# Application of Metal Magnetic Memory Testing Technology to the Detection of Stress Corrosion Defect
## 5 Conclusions  
In this paper, static tensile experiments, corrosion experiments without and after loading were performed to study the effect of corrosion on MFL signals. The normal and tangential components of the MFL signals, namely \(H_{\text{n}}\) and \(H_{\text{t}}\) were measured using the 3D MFL detection system, and the distribution regularity of them during the corrosion process was investigated. The following conclusions are obtained:  
1. The normal and tangential components of the MFL signals in corrosion experiments without and after loading presented a \"trough-peak\", and \"peak\" shape, respectively. It is known from experimental results that when the specimen was corroded without and after loading, the normal and tangential components both showed the same signal characteristics, and a more substantial amplitude value could be found in the corrosion experiment after loading.
2. The normal and tangential components of the MFL signals in the static tensile experiment presented a \"peak-trough\", and \"trough\" shape, respectively. It is found that the normal and tangential components showed different signal characteristics under different working conditions: When the specimen was subjected to tensile load and corroded, respectively, the normal and tangential components both exhibited opposite signal characteristics. According to the analysis, the critical reason for different signal characteristics is that the leakage magnetic field \(H_{\text{c}}\) generated at the defect after the specimen has been corroded is opposite to the leakage magnetic field \(H_{\text{m}}\) caused by force.
3. The characterization parameters of MFL signals, \(S_{\text{n}}\) and \(S_{\text{t}}\), are capable of evaluating the corrosion degree of the specimen, and \(S_{\text{t}}\) is better. The characterization parameter of the tangential component of the MFL signals is more sensitive to the corrosion, which is different from the traditional research results on the MFL signals caused by stress where the characterization parameter of the normal component of the MFL signals is more sensitive to the force. The direct dependence of corrosion depth (\(h\), theoretical) on the parameter \(S_{\text{t}}\), \(h\), theoretical \(=f(S_{\text{t}})\) 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.  
Figure 16: Comparison between measured and theoretical values of the corrosion depth \(h\).  
**Author Contributions:** Conceptualization, K.Y.; Data curation, X.L.; Formal analysis, B.Z.; Funding acquisition, K.Y.; Investigation, B.Z.; Methodology, B.Z.; Project administration, Y.-S.W.; Resources, X.L.; Supervision, L.W.; Validation, L.W.; Visualization, B.Z.; Writing-original draft, B.Z.; Writing-review & editing, K.Y. and Y.-S.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Fundamental Research Funds for the Central Universities (2019 JBM82) and the National Natural Science Foundation of China (No. 11872104).  
**Conflicts of Interest:** The authors declare no conflict of interest.