Definition
A high-voltage EDM leak detector is a non-destructive testing equipment used to detect defects such as pinholes and cracks in non-conductive coatings or linings. It locates discontinuities by applying a high-voltage electricity that creates a visible or audible EDM phenomenon at the coating defect. This instrument is widely used in industrial anti-corrosion, pipeline engineering, storage tank manufacturing, and other fields, and is a key tool to ensure the integrity and anti-corrosion effect of coatings.
Principle
The instrument works on the principle of high-voltage discharge. When the electrode approaches or touches the surface of the coating being measured, the high-voltage electricity generated by the instrument creates an electric field between the electrode and the substrate. If the coating is intact and defective, its insulating properties will prevent current from passing through; If the coating is defective, the electric field strength is concentrated at the defect, breaking through the air to produce an electric spark, and the instrument usually emits an audible and visual alarm. The discharge voltage can be adjusted according to the thickness of the coating, and the basic relationship followed can be expressed as: V = k × d, where V is the detection voltage, d is the coating thickness, and k is the coefficient related to the material.
Measurement method
Before measurement, the detection voltage should be set according to the coating material, thickness and standard requirements. During operation, the ground wire needs to be reliably connected to the substrate, and the electrode scans the coating surface at a constant speed, maintaining an appropriate distance from the surface. When an EDM is found, mark the location of the defect. Common methods include contact scanning and non-contact scanning, depending on coating sensitivity and conditions. After testing, the number and distribution of defects should be recorded, and the coating quality should be evaluated according to relevant standards.
Influencing factors
Coating thickness and uniformity directly affect the selection of detection voltage, and being too thin or too thick can cause misjudgment. Ambient humidity and temperature may change the dielectric strength of the air and affect the discharge sensitivity. Substrate conductivity and grounding are key factors, and poor grounding can lead to detection failure. The stability of the operator's movement speed and electrode distance can also affect defect detection rates. In addition, the coating material characteristics and surface cleanliness should not be overlooked.
Applications
The instrument is suitable for a variety of industrial scenarios. In the petrochemical field, it is used to detect the anti-corrosion coating of storage tanks and pipelines; In shipbuilding, check the integrity of the hull coating; In construction projects, evaluate the anti-corrosion layer of underground pipelines; It can also be used for coating quality control in industries such as automobile manufacturing and container production. When applying, refer to various industry standards, such as ISO 2746, ASTM D5162, etc., to ensure the standardization of testing.
Selection considerations
The testing needs should be comprehensively considered when selecting. The voltage output range should cover the voltage corresponding to the thickness of the coating to be measured and have a continuously adjustable function. The instrument should have a stable short-circuit protection and overload protection mechanism to ensure operational safety. Choose portable or stationary equipment based on site conditions and pay attention to its environmental adaptability. In addition, the alarm style, endurance and compliance standard system are also important reference factors. It is recommended to test and verify based on actual application scenarios.