Self-magnetic Leakage Field Research Articles

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.

Experimental Study on Evolution Law of Self-Magnetic Leakage Field during the Fatigue Process of Steel Weld

Experimental Study on Evolution Law of Self-Magnetic Leakage Field during the Fatigue Process of Steel Weld

Magnetic Signal Characteristics in Critical Yield State of Steel Box Girder Based on Metal Magnetic Memory Inspection

Metal magnetic memory testing (MMMT) is a nondestructive testing technique that can detect early signs of damage in components. Many scholars have studied the effect of uniaxial stress on the self-magnetic-leakage field (SMLF)’s strength. Nevertheless, there is still insufficient research on the combined action of bending and shear. We studied the law of distribution of the magnetic signal, ΔHSF(y), at different stress parts of a steel box girder and the quantitative relationship between the magnetic characteristic parameters and the external load. The results showed that the MMMT could accurately detect the early stress concentration zone (SCZ) and predict the final buckling zone of steel box girders. It could be judged that the corresponding parts of the steel box girder had entered the elastic-plastic working stage by the reverse change of the ΔHSF(y)-F and |HSF(y)|a -F curve trends, this feature could be used as an early warning sign before the steel box girder was deformed or destroyed. The fitted |HSF(y)|ave -F linear expression could be used as the expression between the magnetic signal and the shear capacity. All the evaluation methods were expected to provide a basis for effectively evaluating the stress state of steel box girders with the MMMT method.

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

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

Magnetic stray field mapping of stainless steel sheets using spin Hall magnetoresistance sensor

Recently, we have developed a spin Hall magnetoresistance (SMR) sensor featuring high-sensitivity, low-noise, zero-offset, and negligible hysteresis. Here, we demonstrate that the SMR sensor can be used to map the self-magnetic leakage field (SMLF) of stainless steel sheets. The SMLF serves as an effective knob for probing magnetism in steel sheets induced by either stress or composition inhomogeneity, which, in turn, affects its mechanical properties and corrosion resistance. However, the SMLF is typically quite weak, and thus the high-sensitivity and low-noise SMR sensor is uniquely suited for this application. The self-magnetic flux leakage mapping experiments have been conducted on SUS304 steel sheets with emphasis on the lift-off effect. Both analytical model and finite element modeling have been used to account for the experimental results. Although the SMLF mapping alone is unable to pinpoint the root cause of magnetism, i.e., whether it is due to stress or composition inhomogeneity, it does provide an efficient way for pre-screening of steel sheets to prevent defect formation at early stages.

Design and assembly of an apparatus system based on the Villari effect for detecting stress concentration zone on ferromagnetic materials

This paper presents the study results on the fabrication of a structural integrity assessment apparatus by determining stress concentration zones in pressure pipeline and equipment. The apparatus uses a triaxial magnetic field sensor to measure magnetic field components in three axes Ox, Oy, and Oz, in the working range of the magnetic field from -300 µT to 300 µT. The investigation of the selfmagnetic leakage field by this apparatus in the API 5L steel specimens under tensile stress shows a high variation of the magnetic field at a steel elongation lower than 1 mm (corresponding to the elastic deformation state of the material). In the case of an artificial defect, the apparatus can detect a change in the magnetic field caused by stress concentration.

Metal magnetic memory inspection of Q345B steel beam in four point bending fatigue test

The metal magnetic memory (MMM) method is a nondestructive testing method to inspect the early damage of steel structures. A four-point bending fatigue beam was inspected by this method during the whole fatigue life. The self-magnetic-leakage field (SMLF) values were measured during the test of the Q345B steel beam. Frequency of 3 Hz and stress ratio of 0.2 contributed to the fatigue life of 100,180 cycles. Test results indicate that both the normal and tangential component of the SMLF values can identify the stress concentration and the crack zones. The gradient can reflect the degree of damage. Furthermore, in order to study the change law of the SMLF values in the crack zone, an improved magnetic dipole model considering the crack dimensions and shape is proposed. The model predictions are in very good agreement with the corresponding test results. Lastly, three characteristic parameters, i.e. average ΔHp(y) field values, resultant magnetic field value H and magnetic parameter m, were extracted from the test data. These parameters can judge the fatigue stage and the damage degree of the specimen. Therefore, the research lays the experimental and theoretical foundation for using the MMM method to inspect steel structures under fatigue bending loads.

Metal Magnetic Memory Inspection of Q345 Steel Specimens with Butt Weld in Tensile and Bending Test

Metal magnetic memory (MMM) method is a non-destructive testing method based on the analysis of self-magnetic-leakage field (SMLF) distribution on components’ surfaces. The MMM method can determine stress concentration zones, imperfections, and heterogeneity in the microstructure of the material and in welded joints. In order to study the magnetization of defective and non-defective butt welded Q345 steel specimens under tensile and bending loads, the normal component of the SMLF (Hp(y)) field values were measured. The results demonstrate that Hp(y) field values and gradients are effective in capturing different stress states under tensile and bending loads. The distribution of Hp(y) field values for flexural tests are quite different from that of tensile tests. The gradient values can be used to determine the degree of stress concentration. In addition, three characteristic parameters were calculated. All three parameters can predict failures with early warnings. Specifically, whether the specimen is in tensile stress state or in compressive stress state can be distinguished by the average value of Hp(y) field area. The quality of the butt weld can be judged by the magnetic index (m). The judging criteria can be a significant complement to the inspection of welded joints using MMM method. Further research could help to validate the judging criteria and analyse the factors affecting the accuracy of the predictions.

The probabilistic analysis of fatigue crack effect based on magnetic flux leakage

In this paper, probabilistic analysis on the fatigue crack effect was investigated by applying the Metal Magnetic Memory (MMM) method, based on Self-Magnetic Leakage Field (SMLF) signals on the surface of metal components. The precision of MMM signals is essential in identifying the validity of the proposed method. The tension-tension fatigue test was conducted using the testing frequency of 10 Hz with 4 kN loaded, and the MMM signals were captured using the MMM instrument. As a result, a linear relationship was observed between the magnetic flux leakage and cyclic loading parameter, presenting the R-squared value at 0.72-0.97. The 2P-Weibull distribution function was used as a probabilistic approach to identify the precision of the data analysis from the predicted, and experimental fatigue lives, thereby showing that all points are placed within the range of a factor of 2. Additionally, the characteristics of PDF, CDF, failure rate and failure probability data analysis were plotted and described. Therefore, a 2P-Weibull probability distribution approach is determined to be an appropriate method to determine the accuracy of data analysis for MMM signals in a fatigue test for metal components.

Development of references of anomalies detection on P91 material using Self-Magnetic Leakage Field (SMLF) technique

This technical paper demonstrates the successful of the application of self-magnetic leakage field (SMLF) technique in detecting anomalies in weldment of a thick P91 materials joint (1 inch thickness). Boiler components such as boiler tubes, stub boiler at penthouse and energy piping such as hot reheat pipe (HRP) and H-balance energy piping to turbine are made of P91 material. P91 is ferromagnetic material, therefore the technique of self-magnetic leakage field (SMLF) is applicable for P91 in detecting anomalies within material (internal defects). The technique is categorized under non-destructive technique (NDT). It is the second passive method after acoustic emission (AE), at which the information on structures radiation (magnetic field and energy waves) is used. The measured magnetic leakage field of a product or component is a magnetic leakage field occurring on the component’s surface in the zone of dislocation stable slipbands under the influence of operational (in-service) or residual stresses or in zones of maximum inhomogeneity of metal structure in new products or components. Inter-granular and trans-granular cracks, inclusion, void, cavity and corrosion are considered types of inhomogeneity and discontinuity in material where obviously the output of magnetic leakage field will be shown when using this technique. The technique does not required surface preparation for the component to be inspected. This technique is contact-type inspection, which means the sensor has to touch or in-contact to the component’s surface during inspection. The results of application of SMLF technique on the developed P91 reference blocks have demonstrated that the technique is practical to be used for anomaly inspection and detection as well as identification of anomalies’ location. The evaluation of this passive self-magnetic leakage field (SMLF) technique has been verified by other conventional non-destructive tests (NDTs) on the reference blocks where simulated defects/anomalies have been developed inside at the weldment. The results from the inspection test showed that the signatures of magnetic leakage field gradient distribution prove that the peak is found on the location of defect/anomaly in the reference block. It is in agreement with the evidence of anomaly that seen in the radiography test film (RT).

Research on methods of defect classification based on metal magnetic memory

Metal magnetic memory (MMM) technique can evaluate early damages of ferromagnets and search possible defect locations, while just classifies the defect types roughly. To promote study in this area, the magnetic gradient tensor (MGT) of the self-magnetic leakage field (SMLF) on the fracture zone of crack and stress concentration was measured using a tri-axis magnetometer. From measured results, both the plane and the vertical characteristics of SMLF distributions were discussed. To remove the influence of the measuring direction on experimental results, a new parameter of the analytical signal of magnetic gradient tensor (AMGT) was introduced to determine the location and boundary of the defect. Then, the vertical features were acquired by measuring the plane distributions of AMGT under different lift offs. Through analyzing the vertical features, it was concluded that change rule of the maximum AMGT can be used to predict the defect type. At last, the explanation of the relationship between the vertical feature and the defect type was discussed, which can give some useful inspirations to researchers on magnetic leakage field testing.

Magnetic flux gradient observation during fatigue crack propagation: A case study of SAE 1045 carbon steel used for automotive transmission parts

The objective of this study is to evaluate the application of the metal magnetic memory (MMM) technique for investigations on fatigue crack propagation in a ferromagnetic material. Fatigue failure caused by stress concentration is serious in practical engineering. However, early fatigue damages cannot be detected by using traditional nondestructive testing (NDT) methods. Therefore this paper study about NDT method called metal magnetic memory (MMM) that has potentials for evaluating the fatigue damage at the early damage and critical fracture stages. While its capacity to evaluate the distribution of self-magnetic leakage field signals on the component’s surface is well-established, there remains a need to scrutinize the physical mechanism and quantitative analysis aspects of this method. To begin with, a fatigue test involving a loading of 7kN was conducted on a SAE 1045 carbon steel specimen. This material is frequently used in the manufacturing of automotive transmission components that include the axle and spline shaft. MMM signals were measured along a scanning distance of 100 mm and analysed during the propagation stage. Other than revealing that the value of the magnetic flux gradient signals dH(y)/dx increased in tandem with the crack length, the results also led to the detection of the crack growth location. It was anticipated that the dH(y)/dx value will also exhibit an upward trend with a rise in the fatigue growth rate of da/dN . A modified Paris equation was utilized to correlate dH(y)/dx with da/dn through the replacement of the stress intensity factor range Δ K . This resulted in the log-log plot of da/dN versus dH(y)/dx portraying an inclination similar to the log-log plot of da/dN versus Δ K . A linear relationship was established between dH(y)/dx and Δ K with the R2 value as 0.96. Players in the automotive industry can benefit from the disclosure that dH(y)/dx can effectively replace Δ K for the monitoring of fatigue crack growth behaviour.

Theoretical research on the characteristics of the self-magnetic leakage field induced by ferromagnetic pipelines

Theoretical research on the characteristics of the self-magnetic leakage field induced by ferromagnetic pipelines

Assessment of welded joints stress–strain state inhomogeneity before and after post weld heat treatment based on the metal magnetic memory method

The results of welding specimens’ stress state studies before and after post weld heat treatment (PWHT) based on the metal magnetic memory (MMM) method are presented. The relationship between variation of the welded joint’s stress state and the intensity of the self-magnetic leakage field formed during welding under the action of a weak geomagnetic field is shown. Quick detection of welded joints stress state inhomogeneity zones by the MMM method and assessment of their variation after PWHT is proposed.

Investigating the fatigue failure characteristics of A283 Grade C steel using magnetic flux detection

The Metal Magnetic Memory (MMM) method is a non-destructive testing method based on an analysis of the self-magnetic leakage field distribution on the surface of a component. It is used for determining the stress concentration zones or any irregularities on the surface or inside the components fabricated from ferrous-based materials. Thus, this paper presents the MMM signal behaviour due to the application of fatigue loading. A series of MMM data measurements were performed to obtain the magnetic leakage signal characteristics at the elastic, pre-crack and crack propagation regions that might be caused by residual stresses when cyclic loadings were applied onto the A283 Grade C steel specimens. It was found that the MMM method was able to detect the defects that occurred in the specimens. In addition, a justification of the Self Magnetic Flux Leakage patterns is discussed for demonstrating the effectiveness of this method in assessing the A283 Grade C steel under cyclic loadings.

Non-destructive evaluation of the damage of ferromagnetic steel using metal magnetic memory and nonlinear ultrasonic method

Based on the measurement of residual magnetic spontaneous stray field, metal magnetic memory (MMM) technique is an effective method in evaluating the degree of early damage for ferromagnetic materials due to the existence of stress concentration. In this paper, the normal and tangential components of the stress induced self-magnetic leakage field (SMLF) intensity on the surface of specimens were measured at predetermined tensile forces throughout the tensile process. The results show that the stress induced normal and tangential components of the self-magnetic leakage field are effective in characterizing different stress levels in elastic deformation stages; and the tangential component is more effective in characterizing different plastic deformation stages. Furthermore, experimental measurements using nonlinear ultrasonic technique (NUT) were also conducted at the same stress level when the magnetic memory signals were collected. It shows that MMM technique is ef- fective in charactering the stress-strain state in elastic deformation stage for ferromagnetic materials; and NUT is effective in charactering the degree of plastic deformation.

Modelling and analysis of magnetic memory testing method based on the density functional theory

Metal magnetic memory (MMM) method is a novel, passive magnetic method for inspecting mechanical degradation of ferromagnetic components. To promote a further understanding of the MMM testing mechanism, the relationship between stress concentration and the self-magnetic leakage field measured by MMM effect was quantitatively interpreted using a density functional theory based on the generalised gradient approximation. Meanwhile, the influence of doping effect on MMM signal was calculated. Interestingly, the theoretical approach is in very good agreement with the experimental observations. A new research programme for quantitative interpretation of the MMM effect was initiated.

Self-magnetic-leakage field detection using magneto-optical sensor technique

Measurement of spontaneous magnetic stray field signals has been reported to be a promising tool for capturing macro-scale information of deformation states, defects and stress concentration zones in a material structure. This paper offers a new method for self-magnetic leakage field detection using a magneto-optical (MO) hand-held microscope. Its sensor has a dynamic field range between ±0.05 and ±2 kA/m and a lateral optical resolution of approx. 10 μm. We examined flat tensile test specimens of metastable austenitic steel AISI 304. Static tensile tests were repeatedly interrupted at various predetermined states of strain and the magnetic information was measured by the MO system. Comparative measurements using a high-precision magnetic field GMR-sensor, verify the outstanding capability of the MO microscope regarding spatial resolution of magnetic fields.

The quantitative interpretation by measurement using the magnetic memory method (MMM)-based on density functional theory

The paper demonstrates the relationship between a local stress concentration state and the self magnetic leakage field (SMLF) measured by the metal magnetic memory (MMM) effect using a first-principle calculation based on the density functional theory (DFT). In order to verify the theoretical approach, blasting experiments with X70 steel pipes were performed to document the reliability of the investigation methods. Interestingly concerning the theoretical approach is the linear change of the local SMLF signal with the increase of stress which is in very good agreement with the experimental observations. A new research program for quantitative interpretation of the MMM effect was initiated.