Table 1.

Comparison of common defect-detection methods.

Methods	Strengths	Weaknesses	Applicable
Ultrasonic testing [45]	Easy to use, strong penetration, high sensitivity, portable equipment, and automatic detection.	Unsuitable for complex workpieces.	Any material
Machine vision detection [51]	A wide range of applications, high precision, remains unaffected by the profile of the detection piece, and automatic detection.	Detects surface defects only.	Any material
Magnetic powder testing [57]	The position, shape, and size of the defect can be visualized, which is suitable for any size of workpiece detection. It has the characteristics of high precision and low cost.	Application is limited to ferromagnetic materials. Detection results are affected by the geometric shape of the test pieces. Realizing automatic detection is difficult.	Ferromagnetic materials (e.g., cast steel, pipe, calendar, bar, etc.)
Osmosis testing [58]	Free from the influence of material type and shape profile and high sensitivity to pinhole defects.	Detecting porous materials is difficult, and the detection speed is slow. Detection results are greatly affected by the inspectors, and automatic detection is difficult to carry out.	Nonporous materials are tested (e.g., metal casting, ceramic, plastic, glass, etc.)
Eddy current testing [59]	Noncontact detection, fast detection speed, high sensitivity, and suitable for high-temperature environments, automatic detection.	The shape and size of the defects cannot be visualized. The applicable materials are limited. Difficulty in detecting deep defects with low detection accuracy.	Conductive or non-metallic material (e.g., workpieces, pipes, wires, and graphite)
X-ray testing [60]	Non-destructive detection, strong penetration, free from the influence of material appearance and structure, and easy operation.	Radiation effects for the staff involved in the detection.	Any material