Visual inspection scope, working principle and characteristics of nondestructive test

Date：2022-03-03 14:55:00Views：1205

Nondestructive testing is a modern way of testing and evaluation without damaging the items to be tested. Nondestructive testing is no longer just using X-ray nondestructive testing, including acoustic, electrical, magnetic, electromagnetic wave, neutron, laser and other physical phenomena are almost used in nondestructive testing, such as ultrasonic nondestructive testing, eddy current nondestructive testing, magnetic particle nondestructive testing, radiographic nondestructive testing, penetrant testing, visual testing, infrared testing, microwave testing, leakage testing Acoustic emission detection, magnetic flux leakage detection, magnetic memory detection, thermal neutron photography detection, laser speckle imaging detection, fiber Bragg grating sensing technology detection and so on, and new methods and technologies are constantly developed and applied.

Principle of nondestructive testing

Nondestructive testing is to use the acoustic, optical, magnetic and electrical characteristics of materials to detect whether there are defects or non-uniformity in the tested object without damaging or affecting the service performance of the tested object, and give information such as the size, location, nature and quantity of defects. Compared with destructive testing, nondestructive testing has the following characteristics.

The first is non-destructive, because it will not damage the service performance of the tested object when testing;Second, it is comprehensive, because the detection is non-destructive, 100% comprehensive detection can be carried out on the tested object when necessary, which is impossible for destructive detection;Third, it has the whole process, destructive testing is generally only applicable to the testing of raw materials, such as tension, compression, bending, etc. commonly used in mechanical engineering. Destructive testing is carried out for manufacturing raw materials.

For finished products and articles in process, unless they are not prepared to continue service, destructive testing cannot be carried out, while nondestructive testing does not damage the service performance of the tested object. Therefore, it can not only test the whole process of raw materials for manufacturing, intermediate process links and final products, but also test the equipment in service.

NDT features

1. Non destructive

Non destructive - it means that while the test results are obtained, the parts are not lost except for the unqualified products. Therefore, the inspection scale is not limited by the number of parts. It can not only be sampled for inspection, but also be subject to general inspection when necessary. Therefore, it has more flexibility (general inspection and sampling inspection) and reliability.

2. Mutual compatibility

Compatibility - refers to the compatibility of inspection methods, that is, the same part can adopt different inspection methods at the same time or in turn; And the same test can be repeated. This is also the benefit of non-destructive.

3. Dynamic

Dynamic - this means that NDT methods can inspect parts in use and timely investigate the cumulative impact of product operation period. Therefore, the failure mechanism of the structure can be found out.

4. Strictness

Strictness - refers to the strictness of NDT technology. First, NDT requires special instruments and equipment; At the same time, specially trained inspectors are also required to operate in accordance with strict procedures and standards.

5. Divergence of test results

Divergence of inspection results - different inspectors may have different inspection results for the same specimen. Especially in ultrasonic inspection, the same inspection item should be completed by two inspectors. "Consultation" is required.

To sum up, the characteristics of nondestructive testing are: non-destructive, mutual compatibility, dynamics, strictness and the divergence of testing results.

NDT visual inspection scope:

1. Weld surface defect inspection

Check the welding quality such as weld surface crack, incomplete penetration and weld leakage.

2. Status check

Non destructive testing shall be conducted to check the surface cracks, peeling, pull wires, scratches, pits, bulges, spots, corrosion and other defects.

3. Lumen examination

When some products (such as worm gear pump, engine, etc.) work, endoscopic NDT shall be carried out according to the items specified in the technical requirements.

4. Assembly inspection

When required and needed, use the same three-dimensional industrial video endoscope to check the assembly quality; After assembly or a process is completed, check whether the assembly position of all parts and components meets the requirements of drawings or technical conditions; Whether there are assembly defects.

5. Surplus inspection

Check the residual internal debris, foreign objects and other residues in the inner cavity of the product.

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