A Drill Pipe Thread Detection System Based on Alternating Current Field Measurement

Abstract

Drill pipe threads, as critical structural components connecting drill pipes, are subjected to harsh downhole environments and complex loads. They are prone to defects such as cracks, galling, wash-out, and other failures, which compromise the safety of drilling operations. To address the inspection requirements for drill pipe threads, this paper proposes a defect inspection system based on alternating current field measurement (ACFM) technology. Using Maxwell simulation software, we analyzed the influence of the bottom geometry of the magnetic core leg on the characteristic magnetic field signals of defects and optimized the magnetic core structure. Furthermore, the influence of varying crack lengths and depths on the detection signals was systematically investigated. The results reveal the mapping relationship between the signal features and the defect dimensions, providing a basis for quantitative inversion. Subsequently, the inspection device was designed, a prototype was manufactured, and the complete system was established. The performance of the system was evaluated using drill pipe joints containing defects at the thread tooth crest, thread tooth side, and thread tooth root. The results demonstrate that the system can effectively identify defects at various positions along the drill pipe thread, verifying its reliability.