Nondestructive Testing Principle And Characteristics Overview

non-destructive Testing is non-destructive Testing, abbreviated as NDT (or NDE, non-destructive examination), also known as non-destructive testing, on the premise of not damaging or affecting the performance of the tested object. The technology of detecting defects, chemical and physical parameters of materials, parts and equipment by using X-ray, ultrasonic, infrared, electromagnetic and other principles and technologies combined with instruments. Common such as ultrasonic detection of cracks in welds.

Common non-destructive testing methods:

Visual inspection (VT) : is the visual observation of internal or external areas, installations or components to look for obvious signs of damage, failure or abnormality.

Ultrasonic testing (abbreviated UT) : refers to the use of ultrasonic and workpiece interaction, reflection, transmission and scattering echo analysis, so as to detect and characterize the macro defects, geometric characteristics, organizational structure and mechanical properties of the workpiece, and then evaluate its specific application technology.

X-ray detection (abbreviated RT) : It is the use of X-ray or gamma rays to penetrate the workpiece, through the workpiece's rays to expose the industrial film, the film is chemically processed into a negative, the negative is placed on the special viewing lamp observation, you can see the different shapes of the image composed of different blackness.

Magnetic particle detection (MT) : The method of observing defects using magnetic particle as a display medium. According to the type of magnetic powder medium applied during magnetization, the detection methods are divided into wet method and dry method. According to the time of applying magnetic powder on the workpiece, the test methods are divided into continuous method and residual magnetic method.

Penetration testing (abbreviated PT) is a non-destructive testing technique based on the principle of capillary interaction, mainly used to detect surface opening defects of non-porous metal or non-metallic parts

Eddy current testing (abbreviated ET) : It is a nondestructive testing that uses the principle of electromagnetic induction to nondestructively assess certain properties of conductive materials and their workpieces by measuring the changes of eddy current induced in the workpieces under test, or to find defects.

Working principle of non-destructive testing:

Non-destructive testing is the use of material acoustic, optical, magnetic and electrical characteristics, without damaging or affecting the performance of the tested object under the premise of detecting whether there are defects or inhomogeneity in the tested object, giving the size, location, nature and quantity of defects and other information. Compared with destructive testing, non-destructive testing has the following characteristics. The first is non-destructive, because it will not damage the performance of the tested object during detection; Second, it has comprehensiveness, because the detection is non-destructive, it can conduct 100% comprehensive detection of the tested object when necessary, which is impossible for destructive detection; Destructive testing is generally only applicable to the testing of raw materials, such as tensile, compression, bending, etc., commonly used in mechanical engineering. Destructive testing is carried out for raw materials used in manufacturing. For finished products and supplies, unless they are not prepared to continue to serve, destructive testing cannot be carried out. Non-destructive testing does not damage the performance of the tested object. Therefore, it can not only test the raw materials used in manufacturing, the intermediate process links, until the final product, but also test the equipment in service.

Non-destructive inspection Visual inspection range:

1. Inspection of weld surface defects. Check weld surface cracks, underpenetration and leakage.

2. Status check. Check surface cracks, peeling, threading, scratches, pits, bumps, spots, corrosion and other defects.

3. Internal cavity examination. When some products (such as worm gear pumps, engines, etc.) work, endoscopic testing is carried out according to the technical requirements.

4. Assembly inspection. When required, the same 3D industrial video endoscope is used to check the assembly quality; After assembly or a process is completed, check whether the assembly position of each component meets the requirements of the drawing or technical conditions; Whether there are assembly defects.

5, excess inspection. Check product internal cavity residual internal chips, foreign objects and other excess.

Features and advantages of non-destructive testing:

1, non-destructive non-destructive - means that at the same time of obtaining test results, in addition to removing unqualified products, no loss of parts. Therefore, the scale of inspection is not limited by the number of parts, and it can be sampled for inspection, and general inspection can be used if necessary. Therefore, more flexibility (general inspection, random inspection can be) and reliability.

2, mutual tolerance mutual tolerance - refers to the mutual tolerance of inspection methods, that is, the same part can be used at the same time or in turn different inspection methods; And the same test can be repeated. This is also the benefit of being non-destructive.

3, dynamic dynamic - this means that the non-destructive testing method can be used to test the parts in use, and can timely investigate the cumulative impact of the product running period. Therefore, the failure mechanism of the structure can be ascertained.

4, rigor rigor -- refers to the rigor of non-destructive testing technology. First of all, non-destructive testing requires special instruments and equipment; At the same time, specially trained inspectors are required to operate according to strict procedures and standards.

5. Divergence of test results Divergence of test results - different testers may have differences on the test results of the same specimen. Especially in the ultrasonic inspection, the same inspection project should be completed by two inspectors. A "consultation" is required. In summary, the characteristics of non-destructive testing are: non-destructive, mutual tolerance, dynamic, strict and the divergence of test results.