Advances in Carbon Steel Weld Inspection using Tangential Eddy Current Array

摘要

The inspection of carbon steel welds for surface cracks remains a significant inspection challenge. Established methods such as penetrant testing (PT) and magnetic particle inspection (MPI) are effective but lack practicality. The conventional eddy current inspection technique (ECT) represents an opportunity for improvement, however using a single coil ECT pencil probe results in protracted inspection times and results are adversely affected by material properties and geometry. Eddy current array (ECA) probes have always represented the ideal solution but, until recently, have been limited to non-ferrous materials or detection only in ferrous materials. However, recent advances in ECA coil design and multiplexing patterns have contributed to the development of a new generation of ECA probes for carbon steel weld inspections. The main objective behind the development of these new Tangential ECA (TECA) probes was to determine the optimal set of parameters for the probes to obtain a clear discrimination between surface breaking defects, lift off and permeability changes while still being able to monitor and quantify each signal individually. By multiplexing and leveraging advanced data processing capabilities, this ECA solution allows inspections to be carried out (a) quickly (b) with accurate depth sizing of cracks and (c) without the need to remove protective coatings. This new approach offers additional benefits such as state-of-the-art imaging (e.g. 2D and 3D C-scan displays), improved surface coverage and ease of data archiving. Furthermore, the new sensor and technique developed allows inspections to be carried out under the mainstream ECT certification. This paper describes the concept of tangential eddy current array, supported with a recent Probability of Detection (PoD) study and inspection results obtained from various trials and in-service examinations. Comparisons are made against alternate methods and conclusions are drawn as to the benefits of tangential eddy current array in the context of carbon steel weld examinations.