Detecting Multi-directional Cracks on Catalyst Tubes of Reformer Furnace using a Saturated Low-Frequency Eddy Current Array

This paper describes the demonstration experiment of detecting multidirectional cracks in the catalyst tube of a reformer furnace using a saturated low-frequency eddy current array (SLFEC). The experiment focused on detecting and sizing the machined (EDM) flaws in multidirectional (axial and transverse) and in both internal (ID) and outer diameters (OD) of the sample tube. Based on the experiment results, SLFEC testing showed good results as an inspection method for finding cracks in the catalyst tube and some limitations presented by poor detectability in Crack–Notch with less than 25% from the ID surface. The material properties could impact the test result, as the magnetic permeability affects the penetration of eddy current permeability variations and could cause false indications. The magnetic permeability can be suppressed by utilizing a permanent magnet to saturate the material partially. The penetration improves by decreasing the eddy current frequency impacting the detection sensitivity of near-surface flaws, where the high frequency will give better near-surface detection and resolution. Multi-frequencies provide an optimum solution for overall detection in a single scan.