Research on harmonic eddy current magnetic field detection of buried steel pipeline

Harmonic eddy current magnetic field inspection, as one of pipeline nondestructive inspection technology, can be accurately and efficiently used to estimate the damage of buried steel pipeline. Based on the principle of harmonic eddy current magnetic field detection, a theory model of double frequencies alternating excitation was established, and a non-contact coil array detection probe was also designed. An indoor experimental platform was built to proceed experimental study on the differences in magnetic induction intensity distribution for various pipeline defect species, and the variation in magnetic induction intensity for different excitation frequencies and input voltages. Results showed that change in resistivity due to the pipeline defect causes a nonuniform current distribution that distorts the induced magnetic field, resulting significant increase in the magnetic induction intensity; While moving the probe along the surface of the pipeline, better detection results can be achieved for various defect species with greater defect depth and smaller angular orientation between defect trend and moving direction; Similarly a robust change in the magnetic induction intensity can be observed with low signal frequency of harmonic power supply and greater input voltage of detection probe. The researches done prove that harmonic eddy current magnetic field inspection can effectively realize the nondestructive damage detection of buried steel pipeline.