Definition
Paint leakage detector is an electronic instrument used to identify discontinuous areas on the coating surface, mainly to detect defects such as missing coating, pinholes, and pores caused by insufficient or complete absence of coating thickness. It evaluates coating integrity in a non-destructive way and is widely used in anti-corrosion engineering, industrial manufacturing, ship and bridge maintenance, and other fields to ensure that coatings achieve the desired protective properties.
Principle
The instrument works on the principle of high voltage discharge or low voltage resistance. The high-voltage detector applies high voltage between the probe and the substrate, and when the probe passes through the coating defect, the current breaks through the air to form a path, triggering an audible and visual alarm. The low-voltage type measures the change in resistance between the probe and the conductive substrate to determine the defect, and is suitable for thin layers or sensitive coatings. Both methods rely on the difference in conductivity at the coating defect to detect it.
Measurement method
Before measurement, the appropriate voltage or sensitivity level should be selected according to the coating thickness, substrate type and environmental conditions. During operation, the probe scans the surface under test at a constant speed of about 0.3 m/s to maintain stable contact between the probe and the coating surface. When a defect is found, the instrument immediately alarms, marks the location and records the data. After the measurement, the instrument needs to be calibrated and verified to ensure that the test results meet the requirements of relevant standards such as ISO 2746 or ASTM D5162.
Influencing factors
The uniformity of coating thickness directly affects the detection sensitivity, and too thick or too thin may cause false alarms. When the ambient humidity is high, surface moisture may interfere with electrical signal conduction. Insufficient cleanliness on the surface of the substrate, such as the presence of dust or grease, will form a false alarm. Uneven operator movement speed or probe angle offset can also cause test results to be biased. In addition, a weak instrument battery can reduce output stability.
Applications
The instrument is suitable for the inspection of anti-corrosion coatings on the inner walls of tanks and can detect potential leaks in the welds. In the evaluation of the anti-corrosion layer outside the pipeline, it can quickly locate the damaged area generated during transportation. Inspection of ship ballast tanks and deck coatings helps prevent the spread of corrosion in the marine environment. In the maintenance of steel bridge coatings, it can be used to regularly monitor the aging condition of the coating. In the automotive industry, it is used to verify the integrity of the coating coverage of electrophoretic coatings.
Key points of selection
When selecting a model, priority should be given to detecting whether the voltage range covers the target coating thickness, and the voltage range of common instruments is between 1-35 kV. The probe design should accommodate surface curvature, with planar probes suitable for flat surfaces and roller probes better for surface inspection. The instrument should have data logging functions and external output interfaces to facilitate quality traceability. The protection level must meet the requirements of the site environment, and the intrinsically safe type should be selected for explosion-proof occasions. Calibration intervals and maintenance costs should also be included in the assessment.