Five common non-destructive testing methods and their advantages and disadvantages

Non-destructive testing refers to the use of heat, sound, light, electricity and magnetism caused by abnormal internal structure or defects of the material on the premise of inspecting the inside of mechanical materials without damaging or affecting the performance of the object being tested and without damaging the internal organization of the object being tested. and other reaction changes, using physical or chemical methods as a means, and with the help of modern technology and equipment, to analyze the structure and state of the specimen's interior and surface, as well as the type, quantity, shape, nature, location, size, distribution and changes of defects. Methods for conducting inspections and tests.

What are the common non-destructive testing methods?

 

1. Eddy current non-destructive testing

 

The principle is to use an excitation coil to generate eddy current inside the conductive material structure, and use a detection coil to measure the change in eddy current to obtain material defect information.

 

Advantages: No medium is required, the detection coil does not need to contact the detection material itself, the surface of the metal workpiece is detected quickly, the sensitivity is high, and the detection environment requirements are low.

 

Limitations: The material itself must be conductive and is only suitable for detecting metal surface defects. It requires professional analysis and judgment, customized detection solutions, and high detection costs.

 

2. Radiographic non-destructive testing

 

A non-destructive testing method that uses X-rays or gamma rays to penetrate the specimen and uses film as a device to record information. This method is the most basic and most widely used non-destructive testing method.

 

Advantages: Accurate imaging, intuitive top-down perspective, fast detection and imaging, non-destructive testing and imaging inside the workpiece, rays can penetrate thin workpieces for detection, and local differences in the image can be observed through the attenuation of penetrating rays.

 

Limitations: Due to the fact that the material itself needs to have density differences, the analysis and imaging of materials with insignificant density differences, such as some composite materials such as diamond composite sheets, are also limited by the overlap and hiding of internal images, sometimes requiring multiple times. Multi-angle shooting and professional analysis. The detection cost is high and ionizing radiation is harmful to the human body.

 

3. Ultrasonic testing for short

 

It mainly utilizes the strong penetration and good directionality of ultrasonic waves to collect the reflections of ultrasonic waves in different media. The interference waves are converted into electronic digital signals on the screen to achieve non-destructive flaw detection.

 

Advantages: It does not damage or affect the performance of the object being inspected. It can accurately image the internal structure of opaque materials. It has a wide range of detection applications and is suitable for metals, non-metals, composite materials and other materials. It locates defects more accurately. It is sensitive to area defects. It has high sensitivity, low cost, fast speed, and is harmless to human body and environment.

 

Limitations: Ultrasonic waves must rely on media and cannot propagate in vacuum. Ultrasonic waves are easily lost and scattered in the air. Generally, detection requires the use of couplant to connect the detection object. Commonly used media include (deionized water) and other media.

 

4. Penetrant inspection

 

The principle of penetrant testing is based on the capillary phenomenon of liquids and the luminescence phenomenon of solid dyes under certain conditions, and then analyzes and judges surface defects of the detected workpiece. Under capillary action, after a certain period of time, the penetrant can penetrate into the surface opening defects; remove the excess penetrant on the surface of the workpiece, and after drying, apply an adsorption medium-a developer on the surface of the workpiece to measure the morphology of the defects. and distribution status.

 

Advantages: convenient and cheap, low requirements on the testing environment, no requirements on the physical and chemical properties of the material, and sensitive to material surface defects.

 

Disadvantages: The imaging is not intuitive and the internal defects of the material cannot be determined.

 

5. Magnetic particle non-destructive testing

 

It is a method that applies a magnetic field to the inside of the test material to magnetize it, and then sprinkles magnetic powder on the surface of the workpiece to observe changes in the distribution of the magnetic powder to achieve analysis and judgment of material defects.

 

Advantages: simple and intuitive, low cost.

 

Limitations: The detection material is required to be ferromagnetic and have a smooth surface, and it can only detect the surface of the object and detect near the surface. The detection range is small, the speed is slow, and the internal defects of the material cannot be accurately judged. Some materials used in penetrant testing are toxic and harmful to the human body.