Pulsed eddy current testing of corrosion in pipes under insulation

What is it about?

Pulsed eddy current (PEC) testing has attracted widespread attention because of its unique advantages in detecting local defects in insulated pipes. In this paper, rectangular, U-shaped and semicircular PEC focusing probes are designed, the magnetic energy utilization efficiency and focusing properties of the developed probes are simulated and compared, and their detection sensitivities are experimentally compared. The magnetic flux through specific surfaces is calculated to calculate the utilization of magnetic energy by the different probes, and the eddy current dissipation power is used to quantitatively describe the eddy current field focusing properties of various types of probes. The simulation results show that the magnetic field energy utilization efficiency of the semicircular focusing probe is significantly higher than that of the other two probes, but the eddy current field distributions of the three probes are similar, and the focusing properties are not significantly different. The experimental results show that the three types of PEC probes can effectively detect local defects under a certain lift-off. By calculating the detection sensitivity of different probes to defects under different lift-off conditions, it is determined that the detection sensitivity of the semicircular probe is significantly higher than that of the U-shaped probe and rectangular probe. The experimental results are consistent with the numerical simulation results. The research results are conducive to the optimal design of PEC focusing probes for insulated pipes.

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Why is it important?

Insulated pipes are commonly used in the petroleum, natural gas, and chemical industries and in other fields. They are used to transport high-temperature and high-pressure or corrosive gas–liquid media, which are prone to corrosion defects, mainly local corrosion defects[1-2]. It is difficult to detect the inner and outer wall corrosion of insulated pipes. Pulse eddy current testing (PECT) is a noncontact testing method. Compared with traditional eddy current testing, PECT adopts square wave excitation. It has advantages including a large penetration depth of the incident electromagnetic field, a strong ability to detect the defect depth, and detailed detection information. Therefore, the application of PECT in the detection of corrosion of insulated pipes has attracted widespread attention.

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