What Is Nondestructive Testing?

Non-destructive testing refers to the use of changes in the reaction of heat, sound, light, electricity, and magnetism caused by the abnormal structure of the material or the existence of the defect without damaging or affecting the performance of the test object and harming the internal organization of the test object. , Using physical or chemical methods as a means, with the help of modern technology and equipment, to inspect the internal and surface structure, properties, status, and type, nature, quantity, shape, location, size, distribution, and changes of the test piece And test methods ^[1] . Non-destructive testing is an indispensable and effective tool for industrial development. It reflects the level of industrial development in a country to a certain extent. The importance of non-destructive testing has been recognized, mainly including radiographic inspection (RT), ultrasonic testing (UT), and magnetic particle testing. (MT) and liquid penetration test (PT). Other non-destructive testing methods include eddy current testing (ECT), acoustic emission testing (AE), thermal imaging / infrared (TIR), leakage test (LT), alternating field measurement technology (ACFMT), magnetic flux leakage inspection (MFL), and far-field testing Detection method (RFT), ultrasonic diffraction time difference method (TOFD), etc.

Nondestructive testing

(Detection Technology)

Non-destructive testing is Non Destructive Testing.

Non-destructive testing uses the characteristics of sound, light, magnetism, and electricity of a substance to detect whether there is a defect or non-uniformity in the test object without damaging or affecting the performance of the test object, and gives the size and location of the defect. , Nature and quantity. 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 test object when it is tested; the second is comprehensive, because the test is non-destructive, so 100% of the test can be performed when necessary This is not possible with destructive testing; the third is full-scale. Destructive testing is generally only applicable to the detection of raw materials, such as tensile, compression, and bending commonly used in mechanical engineering. Destructive testing is aimed at For manufacturing raw materials, destructive testing cannot be performed on finished products and in-use supplies unless they are not intended to continue service, and non-destructive testing does not damage the performance of the tested object. Therefore, it can not only inspect the raw materials for manufacturing, all intermediate processes, and the final product, but also the equipment in service.

Non-destructive inspection visual inspection range: 1. Inspection of weld surface defects. Check the welding quality such as cracks, incomplete penetration and leaks on the surface of the weld. 2. Status check. Inspect defects such as surface cracks, peeling, pulling lines, scratches, pits, bumps, spots, corrosion, etc. 3. Inner cavity inspection. After certain products (such as worm pumps, engines, etc.) work, endoscopic inspections are performed according to the items specified in the technical requirements. 4. Assembly inspection. When required and required, use the same 3D industrial video endoscope to check the assembly quality; after assembly or a certain 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 check. Check for residual debris, foreign matter, etc. in the product cavity.

Non-destructive testing is no longer just using X-rays, and various physical phenomena including sound, electricity, magnetism, electromagnetic waves, neutrons, lasers, etc. are almost all used for non-destructive testing, such as: ultrasonic testing, eddy current testing, magnetic particle testing, Ray detection, penetration detection, visual detection, infrared detection, microwave detection, leak detection, acoustic emission detection, magnetic leakage detection, magnetic memory detection, thermal neutron photography detection, laser speckle imaging detection, fiber grating sensing technology, etc. Etc., and new methods and technologies are constantly being developed and applied.
Some seemingly traditional NDT methods have actually developed many new technologies, such as:
Radiographic inspection-traditional techniques are: film radiography (X-rays and gamma rays). New technologies include accelerator high-energy X-ray photography, digital radiography (DR), computer radiography (CR, similar to digital photography), computer tomography (CT), ray diffraction, and so on.

1.Non-destructive

There are many non-destructive testing methods. According to the investigation and analysis of NASA, they believe that there are about 70 types that can be divided into six categories. However, the following are more common in practical applications:

Visual inspection (VT)

Visual inspection is relatively rare in China, but it is the primary method of the first stage of non-destructive testing that is very important internationally. According to international practice, visual inspection should be performed first to confirm that it will not affect subsequent inspections, and then four major routine inspections will be performed. For example, BINDT's PCN certification has special VT 1, 2 and 3 assessments, as well as special certification requirements. VT is often used for visual inspection of welds. Welds themselves have process qualification standards. They can be initially inspected by visual inspection and direct measurement of dimensions. If unqualified appearance defects such as undercuts are found, they must be polished or trimmed first. Only do other in-depth instrument testing. For example, the surface of the weldment and the surface of the casting have more VTs, but there are fewer forgings, and the inspection standards are basically consistent.

Radiography (RT)

Means

1. Product drawings

Drawings are the most basic technical information used in production and the basis for processing and inspection. Especially in the technical requirements of drawings, the quality grades of raw materials, parts, products, specific requirements, and whether non-destructive inspection is required are often specified.

2. Related standards

Production companies often have to implement relevant standards, such as: enterprise standards, industry standards, national standards, international standards, and so on. These are all guidance documents for product processing, and naturally they are also guidance documents for implementing non-destructive testing. In specific standards, inspection objects, inspection methods, inspection scales, etc. are often specified in detail.

3. Technical documents

Various technical documents issued by the product production technology department, such as process regulations, inspection cards, product inspection reports, repair orders, and so on. Sometimes additional inspection requirements are added or changed.

4. Order contract

The special inspection requirements and quality control clauses of some products may sometimes be emphasized in more detail in the order contract, which should attract special attention.

The term "calibration" has been used in classic meter management and is now called "calibration" in metrology management.

Calibration (Calibration) is all the work to determine the indication error of the measuring instrument (including the determination of other measuring performance if necessary).

First, the similarities and differences between calibration and verification

Calibration and verification are two different concepts, but there is a close relationship between the two. Calibration generally uses a measuring instrument (called a standard instrument) with a higher accuracy than the calibrated measuring instrument to compare with the calibrated measuring instrument to determine the indication error of the calibrated measuring instrument, sometimes including some metrological performance, but often it is calibrated The measuring instrument only needs to determine the indication error. If calibration is the verification content of the indication error in the verification work, then the calibration can be said to be a part of the verification work, but the calibration cannot be regarded as a verification, and the requirements of the calibration are not as good as the verification. So strict, the calibration can be performed at the production site, and the verification must be performed in the verification room.

Some people understand the calibration as the process of adjusting the measuring instrument to a specified error range. In fact, this is not accurate enough. Although it can be adjusted during calibration, it is not equal to calibration.

Basic requirements for calibration

The basic requirements for calibration should be as follows:

(1) If the environmental conditions are calibrated in a calibration (calibration) room, the environmental conditions shall meet the requirements of the laboratory such as temperature and humidity. If the calibration is performed on site, the environmental conditions shall prevail to the conditions that can meet the on-site use of the instrument.

(2) The error limit of the instrument as a standard instrument for calibration should be 1/3 ~ 1/10 of the error limit of the calibrated meter.

(3) Although the calibration of personnel is different from the verification, the personnel performing the calibration shall also be validated and obtain the corresponding certificate of conformity. Only the certificate holder can issue a calibration certificate and calibration report, and only such certificates and reports are available. Think it works.