Research on Eddy Current-Based Detection Method for Ultimate Tensile Strength of Pipelines

The accurate assessment of the ultimate tensile strength (UTS) of pipeline materials is crucial for determining the maximum allowable operating pressure of pipelines and predicting potential locations of structural failure. To evaluate the UTS of in-service pipelines, this study investigated the relationship between the UTS of steel and its magnetic permeability based on dislocation dynamics and density functional theory. An eddy current-based detection method for assessing the UTS of pipelines was proposed. The effectiveness of the proposed method was verified through experiments, and the impact of temperature variations and surface corrosion on the detection outcomes was also investigated. The experimental results demonstrate that when the detection frequency is set within the range of 5–50 kHz, the eddy current testing results of Q235 and Q345 steels exhibit an approximately linear distribution on the impedance plane, corresponding to the ascending order of their UTS. The optimal detection frequency for both steel types is identified to be between 10 and 50 kHz. Within this frequency range, both the amplitude and the phase angle of the eddy current impedance display an approximately linear correlation with the UTS of the materials. Under linear regression analysis, the Pearson correlation coefficient between impedance amplitude and UTS exceeds 0.75, while that between phase angle and UTS remains above 0.7. This method exhibits less susceptibility to temperature variations and surface corrosion on steel, making it suitable for complex working conditions, including internal inspection of pipelines.