Abstract: In order to solve the problem that the conventional inspection method for the liquid ammonia pipelines in the coating of the ammonia refrigeration system in service was difficult to carry out, a real-time imaging detection method based on X-ray digital imaging was proposed to detect the defects of the pipelines in the service stage. The double action of coating and medium affected the quality of X-ray and the defect recognition of digital image. Through the optimization of radiography technology and experimental verification, it was shown that the corrosion site coincided with the detected image, the method can judge the defect and corrosion status in real time. The nondestructive testing, corrosion testing, undercut and wrong edge inspection of the weld line of the liquid ammonia pipeline with coating layer were helpful to find out the problem and eliminate the hidden trouble in time, so as to realize the safe operation of the pipelines.