High Lift Value Metal Pipeline Detection Model Based on Metal Magnetic Memory 3-D Differential Method

The metal magnetic memory (MMM) nondestructive testing (NDT) method is widely accepted for its strong environmental adaptability, high sensitivity, and simple measurement operation; nevertheless, due to the complex environmental factors and the influence of detection distance, it is still a technical challenge to perform high-accuracy pipeline inspection at high lift-off values, where the lift-off value is the distance between the magnetic probe and the surface of the pipe. To better study the MMM field model, this article puts forward the high lift-off distance MMM–3-D (HDMMM-3-D) differential method of ${G}_{z}$ . Through the COMSOL software simulation of the finite element method, we performed practical tests with the low-noise acquisition equipment in an independent design. The finite element method simulation and the results of the numerical, analytical image features and numerical sizes are similar. In the field pipeline test, the waveform signal undergoes a change of first rising and then falling at the damage location; comparing the waveform of magnetic gradient and ${G}_{z}$ at the 3 m damage location of the pipeline, the ${G}_{z}$ has a more detailed differentiation of the number of damages, and the peak size of the damage signal is more obvious. It is effective to verify the HDMMM-3-D differential method, which provides the theoretical basis and application support for the in-depth study of high separation value in the field of nondestructive testing.