What Is a Nondestructive Evaluation?

It refers to the method of inspecting and testing the internal and surface structure, nature, and state of the test piece by means of physical or chemical methods and advanced technology and equipment without damaging the test piece.

Chinese name: Nondestructive inspection
Foreign name: Nondestructive inspection

Purpose: Guarantee product quality
Stage: NDT, NDT and NDT

Definition of non-destructive testing

Purpose of NDT

The application of non-destructive testing techniques can achieve the following purposes: [span]

1.Ensure product quality

2.Ensure safe use

3.Improve manufacturing processes and reduce production costs

Development of non-destructive testing

The development of non-destructive testing technology has gone through three stages.

That is: non-destructive testing, non-destructive testing, and non-destructive evaluation, where non-destructive testing is the name of the early stage and its meaning is to detect and find defects; non-destructive testing is the name of the current stage. Some other information, such as structure, nature, status, etc .; Nondestructive evaluation is a new stage that is about to enter or is entering. It not only requires finding defects, exploring the structure, nature, status of the test piece, but also obtaining more comprehensive and accurate information. , Comprehensive information, such as information about the shape, size, position, orientation, inclusions, defect organization, residual stress, etc. of the defect, it must be combined with imaging technology, automation technology, computer data analysis and processing technology, And knowledge in material mechanics and other fields, giving a comprehensive and accurate evaluation of the quality and performance of the test piece or product

Classification of non-destructive testing

Non-destructive inspection usually includes five general methods: ultrasonic inspection, radiographic inspection, magnetic particle inspection, penetration inspection, and eddy current inspection .

Ultrasonic inspection: When ultrasonic waves propagate in the material under inspection, the method of detecting the defects according to the effect of the acoustic properties of the material defects on the propagation of ultrasonic waves. Ultrasonic inspection of internal and surface defects is common.

X-ray inspection : A non-destructive inspection method for internal defects of metals using X-rays and other rays.

Magnetic particle inspection: A non-destructive inspection method for discontinuities on the surface and near surface of a test piece using magnetic leakage and a suitable inspection medium.

Penetrant inspection: By applying a penetrant, removing excess parts with a detergent, and then applying a developer to obtain a defect display on the surface that is open on the part.

Eddy current inspection: A non-destructive testing method that analyzes the quality status of a test piece by using the eddy current in the test piece.

Ultrasonic inspection and radiographic inspection are the most widely used inspection methods. As long as it is used for internal defect inspection, for surface inspection, magnetic particle inspection is mainly used. As long as it is ferromagnetic material, magnetic particle inspection is preferred.

In the industry, the ultrasonic inspection is mainly metal, and it can also be used for other inspection objects; the radiographic inspection object is also very wide, mainly metal; the magnetic particle inspection can only be applied to ferromagnetic materials; the penetration inspection can be used for both metal and For non-metallic materials; eddy current testing can only be applied to conductive materials.

Introduction to the principles of various nondestructive testing methods

Without damaging the material under test, inspection techniques that check the material's internal or surface defects, or determine certain physical quantities, properties, and tissue states of the material. Widely used in the detection of metal materials, non-metal materials, composite materials and their products, and some electronic components. Commonly used non-destructive testing techniques are:

Non-destructive inspection Ray inspection.

X-ray or -ray is used to detect the defect of the test object through the difference in intensity attenuation when penetrating each part of the test object.

If the rays that have been absorbed to different degrees are projected onto the X-ray film, after development, a photo showing the change in the thickness of the object and the internal defects can be obtained. If you use a fluorescent screen instead of film, you can directly observe the internal condition of the object under inspection.

Non-destructive testing Ultrasonic testing.

Use the influence of the acoustic characteristics of the object or defects on the propagation of ultrasonic waves to detect the defects or certain physical characteristics of the object. The ultrasonic frequency commonly used in ultrasonic testing is 0.5 to 5 megahertz (MHz). The most commonly used ultrasonic testing is pulse reflection testing.

Non-destructive inspection Magnetic particle inspection.

Defects on or near the surface are detected by the accumulation of magnetic particles in the leakage magnetic field near the object defect. The object to be detected must be ferromagnetic.

Non-destructive testing Penetrant flaw detection.

Surface imperfections are detected by the permeability of certain liquids to narrow gaps. Commonly used penetrants are liquids containing colored dyes or fluorescence.

Non-destructive testing Eddy current testing

Since the magnitude of the eddy current varies depending on whether there are defects in the workpiece, the magnitude of the coil current change can reflect the presence or absence of defects.

In addition, new non-destructive testing technologies such as neutron radiography, laser holography, ultrasonic holography, infrared detection, and microwave detection have also been developed and applied.