Abstract
Stress and deformation are important factors that affect the safe operation of pipelines. Plastic deformation in the pipeline indicates a state of critical damage. Based on micro-magnetization and stress equivalent magnetic field theories, the change mechanism of ferromagnetic materials under external stress is analyzed. The 3D simulation model of the iron–carbon alloy system is established by the Material Studied software, and the relationship between the system magnetism and stress is obtained by calculating the electronic spin state distribution changes under different stress applications. The pipeline suppression experiment is designed to study the change characteristics of the magnetic induction intensity on the pipeline surface during the repeated suppressions until yield. Results show that the weak magnetic signal continuously varies as the pressure on the pipeline increases. The greater the pressure, the lower the magnetic induction intensity on the pipe surface. The pipeline exhibits different weak magnetic signal characteristics in the elastic and plastic deformation stages. The magnetic signal variation curve has apparent inflection points. The deformation and damage states of the pipeline can be assessed by the change characteristics of the weak magnetic signal. Repeated suppression causes the pipeline magnetism to weaken and the initial magnetization of the material to decrease. The experimental results are consistent with the theoretical analysis.
Highlights
Ferromagnetic pipelines are the main transportation mode of important energy and media in the world, and their applications cover various fields such as energy, equipment, and engineering production
Due to its running characteristics and work environment, oil and gas pipelines have characteristics of high pressure, flammability, explosion, and corrosion, which determine the importance of its safety management
When the ferromagnetic material is magnetized by an external magnetic field, the domain structure and its corresponding spontaneous deformation change, which results in the magnetostrictive effect
Summary
Ferromagnetic pipelines are the main transportation mode of important energy and media in the world, and their applications cover various fields such as energy, equipment, and engineering production. Magnetic memory testing can characterize the stress concentration degree of the ferromagnetic material by detecting the irreversible magnetic field change characteristics on the material surface after the stress application in the geomagnetic environment [6]–[9]. On the basis of magnetic memory, weak magnetic detection is proposed to assess the stress concentration degree by detecting the weak magnetic field signal distribution and variation characteristics on the pipeline surface under the non-excitation state (earth magnetic field environment) [10]–[13]. This method is an online detection technology for pipeline stress concentration [14]–[16]. The foundation of weak magnetic detection technology for early damage stage of oil and gas pipelines is established
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