Novel semi-ring type alternating current field measurement probe for inspection of coiled tubing

Coiled tubing is a critical equipment in the oil and gas exploration and development field. Due to the high pressure, corrosive medium and repeated buckling, cracks are easily introduced in the surface of the coiled tubing. It is necessary to detect cracks in-service for the maintenance of the coiled tubing. In this paper, a new semi-ring type alternating current field measurement (ACFM) probe is presented for imaging and evaluating the surface cracks in the coiled tubing. The finite element method (FEM) model is developed to analyze the characteristic signals of the crack. According to the simulate results, the tunnel magneto resistance (TMR) sensor arrays in semi-ring ACFM probe is placed between the coiled tubing wall and the coil. The experimental results show that the novel ACFM probe can achieve imaging and detection of surface axial and circumferential cracks in the coiled tubing. The through-wall crack can be judged effectively compared to the shallow crack. The length of axial cracks can be accurately evaluated by the peak-valley spacing of the Bz signal. The length of circumferential crack can be evaluated approximately by the location of sensor arrays in the circumferential direction.