Investigation of Metal Magnetic Memory for Stress State Identification in Steel Components

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Conventional magnetic inspection technologies require direct application of magnetizing flux to ferromagnetic components to**generate magnetic flux leakage (MFL) signals from defects or for the detection of stress. Applications of such technologies to the**inspection of large volumes of material are time consuming and costly. Magnetization techniques are also limited in the case of**inspection of irregular structures. Metal magnetic memory (MMM) method is a potential alternative inspection technology that may**be used to identify stress in steel components. For example, it can be used in pipelines, where stress concentrations arise near**pits, localized plastic deformation, or due to ground settling or slippage. The induced stresses produce conditions that may lead to**stress corrosion cracking. MMM is a passive technique that uses the magnetization of the earth's magnetic field in combination**with other potential factors to assess the stress state of the part. MMM is based on magnetoelasticity (Villari effect). It is a rapidly**expanding method for the detection of anomalies in magnetic fields at the surface or near ferromagnetic components due to local**changes in their stress state. MMM can be used to determine the location of pipe from above ground and has potential to assess**the stress state of pipe utilizing inexpensive magnetic sensor arrays. Improved technology coupled with a better understanding of**the physical basis of MMM could lead to simple monitoring capabilities and, hence, improved service life and performance of**infrastructures such as water/wastewater and gas/oil pipelines, turbines, pressure vessels, rails, welded and casting parts.**