Study on Remote Magnetic Detection Technology for External Defects of Small-Diameter Pipelines

Abstract

Nonpiggable multiproduct pipelines lack effective methods for detecting the pipe’s external defects (PEDs). Therefore, a pipeline remote magnetic detection (PRMD) technology for buried small-diameter pipelines was developed, which can achieve trenchless detection of PEDs. In this paper, an external pipe defect remote detection model is established to reveal the features of the three-dimensional magnetic gradient signal of PEDs. The quantitative relationship between the magnetic gradient modulus and defect depth was analyzed, and the influence of some factors was obtained. Furthermore, a PRMD method was established to detect a 3.56-km buried small-diameter multiproduct pipeline. The diagnostic indicator Fd based on the magnetic gradient modulus is proposed to determine damage levels of defective pipes, which was validated by the excavation inspection results. The results show that the magnetic gradient modulus G reaches a peak at PEDs. The maximum magnetic gradient modulus Gmax has an exponential relationship with the defect depth. Finally, 10 Level II defects and 19 Level III defects were found in the 3.57-km buried pipeline.