Abstract: Online detection is carried out for the cracks on the outer surface of the hydrogen production adsorption tower. Since the medium is flammable and explosive, it is not advisable to perform large-area hot work for paint removal by grinding. Conventional nondestructive testing methods are difficult to implement, and array eddy current testing is prone to miss detecting tiny cracks due to the influence of the paint layer thickness. Aiming at this problem, this paper studied the influence of the lift-off effect of the paint layer thickness on the accuracy of array eddy current testing and the characteristics of acoustic emission signals of tiny cracks under three-point bending loads. Online array eddy current testing was carried out for the cracks under the paint layer of the adsorption tower, and the acoustic emission testing process was formulated as a supplementary means. In the on-site application, multiple cracks were detected by array eddy current testing on a certain adsorption tower. After the defects were eliminated, no abnormality was found by acoustic emission testing, and there was no leakage again during the five years of operation. The combined testing scheme proposed in this paper ensured the safe and stable operation of the hydrogen production unit and provided references for online non-grinding detection of fatigue cracks.