Evolution of the Stress-Induced Residual Magnetic Field of X70 Pipeline Steel With Multiple Corrosion Defects

2021 ◽  
Author(s):  
Sheng Bao ◽  
Qiang Luo ◽  
Zhengye Zhao ◽  
Jian Yang
Keyword(s):  
Magnetic Field ◽  
Pipeline Steel ◽  
Normal Component ◽  
Tangential Component ◽  
Magnetic Memory ◽  
X70 Pipeline Steel ◽  
Corrosion Defect ◽  
Residual Magnetic Field ◽  
Corrosion Defects ◽  
Ferromagnetic Steels

Abstract The aim of this research is to investigate the correlation between the residual magnetic field (RMF) and multiple corrosion defects in ferromagnetic steels. Specimens of X70 pipeline steel were machined into standard bars with a single corrosion defect, double corrosion defects and triple corrosion defects, respectively. Tensile tests were carried out to detect the RMF signals on the surface of these specimens. The variations of abnormal magnetic changes of the RMF signals with the external loads were investigated and the results showed that the tangential component and the normal component of the RMF signals of three defect patterns presented different shapes. It was found that the RMF signals were capable of capturing the location and the number of defects in pipeline steels. The peak values of the tangential component and the slopes of the normal component were not influenced by the defects number. This research will promote the investigation on the corrosion defect cluster of ferromagnetic steels based on the metal magnetic memory (MMM) technique.

Correlation Between Stress Concentration Degree and Residual Magnetic Field

2016 ◽  
Author(s):  
Sheng Bao ◽  
Ashri Mustapha ◽  
Huangjie Lou
Keyword(s):  
Magnetic Field ◽  
Stress Concentration ◽  
Tensile Tests ◽  
Magnetic Memory ◽  
Metal Magnetic Memory ◽  
Residual Magnetic Field ◽  
Concentration Degree ◽  
Qualitative Relationship ◽  
Ferromagnetic Steels

In this research, the correlation between the stress concentration degree and the residual magnetic field (RMF) of ferromagnetic steels is investigated. Tensile tests were carried out to measure the RMF signals on the surface of steel specimens with different stress concentration degrees. The effectivity of the metal magnetic memory (MMM) technique in defective specimens was investigated in comparison with a non-defective specimen. Analysis of the qualitative relationship between the stress concentration degree and the RMF components was subsequently performed on two types of defective specimens. The qualitative correlation between the planar distributions of the RMF components and the stress concentration degree was further studied. It was validated that both the RMF signal and its planar distribution are effective in characterizing the stress concentration degree. The results obtained in this research will be a complement to the MMM technique.

Field Topography of Defects in Magnetic Non-Destructive Testing

NDT World ◽  
2015 ◽  
Vol 19 (4) ◽  
pp. 53-56
Author(s):  
Покровский ◽  
Aleksey Pokrovskiy ◽  
Новиков ◽  
Ilya Novikov ◽  
Хвостов ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Fault Location ◽  
Extreme Values ◽  
Accurate Determination ◽  
Normal Component ◽  
Tangential Component ◽  
Destructive Testing ◽  
Hall Sensors

The defect parameters can be evaluated by defect induced magnetic field topography using Hall sensor. Investigations were carried out on specially prepared samples with artificial defects. According to calculations and tests tangential component of magnetic field strength extremes were detected values on either side of the defect in the surface layer l only. But this effect can not be detected by Hall sensors or Foerster probes due to their sizes. The normal component of the magnetic field strength provides a sufficiently accurate determination of the fault location, where this component becomes zero between the two extreme values located quite close to each other. The results of the study showed that at distances available to Hall transducers one can confine to the experimental research, whereas computational methods shall be used to study the topography of field defects at very small distances from the surface. This could open the prospects for testing at small distances from the surface of the object.

scholarly journals Application of Metal Magnetic Memory Testing Technology to the Detection of Stress Corrosion Defect

2020 ◽  
Vol 10 (20) ◽  
pp. 7083
Author(s):  
Bingxun Zhao ◽  
Kai Yao ◽  
Libo Wu ◽  
Xinglong Li ◽  
Yue-Sheng Wang
Keyword(s):  
Stress Corrosion ◽  
Normal Component ◽  
Ferromagnetic Materials ◽  
Error Rates ◽  
Magnetic Memory ◽  
Memory Testing ◽  
Metal Magnetic Memory ◽  
Corrosion Defect ◽  
Detection Of Stress ◽  
Metal Magnetic Memory Testing

The damage of equipment manufactured with ferromagnetic materials in service can be effectively detected by Metal Magnetic Memory Testing (MMMT) technology, which has received extensive attention in various industry fields. The effect of stress or strain on Magnetic Flux Leakage (MFL) signals of ferromagnetic materials has been researched by many scholars for assessing stress concentration and fatigue damage. However, there is still a lack of research on the detection of stress corrosion damage of ferromagnetic materials by MMMT technology. In this paper, the electrochemical corrosion system was designed for corrosion experiments, and three different experiments were performed to study the effect of corrosion on MFL signals. The distribution of MFL signals on the surface of the specimen was investigated. The results indicated that both the normal component Hn and tangential component Ht of MFL signals presented different signal characteristics when the specimen was subjected to different working conditions. Finally, two characterization parameters, Sn and St, were defined to evaluate the corrosion degree of the specimen, and St is better. The direct dependence of corrosion depth on the parameter was developed and the average error rates between the predicted and measured values are 8.94% under the same working condition. Therefore, the expression can be used to evaluate the corrosion degree of the specimen quantitatively. The results are significant for detecting and assessing the corrosion defect of ferromagnetic materials.

Characterization of Crack Initiation Life in Ferromagnetic Material by Metal Magnetic Memory Testing

2015 ◽  
Vol 817 ◽  
pp. 791-796
Author(s):  
Chang Liang Shi ◽  
Wei Xue Tang ◽  
Hao Zhan ◽  
Shi Yun Dong
Keyword(s):  
Magnetic Field ◽  
Crack Initiation ◽  
Normal Component ◽  
Ferromagnetic Material ◽  
Magnetic Memory ◽  
Memory Testing ◽  
Metal Magnetic Memory ◽  
Numerical Fitting ◽  
Crack Initiation Life ◽  
Metal Magnetic Memory Testing

In the geomagnetic field, stress can induce spontaneous magnetic signals in ferromagnetic materials, the method, named metal magnetic memory testing, can be potentially applied in estimating the fatigue life. In this paper, the normal component of magnetic field, Hp (y), was measured during dynamic tension test on the surfaces of ferromagnetic specimens with stress concentration factor of 5. The results indicated that the gradient of magnetic field intensity, K, was the key parameter to characterize crack initiation life. Then the numerical fitting of K and fatigue cycles were done under three level loads, 568.7MPa, 698.8MPa and 864.4MPa, meanwhile, a simple model was derived.

Quantitative Stress Evaluation and Defect Identification in Ferromagnetic Steels Based on Residual Magnetic Field Measurements

2021 ◽  
Vol 79 (3) ◽  
pp. 311-319
Author(s):  
S Bao ◽  
M Fu ◽  
Z Zhao ◽  
P Jin
Keyword(s):  
Magnetic Field ◽  
Applied Load ◽  
Quantitative Characteristic ◽  
Ferromagnetic Material ◽  
Tensile Tests ◽  
Load Level ◽  
Characteristic Parameters ◽  
Defect Identification ◽  
Residual Magnetic Field ◽  
Ferromagnetic Steels

In this paper, the correlation between the residual magnetic field (RMF) and the applied load is investigated. Tensile tests were carried out to measure RMF signals on the surface of 30CrNiMo8 steel specimens with three types of machined defect shapes. Results show that the RMF curves of the three different defective specimens demonstrate similar overall evolution patterns during the loading process, while the magnetic signals exhibit noticeable differences in the defect area. It suggests that the profiles of the stress-induced RMF curves are strongly dependent on the defect’s shape, notch width, and load level. An improved method is proposed to extract some quantitative characteristic parameters from the magnetic signals. The characteristic parameters that reflect the fluctuation degree are in quadratic polynomial relation with the applied load, which can be potentially used to evaluate the applied load acting on a ferromagnetic material with a macro defect. The characteristic parameters that reflect the acting range seem to be independent of the applied load, and the normal ones are capable of capturing the defect’s location and shape. This paper presents a supplement for quantitative defect identification for discontinuities in ferromagnetic steels by RMF measurements.

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