum potential of magnetic anomalies was obtained. The values are influenced by the applied loading and deflection of the specimen. It decays exponentially with the increase of lift-off values in the air domain. Finally, residual stresses along the scanning line were measured to confirm the theoretical analysis. This dual-dipole model in the MMM technique is feasible to evaluate the stress concentration caused by local plastic deformation.

Comprehensive inspection of refrigerated ammonia storage tank welded joints by the metal magnetic memory technique and conventional NDT methods

Refrigerated ammonia storage tanks (RAST) are hazardous industrial facilities, where accidents with severe consequences occur. Defects of welded joints are one of the main reasons of RAST accident occurrence. Due to this, during the technical inspection, special attention is paid to quality control of welded joints. The use of non-destructive testing (NDT) for defect detection is essentially important as it can be used to assess the integrity of such critical steel structures as storage tanks. Among the several NDT techniques available, acoustic emission (AE) can supply valuable information assessing structural integrity, detecting flaws and leaks in base metal and welded joint. However, assessing structural integrity usually includes other NDT techniques (e.g., visual examination, ultrasonic testing, dye penetrant test) additionally to AE, providing complementarity between different NDT techniques. Nevertheless, conventional NDT methods are aimed at detecting only the defects that occurred during manufacturing and operation and do not assume stress-strained state (SSS) assessment. The metal magnetic memory (MMM) technique is a passive magnetic one that is recommended to be applied for SSS assessment in accordance with guidance documents. A flaw detectability relation between UT and MMM techniques is observed.

Study of the structure and mechanical properties of engineering products made of austenitic-martensitic steel, using the metal magnetic memory technique

Spontaneous phase transformation in local areas of the austenitic microstructure to martensite with the release of carbides may appear during the manufacturing or operation of engineering products made of two-phase austenitic-martensitic steel grades. When inspecting the quality of products made of these steels, the problem of detecting the local zones of the martensitic phase and carbide precipitation in the product metal arises. The article presents the results of an inspection by means of the metal magnetic memory (MMM) technique of centrifugal compressor impellers made of austenitic-martensitic steel 07Cr16Ni6. It was demonstrated that in the areas of stray field indications detected by means of the MMM technique, strength properties deteriorate, the metal structure degrades with abrupt changing of the metal phase composition and a carbide network formation, unacceptable δ-ferrite, was detected in the structure, and micro- and macro-cracks were found.

Magnetic Evaluation on Disassembly Damage of an Interference Fit Joint

Developing a method for disassembly damage evaluation is of great significance for the key components in maintenance and remanufacturing. Disassembly of the interference fit joint between the shaft and impeller, which could inevitably bring damages to the parts’ surface, was investigated. The ferromagnetic materials FV520B (impeller) and 40CrNiMo7 (shaft) were used in the disassembly experiments. Experiments showed that different damage degrees appeared on the disassembled interface as a result of single sliding friction under different loads. The stress concentration and plastic deformation stimulated changes in magnetic domains, which led to the distortion of surface spontaneous magnetic field and the induction of metal magnetic memory (MMM) signals. The tangential components of MMM signals had peak-trough features with zero-crossing points, and the normal components showed peak features. The visible features of the distorted MMM signals could locate the position of the defects. The average damage depth Sa, peak-trough difference Wpp and peak area S had been proposed as characteristic values. The linear relationship between Sa and Wpp, Sa and S was further obtained, respectively. It indicated that the MMM technique was capable of quantitatively evaluating the disassembly damage of ferromagnetic parts, which also provided a reference for the remanufacturability assessment and the selection of repairing processes in remanufacturing engineering.

금속자기기억법을 이용한 보일러 튜브 검사절차 유효성의 실험적 검증

금속자기기억법을 이용한 보일러 튜브 검사절차 유효성의 실험적 검증

Metallic Slit-Plate Dampers: Damage Evaluation with Metal Magnetic Memory Technique and Application to Structures with Rocking Columns

Inelastic deformation of metallic materials is one of the most effective mechanisms for the dissipation of energy input to a structure by an earthquake. Metallic dampers are special devices that resort to this source of energy dissipation, proving to be a cost-efficient solution for the seismic protection of structures. Two important issues arise when implementing metallic dampers in real structures: (1) Inelastic deformations cause damage that must be quantified after an earthquake to decide upon their eventual replacement; (2) dampers must possess an energy dissipation capacity large enough to endure severe earthquakes. This paper focuses on a particular type of metallic damper consisting of slit-plates made of stainless steel, applied to reinforced concrete frames with rocking columns at the first story. In particular, a new damage index based on the metallic magnetic memory (MMM) method is proposed and validated experimentally to quantify the damage of slit plate dampers subjected to cyclic loadings. Further, the seismic response of a frame with rocking columns that incorporate the damper is obtained to demonstrate that it can endure severe earthquakes without failing, and to emphasize the relevance of the proposed MMM damage index that would make its replacement after a severe earthquake unnecessary.

A method for identifying geometrical defects and stress concentration zones in MMM technique

Metal magnetic memory (MMM) technique is a kind of passive magnetic non-destructive inspection technique sensitive to early damage due to stress concentration in ferromagnetic components. However, geometrical defects and stress concentration zones probably coexist in an inspected component, which will make trouble for damage evaluation. In the paper, a 3-Dimensional (3D) numerical simulation based on a stress-induced magnetic anisotropic constitutive model is employed to produce the MMM signals of an ×80 pipeline steel plate with a center hole stretched in the geomagnetic field. The effects of the hole and the nearby stress-concentration zones on the MMM signal characteristics are respectively studied, and then a simple and convenient MMM signal processing method is proposed to identify two kinds of damage. This work is useful for improving accuracy of the MMM technique in damage evaluation.

Comparison between Magnetic Field Distribution Analysis and Metal Magnetic Memory (MMM) Testing Results Around Artificial Cracks under Loads

In this research, the behavior of the metal magnetic memory (MMM) signals near the artificial cracks located the back side of A572 specimens are tried. The materials are used as power transmission tower material. The variations of the MMM signals with the applied tensile loads are studied. It is found that both the tangential component, Hp(x), and the normal component, Hp(y), are effectively showed the stress concentration zone (SCZ) caused by discontinuities. The results of modeling and MMM technique showed that the loads create residual stress and lead to the change of magnetic field strength around artificial cracks in the specimen and that is relatively different from the crack free area. This research is useful for expending MMM method as a tool of nondestructive testing method for detecting subsurface flaws.

Magnetic Memory Inspection of an Overhead Crane Girder – Experimental Verification

Abstract The safety and efficiency of material handling systems involve periodical inspections and evaluation of transportation device technical conditions. That is particularly important in case of industrial cranes, since they are subjected to a large impact load and mechanical stresses acting on the crane's structure and equipment. The paper considers the possibility of a crane structure inspection using the metal magnetic memory (MMM) method. As an advanced non-destructive technique, this method can be employed for inspection of crane structure during operation, which leads to reduce the down time costs and increase the safety confidence in the monitoring process. The MMM technique is effective for early identification of the possible defect location and detecting the micro-damage in ferromagnetic structures through detecting the stress concentration areas. The basic principle of MMM method is the self-magnetic flux leakage signal that correlates with the degree of stress concentration. This method allows detecting early damage of ferromagnetic material through performing measurement in the earth magnetic field, without the use of a special magnetizing device. The paper presents the experimental results carried out on the double-girder overhead travelling crane with hoisting capacity 1000 kg. The influence of the load variation and duration time on the intensity of the self-magnetic flux leakage signal is analysed and discussed.

Strain Energy Based Method for Metal Magnetic Memory Effect of Tensile Tested Structures

The metal magnetic memory (MMM) technique has been widely regarded as an effective method to locate stress concentration zones and to identify structural defects. To study its applicability in prognostics of structure damage, a series of static tensile tests and MMM measurement were carried out on the commonly used Q235 steel. The experimental results show that the normal component of self-magnetic-flux-leakage signals \(H_p^z\) is linear with the position in loading direction x and the gradient \(G_{z,x}\) increases with an increase in the external load. 2D magnetostatic finite element analyses indicate that the variations of \(G_{z,x}\) should be due to the change in relative permeability of the specimen after the effect of mechanical loading under geomagnetic field. The strain energy density in the structure during loading is found to be exponentially determined by \(G_{z,x}\) with an adjusted R-squared value of 0.9984. The monotonous correlation enables prediction of structure damage using the MMM technique.