Abstract
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.
Highlights
Many types of equipment manufactured with ferromagnetic materials in service are working under the condition of stress corrosion
It was used to investigate the corrosion behavior of mild steel (Q235) [10], and Wang reported that pitting corrosion of high strength steel is quantitatively evaluated by combining 3-D measurement and image-recognition-based statistical analysis [11]
The previous study [40] showed that the ambient stress conditions during corrosion defect formation would affect the Magnetic Flux Leakage (MFL) signals based on magnetic flux leakage testing
Summary
Many types of equipment manufactured with ferromagnetic materials in service are working under the condition of stress corrosion Most of this equipment is susceptible to corrosion defects. The non-destructive testing of stress corrosion defects has been widely studied, the traditional NDT methods have some limitations. MMMT technology is used to diagnose the early damage by measuring the self-magnetized leakage field on the surface of ferromagnetic materials [25,26]. The impact of stress or strain on Magnetic Flux Leakage (MFL) signals of ferromagnetic materials has been researched for assessing stress concentration [35,36] and fatigue damage [37,38,39]. The previous study [40] showed that the ambient stress conditions during corrosion defect formation would affect the MFL signals based on magnetic flux leakage testing. The feasibility of evaluating the degree of corrosion of ferromagnetic materials using the MFL signals was discussed
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